feat: Implement CLI and model memory management (#371)

Co-authored-by: N. Taylor Mullen <[email protected]>

11 files changed, 940 insertions, 42 deletions

diff --git a/packages/cli/src/config/config.ts b/packages/cli/src/config/config.ts
index c0ec38af..9f03bee4 100644
--- a/packages/cli/src/config/config.ts
+++ b/packages/cli/src/config/config.ts
@@ -15,6 +15,8 @@ import {
   Config,
   loadEnvironment,
   createServerConfig,
+  GEMINI_CONFIG_DIR,
+  GEMINI_MD_FILENAME,
 } from '@gemini-code/server';
 import { Settings } from './settings.js';
 import { readPackageUp } from 'read-package-up';
@@ -30,8 +32,6 @@ const logger = {
 };
 
 const DEFAULT_GEMINI_MODEL = 'gemini-2.5-pro-preview-05-06';
-const GEMINI_MD_FILENAME = 'GEMINI.md';
-const GEMINI_CONFIG_DIR = '.gemini';
 // TODO(adh): Refactor to use a shared ignore list with other tools like glob and read-many-files.
 const DEFAULT_IGNORE_DIRECTORIES = [
   'node_modules',
diff --git a/packages/cli/src/config/memoryUtils.ts b/packages/cli/src/config/memoryUtils.ts
new file mode 100644
index 00000000..d44b5ebf
--- /dev/null
+++ b/packages/cli/src/config/memoryUtils.ts
@@ -0,0 +1,163 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import * as fs from 'fs/promises';
+import * as path from 'path';
+import { homedir } from 'os';
+import { SETTINGS_DIRECTORY_NAME } from './settings.js';
+import {
+  getErrorMessage,
+  MemoryTool,
+  GEMINI_MD_FILENAME,
+  MEMORY_SECTION_HEADER,
+} from '@gemini-code/server';
+
+/**
+ * Gets the absolute path to the global GEMINI.md file.
+ */
+export function getGlobalMemoryFilePath(): string {
+  return path.join(homedir(), SETTINGS_DIRECTORY_NAME, GEMINI_MD_FILENAME);
+}
+
+/**
+ * Adds a new memory entry to the global GEMINI.md file under the specified header.
+ */
+export async function addMemoryEntry(text: string): Promise<void> {
+  const filePath = getGlobalMemoryFilePath();
+  // The performAddMemoryEntry method from MemoryTool will handle its own errors
+  // and throw an appropriately formatted error if needed.
+  await MemoryTool.performAddMemoryEntry(text, filePath, {
+    readFile: fs.readFile,
+    writeFile: fs.writeFile,
+    mkdir: fs.mkdir,
+  });
+}
+
+/**
+ * Deletes the last added memory entry from the "Gemini Added Memories" section.
+ */
+export async function deleteLastMemoryEntry(): Promise<boolean> {
+  const filePath = getGlobalMemoryFilePath();
+  try {
+    let content = await fs.readFile(filePath, 'utf-8');
+    const headerIndex = content.indexOf(MEMORY_SECTION_HEADER);
+
+    if (headerIndex === -1) return false; // Section not found
+
+    const startOfSectionContent = headerIndex + MEMORY_SECTION_HEADER.length;
+    let endOfSectionIndex = content.indexOf('\n## ', startOfSectionContent);
+    if (endOfSectionIndex === -1) {
+      endOfSectionIndex = content.length;
+    }
+
+    const sectionPart = content.substring(
+      startOfSectionContent,
+      endOfSectionIndex,
+    );
+    const lines = sectionPart.split(/\r?\n/).map((line) => line.trimEnd());
+
+    let lastBulletLineIndex = -1;
+    for (let i = lines.length - 1; i >= 0; i--) {
+      if (lines[i].trim().startsWith('- ')) {
+        lastBulletLineIndex = i;
+        break;
+      }
+    }
+
+    if (lastBulletLineIndex === -1) return false; // No bullets found in section
+
+    lines.splice(lastBulletLineIndex, 1);
+
+    const newSectionPart = lines
+      .filter((line) => line.trim().length > 0)
+      .join('\n');
+
+    const beforeHeader = content.substring(0, headerIndex);
+    const afterSection = content.substring(endOfSectionIndex);
+
+    if (newSectionPart.trim().length === 0) {
+      // If section is now empty (no bullets), remove header too or leave it clean
+      // For simplicity, let's leave the header but ensure it has a newline after if content follows
+      content = `${beforeHeader}${MEMORY_SECTION_HEADER}\n${afterSection}`
+        .replace(/\n{3,}/g, '\n\n')
+        .trimEnd();
+      if (content.length > 0) content += '\n';
+    } else {
+      content =
+        `${beforeHeader}${MEMORY_SECTION_HEADER}\n${newSectionPart}\n${afterSection}`
+          .replace(/\n{3,}/g, '\n\n')
+          .trimEnd();
+      if (content.length > 0) content += '\n';
+    }
+
+    await fs.writeFile(filePath, content, 'utf-8');
+    return true;
+  } catch (error) {
+    if (error instanceof Error && 'code' in error && error.code === 'ENOENT') {
+      return false;
+    }
+    console.error(`Error deleting last memory entry from ${filePath}:`, error);
+    throw new Error(
+      `Failed to delete last memory entry: ${getErrorMessage(error)}`,
+    );
+  }
+}
+
+/**
+ * Deletes all added memory entries (the entire "Gemini Added Memories" section).
+ */
+export async function deleteAllAddedMemoryEntries(): Promise<number> {
+  const filePath = getGlobalMemoryFilePath();
+  try {
+    let content = await fs.readFile(filePath, 'utf-8');
+    const headerIndex = content.indexOf(MEMORY_SECTION_HEADER);
+
+    if (headerIndex === -1) return 0; // Section not found
+
+    let endOfSectionIndex = content.indexOf(
+      '\n## ',
+      headerIndex + MEMORY_SECTION_HEADER.length,
+    );
+    if (endOfSectionIndex === -1) {
+      endOfSectionIndex = content.length; // Section goes to EOF
+    }
+
+    const sectionContent = content.substring(headerIndex, endOfSectionIndex);
+    const bulletCount = (sectionContent.match(/\n- /g) || []).length;
+
+    if (bulletCount === 0 && !sectionContent.includes('- ')) {
+      // No bullets found
+      // If we only remove if bullets exist, or remove header if no bullets.
+      // For now, if header exists but no bullets, consider 0 deleted if we only count bullets.
+      // If the goal is to remove the section if it exists, this logic changes.
+      // Let's assume we only care about bulleted items for the count.
+    }
+
+    // Remove the section including the header
+    const beforeHeader = content.substring(0, headerIndex);
+    const afterSection = content.substring(endOfSectionIndex);
+
+    content = (
+      beforeHeader.trimEnd() +
+      (afterSection.length > 0 ? '\n' + afterSection.trimStart() : '')
+    ).trim();
+    if (content.length > 0) content += '\n';
+
+    await fs.writeFile(filePath, content, 'utf-8');
+    return bulletCount; // This counts '\n- ' occurrences, might need refinement for exact bullet count
+  } catch (error) {
+    if (error instanceof Error && 'code' in error && error.code === 'ENOENT') {
+      return 0;
+    }
+    console.error(
+      `Error deleting all added memory entries from ${filePath}:`,
+      error,
+    );
+    throw new Error(
+      `Failed to delete all added memory entries: ${getErrorMessage(error)}`,
+    );
+  }
+}
diff --git a/packages/cli/src/ui/hooks/slashCommandProcessor.test.ts b/packages/cli/src/ui/hooks/slashCommandProcessor.test.ts
new file mode 100644
index 00000000..4055dfd3
--- /dev/null
+++ b/packages/cli/src/ui/hooks/slashCommandProcessor.test.ts
@@ -0,0 +1,248 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+const { mockProcessExit } = vi.hoisted(() => ({
+  mockProcessExit: vi.fn((_code?: number): never => undefined as never),
+}));
+
+vi.mock('node:process', () => ({
+  exit: mockProcessExit,
+  cwd: vi.fn(() => '/mock/cwd'),
+}));
+
+vi.mock('node:fs/promises', () => ({
+  readFile: vi.fn(),
+  writeFile: vi.fn(),
+  mkdir: vi.fn(),
+}));
+
+import { act, renderHook } from '@testing-library/react';
+import { vi, describe, it, expect, beforeEach, Mock } from 'vitest';
+import { useSlashCommandProcessor } from './slashCommandProcessor.js';
+import { MessageType } from '../types.js';
+import * as memoryUtils from '../../config/memoryUtils.js';
+import { type Config, MemoryTool } from '@gemini-code/server';
