(feat): Initial Version of Custom Commands (#4572)

17 files changed, 1008 insertions, 96 deletions

diff --git a/docs/cli/commands.md b/docs/cli/commands.md
index 97527a68..7f11094a 100644
--- a/docs/cli/commands.md
+++ b/docs/cli/commands.md
@@ -6,6 +6,8 @@ Gemini CLI supports several built-in commands to help you manage your session, c
 
 Slash commands provide meta-level control over the CLI itself.
 
+### Built-in Commands
+
 - **`/bug`**
   - **Description:** File an issue about Gemini CLI. By default, the issue is filed within the GitHub repository for Gemini CLI. The string you enter after `/bug` will become the headline for the bug being filed. The default `/bug` behavior can be modified using the `bugCommand` setting in your `.gemini/settings.json` files.
 
@@ -38,7 +40,7 @@ Slash commands provide meta-level control over the CLI itself.
   - **Description:** Lists all active extensions in the current Gemini CLI session. See [Gemini CLI Extensions](../extension.md).
 
 - **`/help`** (or **`/?`**)
-  - **Description:** Display help information about the Gemini CLI, including available commands and their usage.
+  - **Description:** Display help information about Gemini CLI, including available commands and their usage.
 
 - **`/mcp`**
   - **Description:** List configured Model Context Protocol (MCP) servers, their connection status, server details, and available tools.
@@ -93,6 +95,91 @@ Slash commands provide meta-level control over the CLI itself.
 - **`/quit`** (or **`/exit`**)
   - **Description:** Exit Gemini CLI.
 
+### Custom Commands
+
+For a quick start, see the [example](#example-a-pure-function-refactoring-command) below.
+
+Custom commands allow you to save and reuse your favorite or most frequently used prompts as personal shortcuts within Gemini CLI. You can create commands that are specific to a single project or commands that are available globally across all your projects, streamlining your workflow and ensuring consistency.
+
+#### File Locations & Precedence
+
+Gemini CLI discovers commands from two locations, loaded in a specific order:
+
+1.  **User Commands (Global):** Located in `~/.gemini/commands/`. These commands are available in any project you are working on.
+2.  **Project Commands (Local):** Located in `<your-project-root>/.gemini/commands/`. These commands are specific to the current project and can be checked into version control to be shared with your team.
+
+If a command in the project directory has the same name as a command in the user directory, the **project command will always be used.** This allows projects to override global commands with project-specific versions.
+
+#### Naming and Namespacing
+
+The name of a command is determined by its file path relative to its `commands` directory. Subdirectories are used to create namespaced commands, with the path separator (`/` or `\`) being converted to a colon (`:`).
+
+- A file at `~/.gemini/commands/test.toml` becomes the command `/test`.
+- A file at `<project>/.gemini/commands/git/commit.toml` becomes the namespaced command `/git:commit`.
+
+#### TOML File Format (v1)
+
+Your command definition files must be written in the TOML format and use the `.toml` file extension.
+
+##### Required Fields
+
+- `prompt` (String): The prompt that will be sent to the Gemini model when the command is executed. This can be a single-line or multi-line string.
+
+##### Optional Fields
+
+- `description` (String): A brief, one-line description of what the command does. This text will be displayed next to your command in the `/help` menu. **If you omit this field, a generic description will be generated from the filename.**
+
+---
+
+#### Example: A "Pure Function" Refactoring Command
+
+Let's create a global command that asks the model to refactor a piece of code.
+
+**1. Create the file and directories:**
+
+First, ensure the user commands directory exists, then create a `refactor` subdirectory for organization and the final TOML file.
+
+```bash
+mkdir -p ~/.gemini/commands/refactor
+touch ~/.gemini/commands/refactor/pure.toml
+```
+
+**2. Add the content to the file:**
+
+Open `~/.gemini/commands/refactor/pure.toml` in your editor and add the following content. We are including the optional `description` for best practice.
+
+```toml
+# In: ~/.gemini/commands/refactor/pure.toml
+# This command will be invoked via: /refactor:pure
+
+description = "Asks the model to refactor the current context into a pure function."
+
+prompt = """
+Please analyze the code I've provided in the current context.
+Refactor it into a pure function.
+
+Your response should include:
+1. The refactored, pure function code block.
+2. A brief explanation of the key changes you made and why they contribute to purity.
+"""
+```
+
+**3. Run the Command:**
+
+That's it! You can now run your command in the CLI. First, you might add a file to the context, and then invoke your command:
+
+```
+> @my-messy-function.js
+> /refactor:pure
+```
+
+Gemini CLI will then execute the multi-line prompt defined in your TOML file.
+
+This initial version of custom commands is focused on static prompts. Future updates are planned to introduce more dynamic capabilities, including:
+
+- **Argument Support:** Passing arguments from the command line directly into your `prompt` template.
+- **Shell Execution:** Creating commands that can run local shell scripts to gather context before running the prompt.
+
 ## At commands (`@`)
 
 At commands are used to include the content of files or directories as part of your prompt to Gemini. These commands include git-aware filtering.
diff --git a/package-lock.json b/package-lock.json
index e35d9bc6..1b34f994 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -17,6 +17,7 @@
         "@types/micromatch": "^4.0.9",
         "@types/mime-types": "^3.0.1",
         "@types/minimatch": "^5.1.2",
+        "@types/mock-fs": "^4.13.4",
         "@types/shell-quote": "^1.7.5",
         "@vitest/coverage-v8": "^3.1.1",
         "concurrently": "^9.2.0",
@@ -33,6 +34,7 @@
         "json": "^11.0.0",
         "lodash": "^4.17.21",
         "memfs": "^4.17.2",
+        "mock-fs": "^5.5.0",
         "prettier": "^3.5.3",
         "react-devtools-core": "^4.28.5",
         "typescript-eslint": "^8.30.1",
@@ -1034,6 +1036,12 @@
         "url": "https://github.com/sponsors/nzakas"
       }
     },
+    "node_modules/@iarna/toml": {
+      "version": "2.2.5",
+      "resolved": "https://registry.npmjs.org/@iarna/toml/-/toml-2.2.5.tgz",
+      "integrity": "sha512-trnsAYxU3xnS1gPHPyU961coFyLkh4gAD/0zQ5mymY4yOZ+CYvsPqUbOFSw0aDM4y0tV7tiFxL/1XfXPNC6IPg==",
+      "license": "ISC"
+    },
     "node_modules/@isaacs/cliui": {
       "version": "8.0.2",
       "resolved": "https://registry.npmjs.org/@isaacs/cliui/-/cliui-8.0.2.tgz",
@@ -2368,6 +2376,16 @@
       "integrity": "sha512-K0VQKziLUWkVKiRVrx4a40iPaxTUefQmjtkQofBkYRcoaaL/8rhwDWww9qWbrgicNOgnpIsMxyNIUM4+n6dUIA==",
       "license": "MIT"
     },
+    "node_modules/@types/mock-fs": {
+      "version": "4.13.4",
+      "resolved": "https://registry.npmjs.org/@types/mock-fs/-/mock-fs-4.13.4.tgz",
+      "integrity": "sha512-mXmM0o6lULPI8z3XNnQCpL0BGxPwx1Ul1wXYEPBGl4efShyxW2Rln0JOPEWGyZaYZMM6OVXM/15zUuFMY52ljg==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@types/node": "*"
+      }
+    },
     "node_modules/@types/node": {
       "version": "20.19.1",
       "resolved": "https://registry.npmjs.org/@types/node/-/node-20.19.1.tgz",
@@ -7820,6 +7838,16 @@
         "node": ">=16 || 14 >=14.17"
       }
     },
+    "node_modules/mock-fs": {
+      "version": "5.5.0",
+      "resolved": "https://registry.npmjs.org/mock-fs/-/mock-fs-5.5.0.tgz",
+      "integrity": "sha512-d/P1M/RacgM3dB0sJ8rjeRNXxtapkPCUnMGmIN0ixJ16F/E4GUZCvWcSGfWGz8eaXYvn1s9baUwNjI4LOPEjiA==",
+      "dev": true,
+      "license": "MIT",
+      "engines": {
+        "node": ">=12.0.0"
+      }
+    },
     "node_modules/module-details-from-path": {
       "version": "1.0.4",
       "resolved": "https://registry.npmjs.org/module-details-from-path/-/module-details-from-path-1.0.4.tgz",
@@ -11622,6 +11650,7 @@
       "version": "0.1.13",
       "dependencies": {
         "@google/gemini-cli-core": "file:../core",
+        "@iarna/toml": "^2.2.5",
         "@types/update-notifier": "^6.0.8",
         "command-exists": "^1.2.9",
         "diff": "^7.0.0",
diff --git a/package.json b/package.json
index a64b7578..e1213dce 100644
--- a/package.json
+++ b/package.json
@@ -60,6 +60,7 @@
     "@types/micromatch": "^4.0.9",
     "@types/mime-types": "^3.0.1",
     "@types/minimatch": "^5.1.2",
+    "@types/mock-fs": "^4.13.4",
     "@types/shell-quote": "^1.7.5",
     "@vitest/coverage-v8": "^3.1.1",
     "concurrently": "^9.2.0",
@@ -76,6 +77,7 @@
     "json": "^11.0.0",
     "lodash": "^4.17.21",
     "memfs": "^4.17.2",
+    "mock-fs": "^5.5.0",
     "prettier": "^3.5.3",
     "react-devtools-core": "^4.28.5",
     "typescript-eslint": "^8.30.1",
diff --git a/packages/cli/package.json b/packages/cli/package.json
index 31b5f199..faebfea3 100644
--- a/packages/cli/package.json
+++ b/packages/cli/package.json
@@ -29,6 +29,7 @@
   },
   "dependencies": {
     "@google/gemini-cli-core": "file:../core",
+    "@iarna/toml": "^2.2.5",
     "@types/update-notifier": "^6.0.8",
     "command-exists": "^1.2.9",
     "diff": "^7.0.0",
diff --git a/packages/cli/src/services/BuiltinCommandLoader.test.ts b/packages/cli/src/services/BuiltinCommandLoader.test.ts
index 642309dc..0e64b1ac 100644
--- a/packages/cli/src/services/BuiltinCommandLoader.test.ts
+++ b/packages/cli/src/services/BuiltinCommandLoader.test.ts
@@ -72,7 +72,7 @@ describe('BuiltinCommandLoader', () => {
 
