Add support for `.geminiignore` file (#757)

11 files changed, 408 insertions, 13 deletions

diff --git a/package-lock.json b/package-lock.json
index fe7291bf..3810490f 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -14,6 +14,7 @@
         "gemini": "bundle/gemini.js"
       },
       "devDependencies": {
+        "@types/micromatch": "^4.0.9",
         "@types/mime-types": "^2.1.4",
         "@types/minimatch": "^5.1.2",
         "@vitest/coverage-v8": "^3.1.1",
@@ -1542,6 +1543,13 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/@types/braces": {
+      "version": "3.0.5",
+      "resolved": "https://registry.npmjs.org/@types/braces/-/braces-3.0.5.tgz",
+      "integrity": "sha512-SQFof9H+LXeWNz8wDe7oN5zu7ket0qwMu5vZubW4GCJ8Kkeh6nBWUz87+KTz/G3Kqsrp0j/W253XJb3KMEeg3w==",
+      "dev": true,
+      "license": "MIT"
+    },
     "node_modules/@types/chai": {
       "version": "5.2.2",
       "resolved": "https://registry.npmjs.org/@types/chai/-/chai-5.2.2.tgz",
@@ -1615,6 +1623,16 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/@types/micromatch": {
+      "version": "4.0.9",
+      "resolved": "https://registry.npmjs.org/@types/micromatch/-/micromatch-4.0.9.tgz",
+      "integrity": "sha512-7V+8ncr22h4UoYRLnLXSpTxjQrNUXtWHGeMPRJt1nULXI57G9bIcpyrHlmrQ7QK24EyyuXvYcSSWAM8GA9nqCg==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@types/braces": "*"
+      }
+    },
     "node_modules/@types/mime-types": {
       "version": "2.1.4",
       "resolved": "https://registry.npmjs.org/@types/mime-types/-/mime-types-2.1.4.tgz",
diff --git a/package.json b/package.json
index 44e784ad..af6cacee 100644
--- a/package.json
+++ b/package.json
@@ -45,6 +45,7 @@
     "LICENSE"
   ],
   "devDependencies": {
+    "@types/micromatch": "^4.0.9",
     "@types/mime-types": "^2.1.4",
     "@types/minimatch": "^5.1.2",
     "@vitest/coverage-v8": "^3.1.1",
diff --git a/packages/cli/src/config/config.ts b/packages/cli/src/config/config.ts
index 952ecbcf..dd55b26d 100644
--- a/packages/cli/src/config/config.ts
+++ b/packages/cli/src/config/config.ts
@@ -123,6 +123,7 @@ export interface LoadCliConfigResult {
 
 export async function loadCliConfig(
   settings: Settings,
+  geminiIgnorePatterns: string[],
 ): Promise<LoadCliConfigResult> {
   loadEnvironment();
 
@@ -211,6 +212,7 @@ export async function loadCliConfig(
     vertexai: useVertexAI,
     showMemoryUsage:
       argv.show_memory_usage || settings.showMemoryUsage || false,
+    geminiIgnorePatterns,
     accessibility: settings.accessibility,
     // Git-aware file filtering settings
     fileFilteringRespectGitIgnore: settings.fileFiltering?.respectGitIgnore,
diff --git a/packages/cli/src/gemini.tsx b/packages/cli/src/gemini.tsx
index fc42bdec..f9b73074 100644
--- a/packages/cli/src/gemini.tsx
+++ b/packages/cli/src/gemini.tsx
@@ -17,6 +17,7 @@ import { LoadedSettings, loadSettings } from './config/settings.js';
 import { themeManager } from './ui/themes/theme-manager.js';
 import { getStartupWarnings } from './utils/startupWarnings.js';
 import { runNonInteractive } from './nonInteractiveCli.js';
+import { loadGeminiIgnorePatterns } from './utils/loadIgnorePatterns.js';
 import {
   ApprovalMode,
   Config,
@@ -56,9 +57,12 @@ async function main() {
       process.env.GEMINI_CODE_SANDBOX_IMAGE; // Corrected to GEMINI_SANDBOX_IMAGE_NAME
   }
 
-  const settings = loadSettings(process.cwd());
+  const workspaceRoot = process.cwd();
+  const settings = loadSettings(workspaceRoot);
+  const geminiIgnorePatterns = loadGeminiIgnorePatterns(workspaceRoot);
+
   const { config, modelWasSwitched, originalModelBeforeSwitch, finalModel } =
-    await loadCliConfig(settings.merged);
+    await loadCliConfig(settings.merged, geminiIgnorePatterns);
 