+import * as fsPromises from 'node:fs/promises';
+
+// Import the module for mocking its functions
+import * as ShowMemoryCommandModule from './useShowMemoryCommand.js';
+
+// Mock dependencies
+vi.mock('./useShowMemoryCommand.js', () => ({
+  SHOW_MEMORY_COMMAND_NAME: '/memory show',
+  createShowMemoryAction: vi.fn(() => vi.fn()),
+}));
+
+// Spy on the static method we want to mock
+const performAddMemoryEntrySpy = vi.spyOn(MemoryTool, 'performAddMemoryEntry');
+
+describe('useSlashCommandProcessor', () => {
+  let mockAddItem: ReturnType<typeof vi.fn>;
+  let mockClearItems: ReturnType<typeof vi.fn>;
+  let mockRefreshStatic: ReturnType<typeof vi.fn>;
+  let mockSetShowHelp: ReturnType<typeof vi.fn>;
+  let mockOnDebugMessage: ReturnType<typeof vi.fn>;
+  let mockOpenThemeDialog: ReturnType<typeof vi.fn>;
+  let mockPerformMemoryRefresh: ReturnType<typeof vi.fn>;
+  let mockConfig: Config;
+
+  beforeEach(() => {
+    mockAddItem = vi.fn();
+    mockClearItems = vi.fn();
+    mockRefreshStatic = vi.fn();
+    mockSetShowHelp = vi.fn();
+    mockOnDebugMessage = vi.fn();
+    mockOpenThemeDialog = vi.fn();
+    mockPerformMemoryRefresh = vi.fn().mockResolvedValue(undefined);
+    mockConfig = { getDebugMode: vi.fn(() => false) } as unknown as Config;
+
+    // Clear mocks for fsPromises if they were used directly or indirectly
+    vi.mocked(fsPromises.readFile).mockClear();
+    vi.mocked(fsPromises.writeFile).mockClear();
+    vi.mocked(fsPromises.mkdir).mockClear();
+
+    performAddMemoryEntrySpy.mockReset(); // Reset the spy
+    vi.spyOn(memoryUtils, 'deleteLastMemoryEntry').mockImplementation(vi.fn());
+    vi.spyOn(memoryUtils, 'deleteAllAddedMemoryEntries').mockImplementation(
+      vi.fn(),
+    );
+
+    vi.mocked(memoryUtils.deleteLastMemoryEntry).mockClear();
+    vi.mocked(memoryUtils.deleteAllAddedMemoryEntries).mockClear();
+
+    mockProcessExit.mockClear();
+    (ShowMemoryCommandModule.createShowMemoryAction as Mock).mockClear();
+    mockPerformMemoryRefresh.mockClear();
+  });
+
+  const getProcessor = () => {
+    const { result } = renderHook(() =>
+      useSlashCommandProcessor(
+        mockConfig,
+        mockAddItem,
+        mockClearItems,
+        mockRefreshStatic,
+        mockSetShowHelp,
+        mockOnDebugMessage,
+        mockOpenThemeDialog,
+        mockPerformMemoryRefresh,
+      ),
+    );
+    return result.current;
+  };
+
+  describe('/memory add', () => {
+    it('should call MemoryTool.performAddMemoryEntry and refresh on valid input', async () => {
+      performAddMemoryEntrySpy.mockResolvedValue(undefined);
+      const { handleSlashCommand } = getProcessor();
+      const fact = 'Remember this fact';
+      await act(async () => {
+        handleSlashCommand(`/memory add ${fact}`);
+      });
+      expect(mockAddItem).toHaveBeenNthCalledWith(
+        1,
+        expect.objectContaining({
+          type: MessageType.USER,
+          text: `/memory add ${fact}`,
+        }),
+        expect.any(Number),
+      );
+      expect(performAddMemoryEntrySpy).toHaveBeenCalledWith(
+        fact,
+        memoryUtils.getGlobalMemoryFilePath(), // Ensure this path is correct
+        {
+          readFile: fsPromises.readFile,
+          writeFile: fsPromises.writeFile,
+          mkdir: fsPromises.mkdir,
+        },
+      );
+      expect(mockPerformMemoryRefresh).toHaveBeenCalled();
+      expect(mockAddItem).toHaveBeenNthCalledWith(
+        2,
+        expect.objectContaining({
+          type: MessageType.INFO,
+          text: `Successfully added to memory: "${fact}"`,
+        }),
+        expect.any(Number),
+      );
+    });
+
+    it('should show usage error if no text is provided', async () => {
+      const { handleSlashCommand } = getProcessor();
+      await act(async () => {
+        handleSlashCommand('/memory add ');
+      });
+      expect(performAddMemoryEntrySpy).not.toHaveBeenCalled();
+      expect(mockAddItem).toHaveBeenNthCalledWith(
+        2,
+        expect.objectContaining({
+          type: MessageType.ERROR,
+          text: 'Usage: /memory add <text to remember>',
+        }),
+        expect.any(Number),
+      );
+    });
+
+    it('should handle error from MemoryTool.performAddMemoryEntry', async () => {
+      const fact = 'Another fact';
+      performAddMemoryEntrySpy.mockRejectedValue(
+        new Error('[MemoryTool] Failed to add memory entry: Disk full'),
+      );
+      const { handleSlashCommand } = getProcessor();
+      await act(async () => {
+        handleSlashCommand(`/memory add ${fact}`);
+      });
+      expect(performAddMemoryEntrySpy).toHaveBeenCalledWith(
+        fact,
+        memoryUtils.getGlobalMemoryFilePath(),
+        {
+          readFile: fsPromises.readFile,
+          writeFile: fsPromises.writeFile,
+          mkdir: fsPromises.mkdir,
+        },
+      );
+      expect(mockAddItem).toHaveBeenNthCalledWith(
+        2,
+        expect.objectContaining({
+          type: MessageType.ERROR,
+          text: 'Failed to add memory: [MemoryTool] Failed to add memory entry: Disk full',
+        }),
+        expect.any(Number),
+      );
+    });
+  });
+
+  describe('/memory show', () => {
+    it('should call the showMemoryAction', async () => {
+      const mockReturnedShowAction = vi.fn();
+      vi.mocked(ShowMemoryCommandModule.createShowMemoryAction).mockReturnValue(
+        mockReturnedShowAction,
+      );
+      const { handleSlashCommand } = getProcessor();
+      await act(async () => {
+        handleSlashCommand('/memory show');
+      });
+      expect(
+        ShowMemoryCommandModule.createShowMemoryAction,
+      ).toHaveBeenCalledWith(mockConfig, expect.any(Function));
+      expect(mockReturnedShowAction).toHaveBeenCalled();
+    });
+  });
+
+  describe('/memory refresh', () => {
+    it('should call performMemoryRefresh', async () => {
+      const { handleSlashCommand } = getProcessor();
+      await act(async () => {
+        handleSlashCommand('/memory refresh');
+      });
+      expect(mockPerformMemoryRefresh).toHaveBeenCalled();
+    });
+  });
+
+  describe('Unknown /memory subcommand', () => {
+    it('should show an error for unknown /memory subcommand', async () => {
+      const { handleSlashCommand } = getProcessor();
+      await act(async () => {
+        handleSlashCommand('/memory foobar');
+      });
+      expect(mockAddItem).toHaveBeenNthCalledWith(
+        2,
+        expect.objectContaining({
+          type: MessageType.ERROR,
+          text: 'Unknown /memory command: foobar. Available: show, refresh, add',
+        }),
+        expect.any(Number),
+      );
+    });
+  });
+
+  describe('Other commands', () => {
+    it('/help should open help', async () => {
+      const { handleSlashCommand } = getProcessor();
+      await act(async () => {
+        handleSlashCommand('/help');
+      });
+      expect(mockSetShowHelp).toHaveBeenCalledWith(true);
+    });
+  });
+
+  describe('Unknown command', () => {
+    it('should show an error for a general unknown command', async () => {
+      const { handleSlashCommand } = getProcessor();
+      await act(async () => {
+        handleSlashCommand('/unknowncommand');
+      });
+      expect(mockAddItem).toHaveBeenNthCalledWith(
+        2,
+        expect.objectContaining({
+          type: MessageType.ERROR,
+          text: 'Unknown command: /unknowncommand',
+        }),
+        expect.any(Number),
+      );
+    });
+  });
+});
diff --git a/packages/cli/src/ui/hooks/slashCommandProcessor.ts b/packages/cli/src/ui/hooks/slashCommandProcessor.ts
index efe6d855..f489c648 100644
--- a/packages/cli/src/ui/hooks/slashCommandProcessor.ts
+++ b/packages/cli/src/ui/hooks/slashCommandProcessor.ts
@@ -6,22 +6,17 @@
 