   it('should correctly pass the config object to command factory functions', async () => {
     const loader = new BuiltinCommandLoader(mockConfig);
-    await loader.loadCommands();
+    await loader.loadCommands(new AbortController().signal);
 
     expect(ideCommandMock).toHaveBeenCalledTimes(1);
     expect(ideCommandMock).toHaveBeenCalledWith(mockConfig);
@@ -84,7 +84,7 @@ describe('BuiltinCommandLoader', () => {
     // Override the mock's behavior for this specific test.
     ideCommandMock.mockReturnValue(null);
     const loader = new BuiltinCommandLoader(mockConfig);
-    const commands = await loader.loadCommands();
+    const commands = await loader.loadCommands(new AbortController().signal);
 
     // The 'ide' command should be filtered out.
     const ideCmd = commands.find((c) => c.name === 'ide');
@@ -97,7 +97,7 @@ describe('BuiltinCommandLoader', () => {
 
   it('should handle a null config gracefully when calling factories', async () => {
     const loader = new BuiltinCommandLoader(null);
-    await loader.loadCommands();
+    await loader.loadCommands(new AbortController().signal);
     expect(ideCommandMock).toHaveBeenCalledTimes(1);
     expect(ideCommandMock).toHaveBeenCalledWith(null);
     expect(restoreCommandMock).toHaveBeenCalledTimes(1);
@@ -106,7 +106,7 @@ describe('BuiltinCommandLoader', () => {
 
   it('should return a list of all loaded commands', async () => {
     const loader = new BuiltinCommandLoader(mockConfig);
-    const commands = await loader.loadCommands();
+    const commands = await loader.loadCommands(new AbortController().signal);
 