   // Initialize centralized FileDiscoveryService
   await config.getFileService();
@@ -150,6 +154,7 @@ main().catch((error) => {
   }
   process.exit(1);
 });
+
 async function loadNonInteractiveConfig(
   config: Config,
   settings: LoadedSettings,
@@ -185,6 +190,7 @@ async function loadNonInteractiveConfig(
   };
   const nonInteractiveConfigResult = await loadCliConfig(
     nonInteractiveSettings,
+    config.getGeminiIgnorePatterns(),
   );
   return nonInteractiveConfigResult.config;
 }
diff --git a/packages/cli/src/utils/loadIgnorePatterns.test.ts b/packages/cli/src/utils/loadIgnorePatterns.test.ts
new file mode 100644
index 00000000..6cec9d51
--- /dev/null
+++ b/packages/cli/src/utils/loadIgnorePatterns.test.ts
@@ -0,0 +1,226 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import {
+  vi,
+  describe,
+  it,
+  expect,
+  beforeEach,
+  afterEach,
+  Mock,
+  beforeAll,
+} from 'vitest';
+import * as path from 'node:path';
+import { loadGeminiIgnorePatterns } from './loadIgnorePatterns.js';
+import os from 'node:os';
+
+// Define the type for our mock function explicitly.
+type ReadFileSyncMockType = Mock<
+  (path: string, encoding: string) => string | Buffer
+>;
+
+// Declare a variable to hold our mock function instance.
+let mockedFsReadFileSync: ReadFileSyncMockType;
+
+vi.mock('node:fs', async () => {
+  const actualFsModule =
+    await vi.importActual<typeof import('node:fs')>('node:fs');
+  return {
+    ...actualFsModule,
+    readFileSync: vi.fn(), // The factory creates and returns the vi.fn() instance.
+  };
+});
+
+let actualFs: typeof import('node:fs');
+
+describe('loadGeminiIgnorePatterns', () => {
+  let tempDir: string;
+  let consoleLogSpy: Mock<
+    (message?: unknown, ...optionalParams: unknown[]) => void
+  >;
+  let consoleWarnSpy: Mock<
+    (message?: unknown, ...optionalParams: unknown[]) => void
+  >;
+
+  beforeAll(async () => {
+    actualFs = await vi.importActual<typeof import('node:fs')>('node:fs');
+    const mockedFsModule = await import('node:fs');
+    mockedFsReadFileSync =
+      mockedFsModule.readFileSync as unknown as ReadFileSyncMockType;
+  });
+
+  beforeEach(() => {
+    tempDir = actualFs.mkdtempSync(
+      path.join(os.tmpdir(), 'gemini-ignore-test-'),
+    );
+    consoleLogSpy = vi
+      .spyOn(console, 'log')
+      .mockImplementation(() => {}) as Mock<
+      (message?: unknown, ...optionalParams: unknown[]) => void
+    >;
+    consoleWarnSpy = vi
+      .spyOn(console, 'warn')
+      .mockImplementation(() => {}) as Mock<
+      (message?: unknown, ...optionalParams: unknown[]) => void
+    >;
+    mockedFsReadFileSync.mockReset();
+  });
+
+  afterEach(() => {
+    if (actualFs.existsSync(tempDir)) {
+      actualFs.rmSync(tempDir, { recursive: true, force: true });
+    }
+    consoleLogSpy.mockRestore();
+    consoleWarnSpy.mockRestore();
+  });
+
+  it('should load and parse patterns from .geminiignore, ignoring comments and empty lines', () => {
+    const ignoreContent = [
+      '# This is a comment',
+      'pattern1',
+      '  pattern2  ', // Should be trimmed
+      '', // Empty line
+      'pattern3 # Inline comment', // Handled by trim
+      '*.log',
+      '!important.file',
+    ].join('\n');
+    const ignoreFilePath = path.join(tempDir, '.geminiignore');
+    actualFs.writeFileSync(ignoreFilePath, ignoreContent);
+
+    mockedFsReadFileSync.mockImplementation((p: string, encoding: string) => {
+      if (p === ignoreFilePath && encoding === 'utf-8') return ignoreContent;
+      throw new Error(
+        `Mock fs.readFileSync: Unexpected call with path: ${p}, encoding: ${encoding}`,
+      );