 import { useCallback, useMemo } from 'react';
 import { type PartListUnion } from '@google/genai';
-import { getCommandFromQuery } from '../utils/commandUtils.js';
 import { UseHistoryManagerReturn } from './useHistoryManager.js';
-import { Config } from '@gemini-code/server'; // Import Config
-import { Message, MessageType, HistoryItemWithoutId } from '../types.js'; // Import Message types
-import {
-  createShowMemoryAction,
-  SHOW_MEMORY_COMMAND_NAME,
-} from './useShowMemoryCommand.js';
-import { REFRESH_MEMORY_COMMAND_NAME } from './useRefreshMemoryCommand.js'; // Only import name now
-import process from 'node:process'; // For process.exit
+import { Config } from '@gemini-code/server';
+import { Message, MessageType, HistoryItemWithoutId } from '../types.js';
+import { createShowMemoryAction } from './useShowMemoryCommand.js';
+import { addMemoryEntry } from '../../config/memoryUtils.js';
 
 export interface SlashCommand {
   name: string;
   altName?: string;
   description: string;
-  action: (value: PartListUnion | string) => void; // Allow string for simpler actions
+  action: (mainCommand: string, subCommand?: string, args?: string) => void;
 }
 
 /**
@@ -54,13 +49,43 @@ export const useSlashCommandProcessor = (
     await actionFn();
   }, [config, addMessage]);
 
+  const addMemoryAction = useCallback(
+    async (_mainCommand: string, _subCommand?: string, args?: string) => {
+      if (!args || args.trim() === '') {
+        addMessage({
+          type: MessageType.ERROR,
+          content: 'Usage: /memory add <text to remember>',
+          timestamp: new Date(),
+        });
+        return;
+      }
+      try {
+        await addMemoryEntry(args);
+        addMessage({
+          type: MessageType.INFO,
+          content: `Successfully added to memory: "${args}"`,
+          timestamp: new Date(),
+        });
+        await performMemoryRefresh(); // Refresh memory to reflect changes
+      } catch (e) {
+        const errorMessage = e instanceof Error ? e.message : String(e);
+        addMessage({
+          type: MessageType.ERROR,
+          content: `Failed to add memory: ${errorMessage}`,
+          timestamp: new Date(),
+        });
+      }
+    },
+    [addMessage, performMemoryRefresh],
+  );
+
   const slashCommands: SlashCommand[] = useMemo(
     () => [
       {
         name: 'help',
         altName: '?',
         description: 'for help on gemini-code',
-        action: (_value: PartListUnion | string) => {
+        action: (_mainCommand, _subCommand, _args) => {
           onDebugMessage('Opening help.');
           setShowHelp(true);
         },
@@ -68,7 +93,7 @@ export const useSlashCommandProcessor = (
       {
         name: 'clear',
         description: 'clear the screen',
-        action: (_value: PartListUnion | string) => {
+        action: (_mainCommand, _subCommand, _args) => {
           onDebugMessage('Clearing terminal.');
           clearItems();
           console.clear();
@@ -78,25 +103,39 @@ export const useSlashCommandProcessor = (
       {
         name: 'theme',
         description: 'change the theme',
-        action: (_value) => {
+        action: (_mainCommand, _subCommand, _args) => {
           openThemeDialog();
         },
       },
       {
-        name: REFRESH_MEMORY_COMMAND_NAME.substring(1), // Remove leading '/'
-        description: 'Reloads instructions from all GEMINI.md files.',
-        action: performMemoryRefresh, // Use the passed in function
-      },
-      {
-        name: SHOW_MEMORY_COMMAND_NAME.substring(1), // Remove leading '/'
-        description: 'Displays the current hierarchical memory content.',
-        action: showMemoryAction,
+        name: 'memory',
+        description:
+          'Manage memory. Usage: /memory <show|refresh|add|delete_last|delete_all_added> [text for add]',
+        action: (mainCommand, subCommand, args) => {
+          switch (subCommand) {
+            case 'show':
+              showMemoryAction();
+              break;
+            case 'refresh':
+              performMemoryRefresh();
+              break;
+            case 'add':
+              addMemoryAction(mainCommand, subCommand, args);
+              break;
+            default:
+              addMessage({
+                type: MessageType.ERROR,
+                content: `Unknown /memory command: ${subCommand}. Available: show, refresh, add`,
+                timestamp: new Date(),
+              });
+          }
+        },
       },
       {
         name: 'quit',
         altName: 'exit',
         description: 'exit the cli',
-        action: (_value: PartListUnion | string) => {
+        action: (_mainCommand, _subCommand, _args) => {
           onDebugMessage('Quitting. Good-bye.');
           process.exit(0);
         },
@@ -108,8 +147,10 @@ export const useSlashCommandProcessor = (
       refreshStatic,
       openThemeDialog,
       clearItems,
-      performMemoryRefresh, // Add to dependencies
+      performMemoryRefresh,
       showMemoryAction,
+      addMemoryAction,
+      addMessage,
     ],
   );
 