     const aboutCmd = commands.find((c) => c.name === 'about');
     expect(aboutCmd).toBeDefined();
diff --git a/packages/cli/src/services/FileCommandLoader.test.ts b/packages/cli/src/services/FileCommandLoader.test.ts
new file mode 100644
index 00000000..518c9230
--- /dev/null
+++ b/packages/cli/src/services/FileCommandLoader.test.ts
@@ -0,0 +1,235 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { FileCommandLoader } from './FileCommandLoader.js';
+import {
+  Config,
+  getProjectCommandsDir,
+  getUserCommandsDir,
+} from '@google/gemini-cli-core';
+import mock from 'mock-fs';
+import { assert } from 'vitest';
+import { createMockCommandContext } from '../test-utils/mockCommandContext.js';
+
+const mockContext = createMockCommandContext();
+
+describe('FileCommandLoader', () => {
+  const signal: AbortSignal = new AbortController().signal;
+
+  afterEach(() => {
+    mock.restore();
+  });
+
+  it('loads a single command from a file', async () => {
+    const userCommandsDir = getUserCommandsDir();
+    mock({
+      [userCommandsDir]: {
+        'test.toml': 'prompt = "This is a test prompt"',
+      },
+    });
+
+    const loader = new FileCommandLoader(null as unknown as Config);
+    const commands = await loader.loadCommands(signal);
+
+    expect(commands).toHaveLength(1);
+    const command = commands[0];
+    expect(command).toBeDefined();
+    expect(command.name).toBe('test');
+
+    const result = await command.action?.(mockContext, '');
+    if (result?.type === 'submit_prompt') {
+      expect(result.content).toBe('This is a test prompt');
+    } else {
+      assert.fail('Incorrect action type');
+    }
+  });
+
+  it('loads multiple commands', async () => {
+    const userCommandsDir = getUserCommandsDir();
+    mock({
+      [userCommandsDir]: {
+        'test1.toml': 'prompt = "Prompt 1"',
+        'test2.toml': 'prompt = "Prompt 2"',
+      },
+    });
+
+    const loader = new FileCommandLoader(null as unknown as Config);
+    const commands = await loader.loadCommands(signal);
+
+    expect(commands).toHaveLength(2);
+  });
+
+  it('creates deeply nested namespaces correctly', async () => {
+    const userCommandsDir = getUserCommandsDir();
+
+    mock({
+      [userCommandsDir]: {
+        gcp: {
+          pipelines: {
+            'run.toml': 'prompt = "run pipeline"',
+          },
+        },
+      },
+    });
+    const loader = new FileCommandLoader({
+      getProjectRoot: () => '/path/to/project',
+    } as Config);
+    const commands = await loader.loadCommands(signal);
+    expect(commands).toHaveLength(1);
+    expect(commands[0]!.name).toBe('gcp:pipelines:run');
+  });
+
+  it('creates namespaces from nested directories', async () => {
+    const userCommandsDir = getUserCommandsDir();
+    mock({
+      [userCommandsDir]: {
+        git: {
+          'commit.toml': 'prompt = "git commit prompt"',
+        },
+      },
+    });
+
+    const loader = new FileCommandLoader(null as unknown as Config);
+    const commands = await loader.loadCommands(signal);
+
+    expect(commands).toHaveLength(1);
+    const command = commands[0];
+    expect(command).toBeDefined();
+    expect(command.name).toBe('git:commit');
+  });
+
+  it('overrides user commands with project commands', async () => {
+    const userCommandsDir = getUserCommandsDir();
+    const projectCommandsDir = getProjectCommandsDir(process.cwd());
+    mock({
+      [userCommandsDir]: {
+        'test.toml': 'prompt = "User prompt"',
+      },
+      [projectCommandsDir]: {
+        'test.toml': 'prompt = "Project prompt"',
+      },
+    });
+
+    const loader = new FileCommandLoader({
+      getProjectRoot: () => process.cwd(),
+    } as Config);
+    const commands = await loader.loadCommands(signal);
+
+    expect(commands).toHaveLength(1);
+    const command = commands[0];
+    expect(command).toBeDefined();
+
+    const result = await command.action?.(mockContext, '');
+    if (result?.type === 'submit_prompt') {
+      expect(result.content).toBe('Project prompt');
+    } else {
+      assert.fail('Incorrect action type');
+    }
+  });
+
+  it('ignores files with TOML syntax errors', async () => {
+    const userCommandsDir = getUserCommandsDir();
+    mock({
+      [userCommandsDir]: {
+        'invalid.toml': 'this is not valid toml',
+        'good.toml': 'prompt = "This one is fine"',
+      },
+    });
+
+    const loader = new FileCommandLoader(null as unknown as Config);
+    const commands = await loader.loadCommands(signal);
+
+    expect(commands).toHaveLength(1);
+    expect(commands[0].name).toBe('good');
+  });
+
+  it('ignores files that are semantically invalid (missing prompt)', async () => {
+    const userCommandsDir = getUserCommandsDir();
+    mock({
+      [userCommandsDir]: {
+        'no_prompt.toml': 'description = "This file is missing a prompt"',
+        'good.toml': 'prompt = "This one is fine"',
+      },
+    });
+
+    const loader = new FileCommandLoader(null as unknown as Config);
+    const commands = await loader.loadCommands(signal);
+
+    expect(commands).toHaveLength(1);
+    expect(commands[0].name).toBe('good');
+  });
+
+  it('handles filename edge cases correctly', async () => {
+    const userCommandsDir = getUserCommandsDir();
+    mock({
+      [userCommandsDir]: {
+        'test.v1.toml': 'prompt = "Test prompt"',
+      },
+    });
+
+    const loader = new FileCommandLoader(null as unknown as Config);
+    const commands = await loader.loadCommands(signal);
+    const command = commands[0];
+    expect(command).toBeDefined();
+    expect(command.name).toBe('test.v1');
+  });
+
+  it('handles file system errors gracefully', async () => {
+    mock({}); // Mock an empty file system
+    const loader = new FileCommandLoader(null as unknown as Config);
+    const commands = await loader.loadCommands(signal);
+    expect(commands).toHaveLength(0);
+  });
+
+  it('uses a default description if not provided', async () => {
+    const userCommandsDir = getUserCommandsDir();
+    mock({
+      [userCommandsDir]: {
+        'test.toml': 'prompt = "Test prompt"',
+      },
+    });
+
+    const loader = new FileCommandLoader(null as unknown as Config);
+    const commands = await loader.loadCommands(signal);
+    const command = commands[0];
+    expect(command).toBeDefined();
+    expect(command.description).toBe('Custom command from test.toml');
+  });
+
+  it('uses the provided description', async () => {
+    const userCommandsDir = getUserCommandsDir();
+    mock({
+      [userCommandsDir]: {
+        'test.toml': 'prompt = "Test prompt"\ndescription = "My test command"',
+      },
+    });
+
+    const loader = new FileCommandLoader(null as unknown as Config);
+    const commands = await loader.loadCommands(signal);
+    const command = commands[0];
+    expect(command).toBeDefined();
+    expect(command.description).toBe('My test command');
+  });
+
+  it('should sanitize colons in filenames to prevent namespace conflicts', async () => {
+    const userCommandsDir = getUserCommandsDir();
+    mock({
+      [userCommandsDir]: {
+        'legacy:command.toml': 'prompt = "This is a legacy command"',
+      },
+    });
+
+    const loader = new FileCommandLoader(null as unknown as Config);
+    const commands = await loader.loadCommands(signal);
+
+    expect(commands).toHaveLength(1);
+    const command = commands[0];
+    expect(command).toBeDefined();
+
+    // Verify that the ':' in the filename was replaced with an '_'
+    expect(command.name).toBe('legacy_command');
+  });
+});
diff --git a/packages/cli/src/services/FileCommandLoader.ts b/packages/cli/src/services/FileCommandLoader.ts
new file mode 100644
index 00000000..1b96cb35
--- /dev/null
+++ b/packages/cli/src/services/FileCommandLoader.ts
@@ -0,0 +1,171 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { promises as fs } from 'fs';
+import path from 'path';
+import toml from '@iarna/toml';
+import { glob } from 'glob';
+import { z } from 'zod';
+import {
+  Config,
+  getProjectCommandsDir,
+  getUserCommandsDir,
+} from '@google/gemini-cli-core';
+import { ICommandLoader } from './types.js';
+import { CommandKind, SlashCommand } from '../ui/commands/types.js';
+
+/**
+ * Defines the Zod schema for a command definition file. This serves as the
+ * single source of truth for both validation and type inference.
+ */
+const TomlCommandDefSchema = z.object({
+  prompt: z.string({
+    required_error: "The 'prompt' field is required.",
+    invalid_type_error: "The 'prompt' field must be a string.",
+  }),
+  description: z.string().optional(),
+});
+
+/**
+ * Discovers and loads custom slash commands from .toml files in both the
+ * user's global config directory and the current project's directory.
+ *
+ * This loader is responsible for:
+ * - Recursively scanning command directories.
+ * - Parsing and validating TOML files.
+ * - Adapting valid definitions into executable SlashCommand objects.
+ * - Handling file system errors and malformed files gracefully.
+ */
+export class FileCommandLoader implements ICommandLoader {
+  private readonly projectRoot: string;
+
+  constructor(private readonly config: Config | null) {
+    this.projectRoot = config?.getProjectRoot() || process.cwd();
+  }
+
+  /**
+   * Loads all commands, applying the precedence rule where project-level
+   * commands override user-level commands with the same name.
+   * @param signal An AbortSignal to cancel the loading process.
+   * @returns A promise that resolves to an array of loaded SlashCommands.
+   */
+  async loadCommands(signal: AbortSignal): Promise<SlashCommand[]> {
+    const commandMap = new Map<string, SlashCommand>();
+    const globOptions = {
+      nodir: true,
+      dot: true,
+      signal,
+    };
+
+    try {
+      // User Commands
+      const userDir = getUserCommandsDir();
+      const userFiles = await glob('**/*.toml', {
+        ...globOptions,
+        cwd: userDir,
+      });
+      const userCommandPromises = userFiles.map((file) =>
+        this.parseAndAdaptFile(path.join(userDir, file), userDir),
+      );
+      const userCommands = (await Promise.all(userCommandPromises)).filter(
+        (cmd): cmd is SlashCommand => cmd !== null,
+      );
+      for (const cmd of userCommands) {
+        commandMap.set(cmd.name, cmd);
+      }
+
+      // Project Commands (these intentionally override user commands)
+      const projectDir = getProjectCommandsDir(this.projectRoot);
+      const projectFiles = await glob('**/*.toml', {
+        ...globOptions,
+        cwd: projectDir,
+      });
+      const projectCommandPromises = projectFiles.map((file) =>
+        this.parseAndAdaptFile(path.join(projectDir, file), projectDir),
+      );
+      const projectCommands = (
+        await Promise.all(projectCommandPromises)
+      ).filter((cmd): cmd is SlashCommand => cmd !== null);
+      for (const cmd of projectCommands) {
+        commandMap.set(cmd.name, cmd);
+      }
+    } catch (error) {
+      console.error(`[FileCommandLoader] Error during file search:`, error);
+    }
+
+    return Array.from(commandMap.values());
+  }
+
+  /**
+   * Parses a single .toml file and transforms it into a SlashCommand object.
+   * @param filePath The absolute path to the .toml file.
+   * @param baseDir The root command directory for name calculation.
+   * @returns A promise resolving to a SlashCommand, or null if the file is invalid.
+   */
+  private async parseAndAdaptFile(
+    filePath: string,
+    baseDir: string,
+  ): Promise<SlashCommand | null> {
+    let fileContent: string;
+    try {
+      fileContent = await fs.readFile(filePath, 'utf-8');
+    } catch (error: unknown) {
+      console.error(
+        `[FileCommandLoader] Failed to read file ${filePath}:`,
+        error instanceof Error ? error.message : String(error),
+      );
+      return null;
+    }
+
+    let parsed: unknown;
+    try {
+      parsed = toml.parse(fileContent);
+    } catch (error: unknown) {
+      console.error(
+        `[FileCommandLoader] Failed to parse TOML file ${filePath}:`,
+        error instanceof Error ? error.message : String(error),
+      );
+      return null;
+    }
+
+    const validationResult = TomlCommandDefSchema.safeParse(parsed);
+
+    if (!validationResult.success) {
+      console.error(
+        `[FileCommandLoader] Skipping invalid command file: ${filePath}. Validation errors:`,
+        validationResult.error.flatten(),
+      );
+      return null;
+    }
+
+    const validDef = validationResult.data;
+
+    const relativePathWithExt = path.relative(baseDir, filePath);
+    const relativePath = relativePathWithExt.substring(
+      0,
+      relativePathWithExt.length - 5, // length of '.toml'
+    );
+    const commandName = relativePath
+      .split(path.sep)
+      // Sanitize each path segment to prevent ambiguity. Since ':' is our
+      // namespace separator, we replace any literal colons in filenames
+      // with underscores to avoid naming conflicts.
+      .map((segment) => segment.replaceAll(':', '_'))
+      .join(':');
+
+    return {
+      name: commandName,
+      description:
+        validDef.description ||
+        `Custom command from ${path.basename(filePath)}`,
+      kind: CommandKind.FILE,
+      action: async () => ({
+        type: 'submit_prompt',
+        content: validDef.prompt,
+      }),
+    };
+  }
+}
diff --git a/packages/cli/src/ui/commands/types.ts b/packages/cli/src/ui/commands/types.ts
index 3ffadf83..df7b2f21 100644
--- a/packages/cli/src/ui/commands/types.ts
+++ b/packages/cli/src/ui/commands/types.ts
@@ -99,12 +99,22 @@ export interface LoadHistoryActionReturn {
   clientHistory: Content[]; // The history for the generative client
 }
 
+/**
+ * The return type for a command action that should immediately submit
+ * content as a prompt to the Gemini model.
+ */
+export interface SubmitPromptActionReturn {
+  type: 'submit_prompt';
+  content: string;
+}
+
 export type SlashCommandActionReturn =
   | ToolActionReturn
   | MessageActionReturn
   | QuitActionReturn
   | OpenDialogActionReturn
-  | LoadHistoryActionReturn;
+  | LoadHistoryActionReturn
+  | SubmitPromptActionReturn;
 
 export enum CommandKind {
   BUILT_IN = 'built-in',
diff --git a/packages/cli/src/ui/hooks/slashCommandProcessor.test.ts b/packages/cli/src/ui/hooks/slashCommandProcessor.test.ts
index 32a6810e..84eeb033 100644
--- a/packages/cli/src/ui/hooks/slashCommandProcessor.test.ts
+++ b/packages/cli/src/ui/hooks/slashCommandProcessor.test.ts
@@ -14,10 +14,17 @@ vi.mock('node:process', () => ({
   },
 }));
 
-const mockLoadCommands = vi.fn();
+const mockBuiltinLoadCommands = vi.fn();
 vi.mock('../../services/BuiltinCommandLoader.js', () => ({
   BuiltinCommandLoader: vi.fn().mockImplementation(() => ({
-    loadCommands: mockLoadCommands,
+    loadCommands: mockBuiltinLoadCommands,
+  })),
+}));
+
+const mockFileLoadCommands = vi.fn();
+vi.mock('../../services/FileCommandLoader.js', () => ({
+  FileCommandLoader: vi.fn().mockImplementation(() => ({
+    loadCommands: mockFileLoadCommands,
   })),
 }));
 
@@ -28,11 +35,22 @@ vi.mock('../contexts/SessionContext.js', () => ({
 import { act, renderHook, waitFor } from '@testing-library/react';
 import { vi, describe, it, expect, beforeEach, type Mock } from 'vitest';
 import { useSlashCommandProcessor } from './slashCommandProcessor.js';
-import { SlashCommand } from '../commands/types.js';
+import { CommandKind, SlashCommand } from '../commands/types.js';
 import { Config } from '@google/gemini-cli-core';
 import { LoadedSettings } from '../../config/settings.js';
 import { MessageType } from '../types.js';
 import { BuiltinCommandLoader } from '../../services/BuiltinCommandLoader.js';
+import { FileCommandLoader } from '../../services/FileCommandLoader.js';
+
+const createTestCommand = (
+  overrides: Partial<SlashCommand>,
+  kind: CommandKind = CommandKind.BUILT_IN,
+): SlashCommand => ({
+  name: 'test',
+  description: 'a test command',
+  kind,
+  ...overrides,
+});
 
 describe('useSlashCommandProcessor', () => {
   const mockAddItem = vi.fn();
@@ -55,11 +73,17 @@ describe('useSlashCommandProcessor', () => {
   beforeEach(() => {
     vi.clearAllMocks();
     (vi.mocked(BuiltinCommandLoader) as Mock).mockClear();
-    mockLoadCommands.mockResolvedValue([]);
+    mockBuiltinLoadCommands.mockResolvedValue([]);
+    mockFileLoadCommands.mockResolvedValue([]);
   });
 
-  const setupProcessorHook = (commands: SlashCommand[] = []) => {
-    mockLoadCommands.mockResolvedValue(Object.freeze(commands));
+  const setupProcessorHook = (
+    builtinCommands: SlashCommand[] = [],
+    fileCommands: SlashCommand[] = [],
+  ) => {
+    mockBuiltinLoadCommands.mockResolvedValue(Object.freeze(builtinCommands));
+    mockFileLoadCommands.mockResolvedValue(Object.freeze(fileCommands));
+
     const { result } = renderHook(() =>
       useSlashCommandProcessor(
         mockConfig,
@@ -83,18 +107,14 @@ describe('useSlashCommandProcessor', () => {
   };
 
   describe('Initialization and Command Loading', () => {
-    it('should initialize CommandService with BuiltinCommandLoader', () => {
+    it('should initialize CommandService with all required loaders', () => {
       setupProcessorHook();
-      expect(BuiltinCommandLoader).toHaveBeenCalledTimes(1);
       expect(BuiltinCommandLoader).toHaveBeenCalledWith(mockConfig);
+      expect(FileCommandLoader).toHaveBeenCalledWith(mockConfig);
     });
 
     it('should call loadCommands and populate state after mounting', async () => {
-      const testCommand: SlashCommand = {
-        name: 'test',
-        description: 'a test command',
-        kind: 'built-in',
-      };
+      const testCommand = createTestCommand({ name: 'test' });
       const result = setupProcessorHook([testCommand]);
 