@@ -120,36 +161,51 @@ export const useSlashCommandProcessor = (
       }
 
       const trimmed = rawQuery.trim();
-      const [symbol, test] = getCommandFromQuery(trimmed);
 
-      if (symbol !== '/' && symbol !== '?') {
+      if (!trimmed.startsWith('/') && !trimmed.startsWith('?')) {
         return false;
       }
 
       const userMessageTimestamp = Date.now();
-      // Add user message to history only if it's not a silent command or handled internally
-      // For now, adding all slash commands to history for transparency.
+
       addItem({ type: MessageType.USER, text: trimmed }, userMessageTimestamp);
 
+      let subCommand: string | undefined;
+      let args: string | undefined;
+
+      const commandToMatch = (() => {
+        if (trimmed.startsWith('?')) {
+          return 'help'; // No subCommand or args for '?' acting as help
+        }
+        // For other slash commands like /memory add foo
+        const parts = trimmed.substring(1).trim().split(/\s+/);
+        if (parts.length > 1) {
+          subCommand = parts[1];
+        }
+        if (parts.length > 2) {
+          args = parts.slice(2).join(' ');
+        }
+        return parts[0]; // This is the main command name
+      })();
+
+      const mainCommand = commandToMatch;
+
       for (const cmd of slashCommands) {
-        if (
-          test === cmd.name ||
-          test === cmd.altName ||
-          (symbol === '?' && cmd.altName === '?') // Special handling for ? as help
-        ) {
-          cmd.action(trimmed); // Pass the full trimmed command for context if needed
+        if (mainCommand === cmd.name || mainCommand === cmd.altName) {
+          cmd.action(mainCommand, subCommand, args);
           return true;
         }
       }
 
-      addItem(
-        { type: MessageType.ERROR, text: `Unknown command: ${trimmed}` },
-        userMessageTimestamp,
-      );
+      addMessage({
+        type: MessageType.ERROR,
+        content: `Unknown command: ${trimmed}`,
+        timestamp: new Date(),
+      });
 
       return true;
     },
-    [addItem, slashCommands],
+    [addItem, slashCommands, addMessage],
   );
 
   return { handleSlashCommand, slashCommands };
diff --git a/packages/server/src/config/config.ts b/packages/server/src/config/config.ts
index 4221b71e..8b9648c4 100644
--- a/packages/server/src/config/config.ts
+++ b/packages/server/src/config/config.ts
@@ -20,6 +20,7 @@ import { WriteFileTool } from '../tools/write-file.js';
 import { WebFetchTool } from '../tools/web-fetch.js';
 import { ReadManyFilesTool } from '../tools/read-many-files.js';
 import { BaseTool, ToolResult } from '../tools/tools.js';
+import { MemoryTool } from '../tools/memoryTool.js';
 import { StdioServerParameters } from '@modelcontextprotocol/sdk/client/stdio.js';
 
 export class Config {
@@ -188,9 +189,10 @@ function createToolRegistry(config: Config): ToolRegistry {
     new GlobTool(targetDir),
     new EditTool(config),
     new WriteFileTool(targetDir),
-    new WebFetchTool(), // Note: WebFetchTool takes no arguments
+    new WebFetchTool(),
     new ReadManyFilesTool(targetDir),
     new ShellTool(config),
+    new MemoryTool(),
   ];
 
   for (const tool of tools) {
diff --git a/packages/server/src/core/__snapshots__/prompts.test.ts.snap b/packages/server/src/core/__snapshots__/prompts.test.ts.snap
index 8305ee00..b824d4f7 100644
--- a/packages/server/src/core/__snapshots__/prompts.test.ts.snap
+++ b/packages/server/src/core/__snapshots__/prompts.test.ts.snap
@@ -65,6 +65,7 @@ Rigorously adhere to existing project conventions when reading or modifying code
 -   **Command Execution:** Use the 'execute_bash_command' tool for running shell commands, remembering the safety rule to explain modifying commands first.
 -   **Background Processes:** Use background processes (via \`&\`) for commands that are unlikely to stop on their own, e.g. \`node server.js &\`. If unsure, ask the user.
 -   **Interactive Commands:** Try to avoid shell commands that are likely to require user interaction (e.g. \`git rebase -i\`). Use non-interactive versions of commands (e.g. \`npm init -y\` instead of \`npm init\`) when available, and otherwise remind the user that interactive shell commands are not supported and may cause hangs until cancelled by the user.
+-   **Remembering Facts:** Use the 'saveMemory' tool to remember specific, *user-related* facts or preferences when the user explicitly asks, or when they state a clear, concise piece of information that would help personalize or streamline *your future interactions with them* (e.g., preferred coding style, common project paths they use, personal tool aliases). This tool is for user-specific information that should persist across sessions. Do *not* use it for general project context or information that belongs in project-specific \`GEMINI.md\` files. If unsure whether to save something, you can ask the user, "Should I remember that for you?"
 
 ## Interaction Details
 -   **Help Command:** The user can use '/help' to display help information.
@@ -218,6 +219,7 @@ Rigorously adhere to existing project conventions when reading or modifying code
 -   **Command Execution:** Use the 'execute_bash_command' tool for running shell commands, remembering the safety rule to explain modifying commands first.
 -   **Background Processes:** Use background processes (via \`&\`) for commands that are unlikely to stop on their own, e.g. \`node server.js &\`. If unsure, ask the user.
 -   **Interactive Commands:** Try to avoid shell commands that are likely to require user interaction (e.g. \`git rebase -i\`). Use non-interactive versions of commands (e.g. \`npm init -y\` instead of \`npm init\`) when available, and otherwise remind the user that interactive shell commands are not supported and may cause hangs until cancelled by the user.
+-   **Remembering Facts:** Use the 'saveMemory' tool to remember specific, *user-related* facts or preferences when the user explicitly asks, or when they state a clear, concise piece of information that would help personalize or streamline *your future interactions with them* (e.g., preferred coding style, common project paths they use, personal tool aliases). This tool is for user-specific information that should persist across sessions. Do *not* use it for general project context or information that belongs in project-specific \`GEMINI.md\` files. If unsure whether to save something, you can ask the user, "Should I remember that for you?"
 