       await waitFor(() => {
@@ -102,15 +122,12 @@ describe('useSlashCommandProcessor', () => {
       });
 
       expect(result.current.slashCommands[0]?.name).toBe('test');
-      expect(mockLoadCommands).toHaveBeenCalledTimes(1);
+      expect(mockBuiltinLoadCommands).toHaveBeenCalledTimes(1);
+      expect(mockFileLoadCommands).toHaveBeenCalledTimes(1);
     });
 
     it('should provide an immutable array of commands to consumers', async () => {
-      const testCommand: SlashCommand = {
-        name: 'test',
-        description: 'a test command',
-        kind: 'built-in',
-      };
+      const testCommand = createTestCommand({ name: 'test' });
       const result = setupProcessorHook([testCommand]);
 
       await waitFor(() => {
@@ -121,13 +138,39 @@ describe('useSlashCommandProcessor', () => {
 
       expect(() => {
         // @ts-expect-error - We are intentionally testing a violation of the readonly type.
-        commands.push({
-          name: 'rogue',
-          description: 'a rogue command',
-          kind: 'built-in',
-        });
+        commands.push(createTestCommand({ name: 'rogue' }));
       }).toThrow(TypeError);
     });
+
+    it('should override built-in commands with file-based commands of the same name', async () => {
+      const builtinAction = vi.fn();
+      const fileAction = vi.fn();
+
+      const builtinCommand = createTestCommand({
+        name: 'override',
+        description: 'builtin',
+        action: builtinAction,
+      });
+      const fileCommand = createTestCommand(
+        { name: 'override', description: 'file', action: fileAction },
+        CommandKind.FILE,
+      );
+
+      const result = setupProcessorHook([builtinCommand], [fileCommand]);
+
+      await waitFor(() => {
+        // The service should only return one command with the name 'override'
+        expect(result.current.slashCommands).toHaveLength(1);
+      });
+
+      await act(async () => {
+        await result.current.handleSlashCommand('/override');
+      });
+
+      // Only the file-based command's action should be called.
+      expect(fileAction).toHaveBeenCalledTimes(1);
+      expect(builtinAction).not.toHaveBeenCalled();
+    });
   });
 
   describe('Command Execution Logic', () => {
@@ -142,10 +185,10 @@ describe('useSlashCommandProcessor', () => {
       // Expect 2 calls: one for the user's input, one for the error message.
       expect(mockAddItem).toHaveBeenCalledTimes(2);
       expect(mockAddItem).toHaveBeenLastCalledWith(
-        expect.objectContaining({
+        {
           type: MessageType.ERROR,
           text: 'Unknown command: /nonexistent',
-        }),
+        },
         expect.any(Number),
       );
     });
@@ -154,12 +197,12 @@ describe('useSlashCommandProcessor', () => {
       const parentCommand: SlashCommand = {
         name: 'parent',
         description: 'a parent command',
-        kind: 'built-in',
+        kind: CommandKind.BUILT_IN,
         subCommands: [
           {
             name: 'child1',
             description: 'First child.',
-            kind: 'built-in',
+            kind: CommandKind.BUILT_IN,
           },
         ],
       };
@@ -172,12 +215,12 @@ describe('useSlashCommandProcessor', () => {
 
       expect(mockAddItem).toHaveBeenCalledTimes(2);
       expect(mockAddItem).toHaveBeenLastCalledWith(
-        expect.objectContaining({
+        {
           type: MessageType.INFO,
           text: expect.stringContaining(
             "Command '/parent' requires a subcommand.",
           ),
-        }),
+        },
         expect.any(Number),
       );
     });
@@ -187,12 +230,12 @@ describe('useSlashCommandProcessor', () => {
       const parentCommand: SlashCommand = {
         name: 'parent',
         description: 'a parent command',
-        kind: 'built-in',
+        kind: CommandKind.BUILT_IN,
         subCommands: [
           {
             name: 'child',
             description: 'a child command',
-            kind: 'built-in',
+            kind: CommandKind.BUILT_IN,
             action: childAction,
           },
         ],
@@ -222,12 +265,10 @@ describe('useSlashCommandProcessor', () => {
 
   describe('Action Result Handling', () => {
     it('should handle "dialog: help" action', async () => {
-      const command: SlashCommand = {
+      const command = createTestCommand({
         name: 'helpcmd',
-        description: 'a help command',
-        kind: 'built-in',
         action: vi.fn().mockResolvedValue({ type: 'dialog', dialog: 'help' }),
-      };
+      });
       const result = setupProcessorHook([command]);
       await waitFor(() => expect(result.current.slashCommands).toHaveLength(1));
 
@@ -239,16 +280,14 @@ describe('useSlashCommandProcessor', () => {
     });
 
     it('should handle "load_history" action', async () => {
-      const command: SlashCommand = {
+      const command = createTestCommand({
         name: 'load',
-        description: 'a load command',
-        kind: 'built-in',
         action: vi.fn().mockResolvedValue({
           type: 'load_history',
           history: [{ type: MessageType.USER, text: 'old prompt' }],
           clientHistory: [{ role: 'user', parts: [{ text: 'old prompt' }] }],
         }),
-      };
+      });
       const result = setupProcessorHook([command]);
       await waitFor(() => expect(result.current.slashCommands).toHaveLength(1));
 
@@ -258,7 +297,7 @@ describe('useSlashCommandProcessor', () => {
 
       expect(mockClearItems).toHaveBeenCalledTimes(1);
       expect(mockAddItem).toHaveBeenCalledWith(
-        expect.objectContaining({ type: 'user', text: 'old prompt' }),
+        { type: 'user', text: 'old prompt' },
         expect.any(Number),
       );
     });
@@ -270,12 +309,10 @@ describe('useSlashCommandProcessor', () => {
         const quitAction = vi
           .fn()
           .mockResolvedValue({ type: 'quit', messages: [] });
-        const command: SlashCommand = {
+        const command = createTestCommand({
           name: 'exit',
-          description: 'an exit command',
-          kind: 'built-in',
           action: quitAction,
-        };
+        });
         const result = setupProcessorHook([command]);
 
         await waitFor(() =>
@@ -300,15 +337,43 @@ describe('useSlashCommandProcessor', () => {
         }
       });
     });
+
+    it('should handle "submit_prompt" action returned from a file-based command', async () => {
+      const fileCommand = createTestCommand(
+        {
+          name: 'filecmd',
+          description: 'A command from a file',
+          action: async () => ({
+            type: 'submit_prompt',
+            content: 'The actual prompt from the TOML file.',
+          }),
+        },
+        CommandKind.FILE,
+      );
+
+      const result = setupProcessorHook([], [fileCommand]);
+      await waitFor(() => expect(result.current.slashCommands).toHaveLength(1));
+
+      let actionResult;
+      await act(async () => {
+        actionResult = await result.current.handleSlashCommand('/filecmd');
+      });
+
+      expect(actionResult).toEqual({
+        type: 'submit_prompt',
+        content: 'The actual prompt from the TOML file.',
+      });
+
+      expect(mockAddItem).toHaveBeenCalledWith(
+        { type: MessageType.USER, text: '/filecmd' },
+        expect.any(Number),
+      );
+    });
   });
 
   describe('Command Parsing and Matching', () => {
     it('should be case-sensitive', async () => {
-      const command: SlashCommand = {
-        name: 'test',
-        description: 'a test command',
-        kind: 'built-in',
-      };
+      const command = createTestCommand({ name: 'test' });
       const result = setupProcessorHook([command]);
       await waitFor(() => expect(result.current.slashCommands).toHaveLength(1));
 