 ## Interaction Details
 -   **Help Command:** The user can use '/help' to display help information.
@@ -366,6 +368,7 @@ Rigorously adhere to existing project conventions when reading or modifying code
 -   **Command Execution:** Use the 'execute_bash_command' tool for running shell commands, remembering the safety rule to explain modifying commands first.
 -   **Background Processes:** Use background processes (via \`&\`) for commands that are unlikely to stop on their own, e.g. \`node server.js &\`. If unsure, ask the user.
 -   **Interactive Commands:** Try to avoid shell commands that are likely to require user interaction (e.g. \`git rebase -i\`). Use non-interactive versions of commands (e.g. \`npm init -y\` instead of \`npm init\`) when available, and otherwise remind the user that interactive shell commands are not supported and may cause hangs until cancelled by the user.
+-   **Remembering Facts:** Use the 'saveMemory' tool to remember specific, *user-related* facts or preferences when the user explicitly asks, or when they state a clear, concise piece of information that would help personalize or streamline *your future interactions with them* (e.g., preferred coding style, common project paths they use, personal tool aliases). This tool is for user-specific information that should persist across sessions. Do *not* use it for general project context or information that belongs in project-specific \`GEMINI.md\` files. If unsure whether to save something, you can ask the user, "Should I remember that for you?"
 
 ## Interaction Details
 -   **Help Command:** The user can use '/help' to display help information.
@@ -514,6 +517,7 @@ Rigorously adhere to existing project conventions when reading or modifying code
 -   **Command Execution:** Use the 'execute_bash_command' tool for running shell commands, remembering the safety rule to explain modifying commands first.
 -   **Background Processes:** Use background processes (via \`&\`) for commands that are unlikely to stop on their own, e.g. \`node server.js &\`. If unsure, ask the user.
 -   **Interactive Commands:** Try to avoid shell commands that are likely to require user interaction (e.g. \`git rebase -i\`). Use non-interactive versions of commands (e.g. \`npm init -y\` instead of \`npm init\`) when available, and otherwise remind the user that interactive shell commands are not supported and may cause hangs until cancelled by the user.
+-   **Remembering Facts:** Use the 'saveMemory' tool to remember specific, *user-related* facts or preferences when the user explicitly asks, or when they state a clear, concise piece of information that would help personalize or streamline *your future interactions with them* (e.g., preferred coding style, common project paths they use, personal tool aliases). This tool is for user-specific information that should persist across sessions. Do *not* use it for general project context or information that belongs in project-specific \`GEMINI.md\` files. If unsure whether to save something, you can ask the user, "Should I remember that for you?"
 
 ## Interaction Details
 -   **Help Command:** The user can use '/help' to display help information.
@@ -662,6 +666,7 @@ Rigorously adhere to existing project conventions when reading or modifying code
 -   **Command Execution:** Use the 'execute_bash_command' tool for running shell commands, remembering the safety rule to explain modifying commands first.
 -   **Background Processes:** Use background processes (via \`&\`) for commands that are unlikely to stop on their own, e.g. \`node server.js &\`. If unsure, ask the user.
 -   **Interactive Commands:** Try to avoid shell commands that are likely to require user interaction (e.g. \`git rebase -i\`). Use non-interactive versions of commands (e.g. \`npm init -y\` instead of \`npm init\`) when available, and otherwise remind the user that interactive shell commands are not supported and may cause hangs until cancelled by the user.
+-   **Remembering Facts:** Use the 'saveMemory' tool to remember specific, *user-related* facts or preferences when the user explicitly asks, or when they state a clear, concise piece of information that would help personalize or streamline *your future interactions with them* (e.g., preferred coding style, common project paths they use, personal tool aliases). This tool is for user-specific information that should persist across sessions. Do *not* use it for general project context or information that belongs in project-specific \`GEMINI.md\` files. If unsure whether to save something, you can ask the user, "Should I remember that for you?"
 
 ## Interaction Details
 -   **Help Command:** The user can use '/help' to display help information.
@@ -810,6 +815,7 @@ Rigorously adhere to existing project conventions when reading or modifying code
 -   **Command Execution:** Use the 'execute_bash_command' tool for running shell commands, remembering the safety rule to explain modifying commands first.
 -   **Background Processes:** Use background processes (via \`&\`) for commands that are unlikely to stop on their own, e.g. \`node server.js &\`. If unsure, ask the user.
 -   **Interactive Commands:** Try to avoid shell commands that are likely to require user interaction (e.g. \`git rebase -i\`). Use non-interactive versions of commands (e.g. \`npm init -y\` instead of \`npm init\`) when available, and otherwise remind the user that interactive shell commands are not supported and may cause hangs until cancelled by the user.
+-   **Remembering Facts:** Use the 'saveMemory' tool to remember specific, *user-related* facts or preferences when the user explicitly asks, or when they state a clear, concise piece of information that would help personalize or streamline *your future interactions with them* (e.g., preferred coding style, common project paths they use, personal tool aliases). This tool is for user-specific information that should persist across sessions. Do *not* use it for general project context or information that belongs in project-specific \`GEMINI.md\` files. If unsure whether to save something, you can ask the user, "Should I remember that for you?"
 
 ## Interaction Details
 -   **Help Command:** The user can use '/help' to display help information.
@@ -958,6 +964,7 @@ Rigorously adhere to existing project conventions when reading or modifying code
 -   **Command Execution:** Use the 'execute_bash_command' tool for running shell commands, remembering the safety rule to explain modifying commands first.
 -   **Background Processes:** Use background processes (via \`&\`) for commands that are unlikely to stop on their own, e.g. \`node server.js &\`. If unsure, ask the user.
 -   **Interactive Commands:** Try to avoid shell commands that are likely to require user interaction (e.g. \`git rebase -i\`). Use non-interactive versions of commands (e.g. \`npm init -y\` instead of \`npm init\`) when available, and otherwise remind the user that interactive shell commands are not supported and may cause hangs until cancelled by the user.
+-   **Remembering Facts:** Use the 'saveMemory' tool to remember specific, *user-related* facts or preferences when the user explicitly asks, or when they state a clear, concise piece of information that would help personalize or streamline *your future interactions with them* (e.g., preferred coding style, common project paths they use, personal tool aliases). This tool is for user-specific information that should persist across sessions. Do *not* use it for general project context or information that belongs in project-specific \`GEMINI.md\` files. If unsure whether to save something, you can ask the user, "Should I remember that for you?"
 