@@ -319,23 +384,22 @@ describe('useSlashCommandProcessor', () => {
 
       // It should fail and call addItem with an error
       expect(mockAddItem).toHaveBeenCalledWith(
-        expect.objectContaining({
+        {
           type: MessageType.ERROR,
           text: 'Unknown command: /Test',
-        }),
+        },
         expect.any(Number),
       );
     });
 
     it('should correctly match an altName', async () => {
       const action = vi.fn();
-      const command: SlashCommand = {
+      const command = createTestCommand({
         name: 'main',
         altNames: ['alias'],
         description: 'a command with an alias',
-        kind: 'built-in',
         action,
-      };
+      });
       const result = setupProcessorHook([command]);
       await waitFor(() => expect(result.current.slashCommands).toHaveLength(1));
 
@@ -351,12 +415,7 @@ describe('useSlashCommandProcessor', () => {
 
     it('should handle extra whitespace around the command', async () => {
       const action = vi.fn();
-      const command: SlashCommand = {
-        name: 'test',
-        description: 'a test command',
-        kind: 'built-in',
-        action,
-      };
+      const command = createTestCommand({ name: 'test', action });
       const result = setupProcessorHook([command]);
       await waitFor(() => expect(result.current.slashCommands).toHaveLength(1));
 
@@ -366,6 +425,82 @@ describe('useSlashCommandProcessor', () => {
 
       expect(action).toHaveBeenCalledWith(expect.anything(), 'with-args');
     });
+
+    it('should handle `?` as a command prefix', async () => {
+      const action = vi.fn();
+      const command = createTestCommand({ name: 'help', action });
+      const result = setupProcessorHook([command]);
+      await waitFor(() => expect(result.current.slashCommands).toHaveLength(1));
+
+      await act(async () => {
+        await result.current.handleSlashCommand('?help');
+      });
+
+      expect(action).toHaveBeenCalledTimes(1);
+    });
+  });
+
+  describe('Command Precedence', () => {
+    it('should prioritize a command with a primary name over a command with a matching alias', async () => {
+      const quitAction = vi.fn();
+      const exitAction = vi.fn();
+
+      const quitCommand = createTestCommand({
+        name: 'quit',
+        altNames: ['exit'],
+        action: quitAction,
+      });
+
+      const exitCommand = createTestCommand(
+        {
+          name: 'exit',
+          action: exitAction,
+        },
+        CommandKind.FILE,
+      );
+
+      // The order of commands in the final loaded array is not guaranteed,
+      // so the test must work regardless of which comes first.
+      const result = setupProcessorHook([quitCommand], [exitCommand]);
+
+      await waitFor(() => {
+        expect(result.current.slashCommands).toHaveLength(2);
+      });
+
+      await act(async () => {
+        await result.current.handleSlashCommand('/exit');
+      });
+
+      // The action for the command whose primary name is 'exit' should be called.
+      expect(exitAction).toHaveBeenCalledTimes(1);
+      // The action for the command that has 'exit' as an alias should NOT be called.
+      expect(quitAction).not.toHaveBeenCalled();
+    });
+
+    it('should add an overridden command to the history', async () => {
+      const quitCommand = createTestCommand({
+        name: 'quit',
+        altNames: ['exit'],
+        action: vi.fn(),
+      });
+      const exitCommand = createTestCommand(
+        { name: 'exit', action: vi.fn() },
+        CommandKind.FILE,
+      );
+
+      const result = setupProcessorHook([quitCommand], [exitCommand]);
+      await waitFor(() => expect(result.current.slashCommands).toHaveLength(2));
+
+      await act(async () => {
+        await result.current.handleSlashCommand('/exit');
+      });
+
+      // It should be added to the history.
+      expect(mockAddItem).toHaveBeenCalledWith(
+        { type: MessageType.USER, text: '/exit' },
+        expect.any(Number),
+      );
+    });
   });
 
   describe('Lifecycle', () => {
diff --git a/packages/cli/src/ui/hooks/slashCommandProcessor.ts b/packages/cli/src/ui/hooks/slashCommandProcessor.ts
index cdf071b1..48be0470 100644
--- a/packages/cli/src/ui/hooks/slashCommandProcessor.ts
+++ b/packages/cli/src/ui/hooks/slashCommandProcessor.ts
@@ -22,6 +22,7 @@ import { LoadedSettings } from '../../config/settings.js';
 import { type CommandContext, type SlashCommand } from '../commands/types.js';
 import { CommandService } from '../../services/CommandService.js';
 import { BuiltinCommandLoader } from '../../services/BuiltinCommandLoader.js';
+import { FileCommandLoader } from '../../services/FileCommandLoader.js';
 
 /**
  * Hook to define and process slash commands (e.g., /help, /clear).
@@ -162,8 +163,10 @@ export const useSlashCommandProcessor = (
   useEffect(() => {
     const controller = new AbortController();
     const load = async () => {
-      // TODO - Add other loaders for custom commands.
-      const loaders = [new BuiltinCommandLoader(config)];
+      const loaders = [
+        new BuiltinCommandLoader(config),
+        new FileCommandLoader(config),
+      ];
       const commandService = await CommandService.create(
         loaders,
         controller.signal,
@@ -192,12 +195,7 @@ export const useSlashCommandProcessor = (
       }
 
       const userMessageTimestamp = Date.now();
-      if (trimmed !== '/quit' && trimmed !== '/exit') {
-        addItem(
-          { type: MessageType.USER, text: trimmed },
-          userMessageTimestamp,
-        );
-      }
+      addItem({ type: MessageType.USER, text: trimmed }, userMessageTimestamp);
 
       const parts = trimmed.substring(1).trim().split(/\s+/);
       const commandPath = parts.filter((p) => p); // The parts of the command, e.g., ['memory', 'add']
@@ -207,9 +205,21 @@ export const useSlashCommandProcessor = (
       let pathIndex = 0;
 
       for (const part of commandPath) {
-        const foundCommand = currentCommands.find(
-          (cmd) => cmd.name === part || cmd.altNames?.includes(part),
-        );
+        // TODO: For better performance and architectural clarity, this two-pass
+        // search could be replaced. A more optimal approach would be to
+        // pre-compute a single lookup map in `CommandService.ts` that resolves
+        // all name and alias conflicts during the initial loading phase. The
+        // processor would then perform a single, fast lookup on that map.
+
+        // First pass: check for an exact match on the primary command name.
+        let foundCommand = currentCommands.find((cmd) => cmd.name === part);
+
+        // Second pass: if no primary name matches, check for an alias.
+        if (!foundCommand) {
+          foundCommand = currentCommands.find((cmd) =>
+            cmd.altNames?.includes(part),
+          );
+        }
 
         if (foundCommand) {
           commandToExecute = foundCommand;
@@ -290,6 +300,12 @@ export const useSlashCommandProcessor = (
                   process.exit(0);
                 }, 100);
                 return { type: 'handled' };
+
+              case 'submit_prompt':
+                return {
+                  type: 'submit_prompt',
+                  content: result.content,
+                };
               default: {
                 const unhandled: never = result;
                 throw new Error(`Unhandled slash command result: ${unhandled}`);
diff --git a/packages/cli/src/ui/hooks/useCompletion.integration.test.ts b/packages/cli/src/ui/hooks/useCompletion.integration.test.ts
index 02162159..840d2814 100644
--- a/packages/cli/src/ui/hooks/useCompletion.integration.test.ts
+++ b/packages/cli/src/ui/hooks/useCompletion.integration.test.ts
@@ -10,7 +10,11 @@ import { renderHook, act } from '@testing-library/react';
 import { useCompletion } from './useCompletion.js';
 import * as fs from 'fs/promises';
 import { glob } from 'glob';
-import { CommandContext, SlashCommand } from '../commands/types.js';
+import {
+  CommandContext,
+  CommandKind,
+  SlashCommand,
+} from '../commands/types.js';
 import { Config, FileDiscoveryService } from '@google/gemini-cli-core';
 
 interface MockConfig {
@@ -43,8 +47,18 @@ describe('useCompletion git-aware filtering integration', () => {
 
   const testCwd = '/test/project';
   const slashCommands = [
-    { name: 'help', description: 'Show help', action: vi.fn() },
-    { name: 'clear', description: 'Clear screen', action: vi.fn() },
+    {
+      name: 'help',
+      description: 'Show help',
+      kind: CommandKind.BUILT_IN,
+      action: vi.fn(),
+    },
+    {
+      name: 'clear',
+      description: 'Clear screen',
+      kind: CommandKind.BUILT_IN,
+      action: vi.fn(),
+    },
   ];
 
   // A minimal mock is sufficient for these tests.
@@ -56,31 +70,37 @@ describe('useCompletion git-aware filtering integration', () => {
       altNames: ['?'],
       description: 'Show help',
       action: vi.fn(),
+      kind: CommandKind.BUILT_IN,
     },
     {
       name: 'stats',
       altNames: ['usage'],
       description: 'check session stats. Usage: /stats [model|tools]',
       action: vi.fn(),
+      kind: CommandKind.BUILT_IN,
     },
     {
       name: 'clear',
       description: 'Clear the screen',
       action: vi.fn(),
+      kind: CommandKind.BUILT_IN,
     },
     {
       name: 'memory',
       description: 'Manage memory',
+      kind: CommandKind.BUILT_IN,
       // This command is a parent, no action.
       subCommands: [
         {
           name: 'show',
           description: 'Show memory',
+          kind: CommandKind.BUILT_IN,
           action: vi.fn(),
         },
         {
           name: 'add',
           description: 'Add to memory',
+          kind: CommandKind.BUILT_IN,
           action: vi.fn(),
         },
       ],
@@ -88,15 +108,18 @@ describe('useCompletion git-aware filtering integration', () => {
     {
       name: 'chat',
       description: 'Manage chat history',
+      kind: CommandKind.BUILT_IN,
       subCommands: [
         {
           name: 'save',
           description: 'Save chat',
+          kind: CommandKind.BUILT_IN,
           action: vi.fn(),
         },
         {
           name: 'resume',
           description: 'Resume a saved chat',
+          kind: CommandKind.BUILT_IN,
           action: vi.fn(),
           // This command provides its own argument completions
           completion: vi
diff --git a/packages/cli/src/ui/hooks/useCompletion.test.ts b/packages/cli/src/ui/hooks/useCompletion.test.ts
index d1b22a88..19671de4 100644
--- a/packages/cli/src/ui/hooks/useCompletion.test.ts
+++ b/packages/cli/src/ui/hooks/useCompletion.test.ts
@@ -12,7 +12,11 @@ import { renderHook, act } from '@testing-library/react';
 import { useCompletion } from './useCompletion.js';
 import * as fs from 'fs/promises';
 import { glob } from 'glob';
-import { CommandContext, SlashCommand } from '../commands/types.js';
+import {
+  CommandContext,
+  CommandKind,
+  SlashCommand,
+} from '../commands/types.js';
 import { Config, FileDiscoveryService } from '@google/gemini-cli-core';
 
 // Mock dependencies
@@ -69,30 +73,36 @@ describe('useCompletion', () => {
         altNames: ['?'],
         description: 'Show help',
         action: vi.fn(),
+        kind: CommandKind.BUILT_IN,
       },
       {
         name: 'stats',
         altNames: ['usage'],
         description: 'check session stats. Usage: /stats [model|tools]',
         action: vi.fn(),
+        kind: CommandKind.BUILT_IN,
       },
       {
         name: 'clear',
         description: 'Clear the screen',
         action: vi.fn(),
+        kind: CommandKind.BUILT_IN,
       },
       {
         name: 'memory',
         description: 'Manage memory',
+        kind: CommandKind.BUILT_IN,
         subCommands: [
           {
             name: 'show',
             description: 'Show memory',
+            kind: CommandKind.BUILT_IN,
             action: vi.fn(),
           },
           {
             name: 'add',
             description: 'Add to memory',
+            kind: CommandKind.BUILT_IN,
             action: vi.fn(),
           },
         ],
@@ -100,15 +110,20 @@ describe('useCompletion', () => {
       {
         name: 'chat',
         description: 'Manage chat history',
+        kind: CommandKind.BUILT_IN,
         subCommands: [
           {
             name: 'save',
             description: 'Save chat',
+            kind: CommandKind.BUILT_IN,
+
             action: vi.fn(),
           },
           {
             name: 'resume',
             description: 'Resume a saved chat',
+            kind: CommandKind.BUILT_IN,
+
             action: vi.fn(),
             completion: vi.fn().mockResolvedValue(['chat1', 'chat2']),
           },
@@ -344,6 +359,7 @@ describe('useCompletion', () => {
       const largeMockCommands = Array.from({ length: 15 }, (_, i) => ({
         name: `command${i}`,
         description: `Command ${i}`,
+        kind: CommandKind.BUILT_IN,
         action: vi.fn(),
       }));
 
@@ -629,6 +645,88 @@ describe('useCompletion', () => {
     });
   });
 