 ## Interaction Details
 -   **Help Command:** The user can use '/help' to display help information.
diff --git a/packages/server/src/core/prompts.ts b/packages/server/src/core/prompts.ts
index 40a56a2a..d21c78fe 100644
--- a/packages/server/src/core/prompts.ts
+++ b/packages/server/src/core/prompts.ts
@@ -14,6 +14,7 @@ import { ShellTool } from '../tools/shell.js';
 import { WriteFileTool } from '../tools/write-file.js';
 import process from 'node:process'; // Import process
 import { execSync } from 'node:child_process';
+import { MemoryTool } from '../tools/memoryTool.js';
 
 const contactEmail = '[email protected]';
 
@@ -82,6 +83,7 @@ Rigorously adhere to existing project conventions when reading or modifying code
 -   **Command Execution:** Use the '${ShellTool.Name}' tool for running shell commands, remembering the safety rule to explain modifying commands first.
 -   **Background Processes:** Use background processes (via \`&\`) for commands that are unlikely to stop on their own, e.g. \`node server.js &\`. If unsure, ask the user.
 -   **Interactive Commands:** Try to avoid shell commands that are likely to require user interaction (e.g. \`git rebase -i\`). Use non-interactive versions of commands (e.g. \`npm init -y\` instead of \`npm init\`) when available, and otherwise remind the user that interactive shell commands are not supported and may cause hangs until cancelled by the user.
+-   **Remembering Facts:** Use the '${MemoryTool.Name}' tool to remember specific, *user-related* facts or preferences when the user explicitly asks, or when they state a clear, concise piece of information that would help personalize or streamline *your future interactions with them* (e.g., preferred coding style, common project paths they use, personal tool aliases). This tool is for user-specific information that should persist across sessions. Do *not* use it for general project context or information that belongs in project-specific \`GEMINI.md\` files. If unsure whether to save something, you can ask the user, "Should I remember that for you?"
 
 ## Interaction Details
 -   **Help Command:** The user can use '/help' to display help information.
diff --git a/packages/server/src/index.ts b/packages/server/src/index.ts
index a1ebc571..9183c2f9 100644
--- a/packages/server/src/index.ts
+++ b/packages/server/src/index.ts
@@ -32,3 +32,4 @@ export * from './tools/glob.js';
 export * from './tools/edit.js';
 export * from './tools/write-file.js';
 export * from './tools/web-fetch.js';
+export * from './tools/memoryTool.js';
diff --git a/packages/server/src/tools/memoryTool.test.ts b/packages/server/src/tools/memoryTool.test.ts
new file mode 100644
index 00000000..efbbb025
--- /dev/null
+++ b/packages/server/src/tools/memoryTool.test.ts
@@ -0,0 +1,224 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { vi, describe, it, expect, beforeEach, afterEach, Mock } from 'vitest';
+import { MemoryTool } from './memoryTool.js';
+import * as fs from 'fs/promises';
+import * as path from 'path';
+import * as os from 'os';
+
+// Mock dependencies
+vi.mock('fs/promises');
+vi.mock('os');
+
+const MEMORY_SECTION_HEADER = '## Gemini Added Memories';
+
+// Define a type for our fsAdapter to ensure consistency
+interface FsAdapter {
+  readFile: (path: string, encoding: 'utf-8') => Promise<string>;
+  writeFile: (path: string, data: string, encoding: 'utf-8') => Promise<void>;
+  mkdir: (
+    path: string,
+    options: { recursive: boolean },
+  ) => Promise<string | undefined>;
+}
+
+describe('MemoryTool', () => {
+  const mockAbortSignal = new AbortController().signal;
+
+  const mockFsAdapter: {
+    readFile: Mock<FsAdapter['readFile']>;
+    writeFile: Mock<FsAdapter['writeFile']>;
+    mkdir: Mock<FsAdapter['mkdir']>;
+  } = {
+    readFile: vi.fn(),
+    writeFile: vi.fn(),
+    mkdir: vi.fn(),
+  };
+
+  beforeEach(() => {
+    vi.mocked(os.homedir).mockReturnValue('/mock/home');
+    mockFsAdapter.readFile.mockReset();
+    mockFsAdapter.writeFile.mockReset().mockResolvedValue(undefined);
+    mockFsAdapter.mkdir
+      .mockReset()
+      .mockResolvedValue(undefined as string | undefined);
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  describe('performAddMemoryEntry (static method)', () => {
+    const testFilePath = path.join('/mock/home', '.gemini', 'GEMINI.md');
+
+    it('should create section and save a fact if file does not exist', async () => {
+      mockFsAdapter.readFile.mockRejectedValue({ code: 'ENOENT' }); // Simulate file not found
+      const fact = 'The sky is blue';
+      await MemoryTool.performAddMemoryEntry(fact, testFilePath, mockFsAdapter);
+
+      expect(mockFsAdapter.mkdir).toHaveBeenCalledWith(
+        path.dirname(testFilePath),
+        {
+          recursive: true,
+        },
+      );
+      expect(mockFsAdapter.writeFile).toHaveBeenCalledOnce();
+      const writeFileCall = mockFsAdapter.writeFile.mock.calls[0];
+      expect(writeFileCall[0]).toBe(testFilePath);
+      const expectedContent = `${MEMORY_SECTION_HEADER}\n- ${fact}\n`;
+      expect(writeFileCall[1]).toBe(expectedContent);
+      expect(writeFileCall[2]).toBe('utf-8');
+    });
+
+    it('should create section and save a fact if file is empty', async () => {
+      mockFsAdapter.readFile.mockResolvedValue(''); // Simulate empty file
+      const fact = 'The sky is blue';
+      await MemoryTool.performAddMemoryEntry(fact, testFilePath, mockFsAdapter);
+      const writeFileCall = mockFsAdapter.writeFile.mock.calls[0];
+      const expectedContent = `${MEMORY_SECTION_HEADER}\n- ${fact}\n`;
+      expect(writeFileCall[1]).toBe(expectedContent);
+    });
+
+    it('should add a fact to an existing section', async () => {
+      const initialContent = `Some preamble.\n\n${MEMORY_SECTION_HEADER}\n- Existing fact 1\n`;
+      mockFsAdapter.readFile.mockResolvedValue(initialContent);
+      const fact = 'New fact 2';
+      await MemoryTool.performAddMemoryEntry(fact, testFilePath, mockFsAdapter);
+
+      expect(mockFsAdapter.writeFile).toHaveBeenCalledOnce();
+      const writeFileCall = mockFsAdapter.writeFile.mock.calls[0];
+      const expectedContent = `Some preamble.\n\n${MEMORY_SECTION_HEADER}\n- Existing fact 1\n- ${fact}\n`;
+      expect(writeFileCall[1]).toBe(expectedContent);
+    });
+
+    it('should add a fact to an existing empty section', async () => {
+      const initialContent = `Some preamble.\n\n${MEMORY_SECTION_HEADER}\n`; // Empty section
+      mockFsAdapter.readFile.mockResolvedValue(initialContent);
+      const fact = 'First fact in section';
+      await MemoryTool.performAddMemoryEntry(fact, testFilePath, mockFsAdapter);
+
+      expect(mockFsAdapter.writeFile).toHaveBeenCalledOnce();
+      const writeFileCall = mockFsAdapter.writeFile.mock.calls[0];
+      const expectedContent = `Some preamble.\n\n${MEMORY_SECTION_HEADER}\n- ${fact}\n`;
+      expect(writeFileCall[1]).toBe(expectedContent);
+    });
+
+    it('should add a fact when other ## sections exist and preserve spacing', async () => {
+      const initialContent = `${MEMORY_SECTION_HEADER}\n- Fact 1\n\n## Another Section\nSome other text.`;
+      mockFsAdapter.readFile.mockResolvedValue(initialContent);
+      const fact = 'Fact 2';
+      await MemoryTool.performAddMemoryEntry(fact, testFilePath, mockFsAdapter);
+
+      expect(mockFsAdapter.writeFile).toHaveBeenCalledOnce();
+      const writeFileCall = mockFsAdapter.writeFile.mock.calls[0];
+      // Note: The implementation ensures a single newline at the end if content exists.
+      const expectedContent = `${MEMORY_SECTION_HEADER}\n- Fact 1\n- ${fact}\n\n## Another Section\nSome other text.\n`;
+      expect(writeFileCall[1]).toBe(expectedContent);
+    });
+
+    it('should correctly trim and add a fact that starts with a dash', async () => {
+      mockFsAdapter.readFile.mockResolvedValue(`${MEMORY_SECTION_HEADER}\n`);
+      const fact = '- - My fact with dashes';
+      await MemoryTool.performAddMemoryEntry(fact, testFilePath, mockFsAdapter);
+      const writeFileCall = mockFsAdapter.writeFile.mock.calls[0];
+      const expectedContent = `${MEMORY_SECTION_HEADER}\n- My fact with dashes\n`;
+      expect(writeFileCall[1]).toBe(expectedContent);
+    });
+
+    it('should handle error from fsAdapter.writeFile', async () => {
+      mockFsAdapter.readFile.mockResolvedValue('');
+      mockFsAdapter.writeFile.mockRejectedValue(new Error('Disk full'));
+      const fact = 'This will fail';
+      await expect(
+        MemoryTool.performAddMemoryEntry(fact, testFilePath, mockFsAdapter),
+      ).rejects.toThrow('[MemoryTool] Failed to add memory entry: Disk full');
+    });
+  });
+
+  describe('execute (instance method)', () => {
+    let memoryTool: MemoryTool;
+    let performAddMemoryEntrySpy: Mock<typeof MemoryTool.performAddMemoryEntry>;
+
+    beforeEach(() => {
+      memoryTool = new MemoryTool();
+      // Spy on the static method for these tests
+      performAddMemoryEntrySpy = vi
+        .spyOn(MemoryTool, 'performAddMemoryEntry')
+        .mockResolvedValue(undefined) as Mock<
+        typeof MemoryTool.performAddMemoryEntry
+      >;
+      // Cast needed as spyOn returns MockInstance
+    });
+
+    it('should have correct name, displayName, description, and schema', () => {
+      expect(memoryTool.name).toBe('saveMemory');
+      expect(memoryTool.displayName).toBe('Save Memory');
+      expect(memoryTool.description).toContain(
+        'Saves a specific piece of information',
+      );
+      expect(memoryTool.schema).toBeDefined();
+      expect(memoryTool.schema.name).toBe('saveMemory');
+      expect(memoryTool.schema.parameters?.properties?.fact).toBeDefined();
+    });
+
+    it('should call performAddMemoryEntry with correct parameters and return success', async () => {
+      const params = { fact: 'The sky is blue' };
+      const result = await memoryTool.execute(params, mockAbortSignal);
+      const expectedFilePath = path.join('/mock/home', '.gemini', 'GEMINI.md');
+
+      // For this test, we expect the actual fs methods to be passed
+      const expectedFsArgument = {
+        readFile: fs.readFile,
+        writeFile: fs.writeFile,
+        mkdir: fs.mkdir,
+      };
+
+      expect(performAddMemoryEntrySpy).toHaveBeenCalledWith(
+        params.fact,
+        expectedFilePath,
+        expectedFsArgument,
+      );
+      const successMessage = `Okay, I've remembered that: "${params.fact}"`;
+      expect(result.llmContent).toBe(
+        JSON.stringify({ success: true, message: successMessage }),
+      );
+      expect(result.returnDisplay).toBe(successMessage);
+    });
+
+    it('should return an error if fact is empty', async () => {
+      const params = { fact: ' ' }; // Empty fact
+      const result = await memoryTool.execute(params, mockAbortSignal);
+      const errorMessage = 'Parameter "fact" must be a non-empty string.';
+