+  describe('Slash command completion with namespaced names', () => {
+    let commandsWithNamespaces: SlashCommand[];
+
+    beforeEach(() => {
+      commandsWithNamespaces = [
+        ...mockSlashCommands,
+        {
+          name: 'git:commit',
+          description: 'A namespaced git command',
+          kind: CommandKind.FILE,
+          action: vi.fn(),
+        },
+        {
+          name: 'git:push',
+          description: 'Another namespaced git command',
+          kind: CommandKind.FILE,
+          action: vi.fn(),
+        },
+        {
+          name: 'docker:build',
+          description: 'A docker command',
+          kind: CommandKind.FILE,
+          action: vi.fn(),
+        },
+      ];
+    });
+
+    it('should suggest a namespaced command based on a partial match', () => {
+      const { result } = renderHook(() =>
+        useCompletion(
+          '/git:co',
+          testCwd,
+          true,
+          commandsWithNamespaces,
+          mockCommandContext,
+          mockConfig,
+        ),
+      );
+
+      expect(result.current.suggestions).toHaveLength(1);
+      expect(result.current.suggestions[0].label).toBe('git:commit');
+    });
+
+    it('should suggest all commands within a namespace when the namespace prefix is typed', () => {
+      const { result } = renderHook(() =>
+        useCompletion(
+          '/git:',
+          testCwd,
+          true,
+          commandsWithNamespaces,
+          mockCommandContext,
+          mockConfig,
+        ),
+      );
+
+      expect(result.current.suggestions).toHaveLength(2);
+      expect(result.current.suggestions.map((s) => s.label)).toEqual(
+        expect.arrayContaining(['git:commit', 'git:push']),
+      );
+
+      expect(result.current.suggestions.map((s) => s.label)).not.toContain(
+        'docker:build',
+      );
+    });
+
+    it('should not provide suggestions if the namespaced command is a perfect leaf match', () => {
+      const { result } = renderHook(() =>
+        useCompletion(
+          '/git:commit',
+          testCwd,
+          true,
+          commandsWithNamespaces,
+          mockCommandContext,
+          mockConfig,
+        ),
+      );
+
+      expect(result.current.showSuggestions).toBe(false);
+      expect(result.current.suggestions).toHaveLength(0);
+    });
+  });
+
   describe('File path completion (@-syntax)', () => {
     beforeEach(() => {
       vi.mocked(fs.readdir).mockResolvedValue([
diff --git a/packages/cli/src/ui/hooks/useGeminiStream.test.tsx b/packages/cli/src/ui/hooks/useGeminiStream.test.tsx
index d7fd35c8..02fae607 100644
--- a/packages/cli/src/ui/hooks/useGeminiStream.test.tsx
+++ b/packages/cli/src/ui/hooks/useGeminiStream.test.tsx
@@ -1058,6 +1058,65 @@ describe('useGeminiStream', () => {
         expect(mockSendMessageStream).not.toHaveBeenCalled(); // No LLM call made
       });
     });
+
+    it('should call Gemini with prompt content when slash command returns a `submit_prompt` action', async () => {
+      const customCommandResult: SlashCommandProcessorResult = {
+        type: 'submit_prompt',
+        content: 'This is the actual prompt from the command file.',
+      };
+      mockHandleSlashCommand.mockResolvedValue(customCommandResult);
+
+      const { result, mockSendMessageStream: localMockSendMessageStream } =
+        renderTestHook();
+
+      await act(async () => {
+        await result.current.submitQuery('/my-custom-command');
+      });
+
+      await waitFor(() => {
+        expect(mockHandleSlashCommand).toHaveBeenCalledWith(
+          '/my-custom-command',
+        );
+
+        expect(localMockSendMessageStream).not.toHaveBeenCalledWith(
+          '/my-custom-command',
+          expect.anything(),
+          expect.anything(),
+        );
+
+        expect(localMockSendMessageStream).toHaveBeenCalledWith(
+          'This is the actual prompt from the command file.',
+          expect.any(AbortSignal),
+          expect.any(String),
+        );
+
+        expect(mockScheduleToolCalls).not.toHaveBeenCalled();
+      });
+    });
+
+    it('should correctly handle a submit_prompt action with empty content', async () => {
+      const emptyPromptResult: SlashCommandProcessorResult = {
+        type: 'submit_prompt',
+        content: '',
+      };
+      mockHandleSlashCommand.mockResolvedValue(emptyPromptResult);
+
+      const { result, mockSendMessageStream: localMockSendMessageStream } =
+        renderTestHook();
+
+      await act(async () => {
+        await result.current.submitQuery('/emptycmd');
+      });
+
+      await waitFor(() => {
+        expect(mockHandleSlashCommand).toHaveBeenCalledWith('/emptycmd');
+        expect(localMockSendMessageStream).toHaveBeenCalledWith(
+          '',
+          expect.any(AbortSignal),
+          expect.any(String),
+        );
+      });
+    });
   });
 
   describe('Memory Refresh on save_memory', () => {
diff --git a/packages/cli/src/ui/hooks/useGeminiStream.ts b/packages/cli/src/ui/hooks/useGeminiStream.ts
index 295b5650..456c0fb7 100644
--- a/packages/cli/src/ui/hooks/useGeminiStream.ts
+++ b/packages/cli/src/ui/hooks/useGeminiStream.ts
@@ -240,19 +240,37 @@ export const useGeminiStream = (
         const slashCommandResult = await handleSlashCommand(trimmedQuery);
 
         if (slashCommandResult) {
-          if (slashCommandResult.type === 'schedule_tool') {
-            const { toolName, toolArgs } = slashCommandResult;
-            const toolCallRequest: ToolCallRequestInfo = {
-              callId: `${toolName}-${Date.now()}-${Math.random().toString(16).slice(2)}`,
-              name: toolName,
-              args: toolArgs,
-              isClientInitiated: true,
-              prompt_id,
-            };
-            scheduleToolCalls([toolCallRequest], abortSignal);
-          }
+          switch (slashCommandResult.type) {
+            case 'schedule_tool': {
+              const { toolName, toolArgs } = slashCommandResult;
+              const toolCallRequest: ToolCallRequestInfo = {
+                callId: `${toolName}-${Date.now()}-${Math.random().toString(16).slice(2)}`,
+                name: toolName,
+                args: toolArgs,
+                isClientInitiated: true,
+                prompt_id,
+              };
+              scheduleToolCalls([toolCallRequest], abortSignal);
+              return { queryToSend: null, shouldProceed: false };
+            }
+            case 'submit_prompt': {
+              localQueryToSendToGemini = slashCommandResult.content;
 
-          return { queryToSend: null, shouldProceed: false };
+              return {
+                queryToSend: localQueryToSendToGemini,
+                shouldProceed: true,
+              };
+            }
+            case 'handled': {
+              return { queryToSend: null, shouldProceed: false };
+            }
+            default: {
+              const unreachable: never = slashCommandResult;
+              throw new Error(
+                `Unhandled slash command result type: ${unreachable}`,
+              );
+            }
+          }
         }
 
         if (shellModeActive && handleShellCommand(trimmedQuery, abortSignal)) {
diff --git a/packages/cli/src/ui/types.ts b/packages/cli/src/ui/types.ts
index 223ccd47..da95d6ec 100644
--- a/packages/cli/src/ui/types.ts
+++ b/packages/cli/src/ui/types.ts
@@ -218,6 +218,15 @@ export interface ConsoleMessageItem {
 }
 
 /**
+ * Result type for a slash command that should immediately result in a prompt
+ * being submitted to the Gemini model.
+ */
+export interface SubmitPromptResult {
+  type: 'submit_prompt';
+  content: string;
+}
+
+/**
  * Defines the result of the slash command processor for its consumer (useGeminiStream).
  */
 export type SlashCommandProcessorResult =
@@ -228,4 +237,5 @@ export type SlashCommandProcessorResult =
     }
   | {
       type: 'handled'; // Indicates the command was processed and no further action is needed.
-    };
+    }
+  | SubmitPromptResult;
diff --git a/packages/cli/tsconfig.json b/packages/cli/tsconfig.json
index c0faa166..55be9a03 100644
--- a/packages/cli/tsconfig.json
+++ b/packages/cli/tsconfig.json
@@ -3,7 +3,7 @@
   "compilerOptions": {
     "outDir": "dist",
     "jsx": "react-jsx",
-    "lib": ["DOM", "DOM.Iterable", "ES2020"],
+    "lib": ["DOM", "DOM.Iterable", "ES2022"],
     "types": ["node", "vitest/globals"]
   },
   "include": [
diff --git a/packages/core/src/utils/paths.ts b/packages/core/src/utils/paths.ts
index 3382c588..5370a7cb 100644
--- a/packages/core/src/utils/paths.ts
+++ b/packages/core/src/utils/paths.ts
@@ -11,6 +11,7 @@ import * as crypto from 'crypto';
 export const GEMINI_DIR = '.gemini';
 export const GOOGLE_ACCOUNTS_FILENAME = 'google_accounts.json';
 const TMP_DIR_NAME = 'tmp';
+const COMMANDS_DIR_NAME = 'commands';
 
 /**
  * Replaces the home directory with a tilde.
@@ -158,3 +159,20 @@ export function getProjectTempDir(projectRoot: string): string {
   const hash = getProjectHash(projectRoot);
   return path.join(os.homedir(), GEMINI_DIR, TMP_DIR_NAME, hash);
 }
+
+/**
+ * Returns the absolute path to the user-level commands directory.
+ * @returns The path to the user's commands directory.
+ */
+export function getUserCommandsDir(): string {
+  return path.join(os.homedir(), GEMINI_DIR, COMMANDS_DIR_NAME);
+}
+
+/**
+ * Returns the absolute path to the project-level commands directory.
+ * @param projectRoot The absolute path to the project's root directory.
+ * @returns The path to the project's commands directory.
+ */
+export function getProjectCommandsDir(projectRoot: string): string {
+  return path.join(projectRoot, GEMINI_DIR, COMMANDS_DIR_NAME);
+}