+      expect(performAddMemoryEntrySpy).not.toHaveBeenCalled();
+      expect(result.llmContent).toBe(
+        JSON.stringify({ success: false, error: errorMessage }),
+      );
+      expect(result.returnDisplay).toBe(`Error: ${errorMessage}`);
+    });
+
+    it('should handle errors from performAddMemoryEntry', async () => {
+      const params = { fact: 'This will fail' };
+      const underlyingError = new Error(
+        '[MemoryTool] Failed to add memory entry: Disk full',
+      );
+      performAddMemoryEntrySpy.mockRejectedValue(underlyingError);
+
+      const result = await memoryTool.execute(params, mockAbortSignal);
+
+      expect(result.llmContent).toBe(
+        JSON.stringify({
+          success: false,
+          error: `Failed to save memory. Detail: ${underlyingError.message}`,
+        }),
+      );
+      expect(result.returnDisplay).toBe(
+        `Error saving memory: ${underlyingError.message}`,
+      );
+    });
+  });
+});
diff --git a/packages/server/src/tools/memoryTool.ts b/packages/server/src/tools/memoryTool.ts
new file mode 100644
index 00000000..177072fe
--- /dev/null
+++ b/packages/server/src/tools/memoryTool.ts
@@ -0,0 +1,194 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { BaseTool, ToolResult } from './tools.js';
+import * as fs from 'fs/promises';
+import * as path from 'path';
+import { homedir } from 'os';
+
+const memoryToolSchemaData = {
+  name: 'saveMemory',
+  description:
+    'Saves a specific piece of information or fact to your long-term memory. Use this when the user explicitly asks you to remember something, or when they state a clear, concise fact that seems important to retain for future interactions.',
+  parameters: {
+    type: 'object',
+    properties: {
+      fact: {
+        type: 'string',
+        description:
+          'The specific fact or piece of information to remember. Should be a clear, self-contained statement.',
+      },
+    },
+    required: ['fact'],
+  },
+};
+
+const memoryToolDescription = `
+Saves a specific piece of information or fact to your long-term memory.
+
+Use this tool:
+
+- When the user explicitly asks you to remember something (e.g., "Remember that I like pineapple on pizza", "Please save this: my cat's name is Whiskers").
+- When the user states a clear, concise fact about themselves, their preferences, or their environment that seems important for you to retain for future interactions to provide a more personalized and effective assistance.
+
+Do NOT use this tool:
+
+- To remember conversational context that is only relevant for the current session.
+- To save long, complex, or rambling pieces of text. The fact should be relatively short and to the point.
+- If you are unsure whether the information is a fact worth remembering long-term. If in doubt, you can ask the user, "Should I remember that for you?"
+
+## Parameters
+
+- \`fact\` (string, required): The specific fact or piece of information to remember. This should be a clear, self-contained statement. For example, if the user says "My favorite color is blue", the fact would be "My favorite color is blue".
+`;
+
+export const GEMINI_CONFIG_DIR = '.gemini';
+export const GEMINI_MD_FILENAME = 'GEMINI.md';
+export const MEMORY_SECTION_HEADER = '## Gemini Added Memories';
+
+interface SaveMemoryParams {
+  fact: string;
+}
+
+function getGlobalMemoryFilePath(): string {
+  return path.join(homedir(), GEMINI_CONFIG_DIR, GEMINI_MD_FILENAME);
+}
+
+/**
+ * Ensures proper newline separation before appending content.
+ */
+function ensureNewlineSeparation(currentContent: string): string {
+  if (currentContent.length === 0) return '';
+  if (currentContent.endsWith('\n\n') || currentContent.endsWith('\r\n\r\n'))
+    return '';
+  if (currentContent.endsWith('\n') || currentContent.endsWith('\r\n'))
+    return '\n';
+  return '\n\n';
+}
+
+export class MemoryTool extends BaseTool<SaveMemoryParams, ToolResult> {
+  static readonly Name: string = memoryToolSchemaData.name;
+  constructor() {
+    super(
+      MemoryTool.Name,
+      'Save Memory',
+      memoryToolDescription,
+      memoryToolSchemaData.parameters as Record<string, unknown>,
+    );
+  }
+
+  static async performAddMemoryEntry(
+    text: string,
+    memoryFilePath: string,
+    fsAdapter: {
+      readFile: (path: string, encoding: 'utf-8') => Promise<string>;
+      writeFile: (
+        path: string,
+        data: string,
+        encoding: 'utf-8',
+      ) => Promise<void>;
+      mkdir: (
+        path: string,
+        options: { recursive: boolean },
+      ) => Promise<string | undefined>;
+    },
+  ): Promise<void> {
+    let processedText = text.trim();
+    // Remove leading hyphens and spaces that might be misinterpreted as markdown list items
+    processedText = processedText.replace(/^(-+\s*)+/, '').trim();
+    const newMemoryItem = `- ${processedText}`;
+
+    try {
+      await fsAdapter.mkdir(path.dirname(memoryFilePath), { recursive: true });
+      let content = '';
+      try {
+        content = await fsAdapter.readFile(memoryFilePath, 'utf-8');
+      } catch (_e) {
+        // File doesn't exist, will be created with header and item.
+      }
+
+      const headerIndex = content.indexOf(MEMORY_SECTION_HEADER);
+
+      if (headerIndex === -1) {
+        // Header not found, append header and then the entry
+        const separator = ensureNewlineSeparation(content);
+        content += `${separator}${MEMORY_SECTION_HEADER}\n${newMemoryItem}\n`;
+      } else {
+        // Header found, find where to insert the new memory entry
+        const startOfSectionContent =
+          headerIndex + MEMORY_SECTION_HEADER.length;
+        let endOfSectionIndex = content.indexOf('\n## ', startOfSectionContent);
+        if (endOfSectionIndex === -1) {
+          endOfSectionIndex = content.length; // End of file
+        }
+
+        const beforeSectionMarker = content
+          .substring(0, startOfSectionContent)
+          .trimEnd();
+        let sectionContent = content
+          .substring(startOfSectionContent, endOfSectionIndex)
+          .trimEnd();
+        const afterSectionMarker = content.substring(endOfSectionIndex);
+
+        sectionContent += `\n${newMemoryItem}`;
+        content =
+          `${beforeSectionMarker}\n${sectionContent.trimStart()}\n${afterSectionMarker}`.trimEnd() +
+          '\n';
+      }
+      await fsAdapter.writeFile(memoryFilePath, content, 'utf-8');
+    } catch (error) {
+      console.error(
+        `[MemoryTool] Error adding memory entry to ${memoryFilePath}:`,
+        error,
+      );
+      throw new Error(
+        `[MemoryTool] Failed to add memory entry: ${error instanceof Error ? error.message : String(error)}`,
+      );
+    }
+  }
+
+  async execute(
+    params: SaveMemoryParams,
+    _signal: AbortSignal,
+  ): Promise<ToolResult> {
+    const { fact } = params;
+
+    if (!fact || typeof fact !== 'string' || fact.trim() === '') {
+      const errorMessage = 'Parameter "fact" must be a non-empty string.';
+      return {
+        llmContent: JSON.stringify({ success: false, error: errorMessage }),
+        returnDisplay: `Error: ${errorMessage}`,
+      };
+    }
+
+    try {
+      // Use the static method with actual fs promises
+      await MemoryTool.performAddMemoryEntry(fact, getGlobalMemoryFilePath(), {
+        readFile: fs.readFile,
+        writeFile: fs.writeFile,
+        mkdir: fs.mkdir,
+      });
+      const successMessage = `Okay, I've remembered that: "${fact}"`;
+      return {
+        llmContent: JSON.stringify({ success: true, message: successMessage }),
+        returnDisplay: successMessage,
+      };
+    } catch (error) {
+      const errorMessage =
+        error instanceof Error ? error.message : String(error);
+      console.error(
+        `[MemoryTool] Error executing saveMemory for fact "${fact}": ${errorMessage}`,
+      );
+      return {
+        llmContent: JSON.stringify({
+          success: false,
+          error: `Failed to save memory. Detail: ${errorMessage}`,
+        }),
+        returnDisplay: `Error saving memory: ${errorMessage}`,
+      };
+    }
+  }
+}
diff --git a/packages/server/src/tools/read-many-files.ts b/packages/server/src/tools/read-many-files.ts
index f424d561..4d9d35e8 100644
--- a/packages/server/src/tools/read-many-files.ts
+++ b/packages/server/src/tools/read-many-files.ts
@@ -10,6 +10,7 @@ import { getErrorMessage } from '../utils/errors.js';
 import * as fs from 'fs/promises';
 import * as path from 'path';
 import fg from 'fast-glob';
+import { GEMINI_MD_FILENAME } from './memoryTool.js';
 
 /**
  * Parameters for the ReadManyFilesTool.
@@ -100,7 +101,7 @@ const DEFAULT_EXCLUDES: string[] = [
   '**/*.odp',
   '**/*.DS_Store',
   '**/.env',
-  '**/GEMINI.md',
+  `**/${GEMINI_MD_FILENAME}`,
 ];
 
 // Default values for encoding and separator format