+    });
+
+    const patterns = loadGeminiIgnorePatterns(tempDir);
+
+    expect(patterns).toEqual([
+      'pattern1',
+      'pattern2',
+      'pattern3 # Inline comment',
+      '*.log',
+      '!important.file',
+    ]);
+    expect(consoleLogSpy).toHaveBeenCalledWith(
+      expect.stringContaining('Loaded 5 patterns from .geminiignore'),
+    );
+    expect(mockedFsReadFileSync).toHaveBeenCalledWith(ignoreFilePath, 'utf-8');
+  });
+
+  it('should return an empty array and log info if .geminiignore is not found', () => {
+    const ignoreFilePath = path.join(tempDir, '.geminiignore');
+    mockedFsReadFileSync.mockImplementation((p: string, encoding: string) => {
+      if (p === ignoreFilePath && encoding === 'utf-8') {
+        const error = new Error('File not found') as NodeJS.ErrnoException;
+        error.code = 'ENOENT';
+        throw error;
+      }
+      throw new Error(
+        `Mock fs.readFileSync: Unexpected call with path: ${p}, encoding: ${encoding}`,
+      );
+    });
+
+    const patterns = loadGeminiIgnorePatterns(tempDir);
+    expect(patterns).toEqual([]);
+    expect(consoleLogSpy).toHaveBeenCalledWith(
+      '[INFO] No .geminiignore file found. Proceeding without custom ignore patterns.',
+    );
+    expect(mockedFsReadFileSync).toHaveBeenCalledWith(ignoreFilePath, 'utf-8');
+  });
+
+  it('should return an empty array if .geminiignore is empty', () => {
+    const ignoreFilePath = path.join(tempDir, '.geminiignore');
+    actualFs.writeFileSync(ignoreFilePath, '');
+    mockedFsReadFileSync.mockImplementation((p: string, encoding: string) => {
+      if (p === ignoreFilePath && encoding === 'utf-8') return ''; // Return string for empty file
+      throw new Error(
+        `Mock fs.readFileSync: Unexpected call with path: ${p}, encoding: ${encoding}`,
+      );
+    });
+
+    const patterns = loadGeminiIgnorePatterns(tempDir);
+    expect(patterns).toEqual([]);
+    expect(consoleLogSpy).not.toHaveBeenCalledWith(
+      expect.stringContaining('Loaded 0 patterns from .geminiignore'),
+    );
+    expect(consoleLogSpy).not.toHaveBeenCalledWith(
+      expect.stringContaining('No .geminiignore file found'),
+    );
+    expect(mockedFsReadFileSync).toHaveBeenCalledWith(ignoreFilePath, 'utf-8');
+  });
+
+  it('should return an empty array if .geminiignore contains only comments and empty lines', () => {
+    const ignoreContent = [
+      '# Comment 1',
+      '  # Comment 2 with leading spaces',
+      '',
+      '   ', // Whitespace only line
+    ].join('\n');
+    const ignoreFilePath = path.join(tempDir, '.geminiignore');
+    actualFs.writeFileSync(ignoreFilePath, ignoreContent);
+    mockedFsReadFileSync.mockImplementation((p: string, encoding: string) => {
+      if (p === ignoreFilePath && encoding === 'utf-8') return ignoreContent;
+      throw new Error(
+        `Mock fs.readFileSync: Unexpected call with path: ${p}, encoding: ${encoding}`,
+      );
+    });
+
+    const patterns = loadGeminiIgnorePatterns(tempDir);
+    expect(patterns).toEqual([]);
+    expect(consoleLogSpy).not.toHaveBeenCalledWith(
+      expect.stringContaining('Loaded 0 patterns from .geminiignore'),
+    );
+    expect(consoleLogSpy).not.toHaveBeenCalledWith(
+      expect.stringContaining('No .geminiignore file found'),
+    );
+    expect(mockedFsReadFileSync).toHaveBeenCalledWith(ignoreFilePath, 'utf-8');
+  });
+
+  it('should handle read errors (other than ENOENT) and log a warning', () => {
+    const ignoreFilePath = path.join(tempDir, '.geminiignore');
+    mockedFsReadFileSync.mockImplementation((p: string, encoding: string) => {
+      if (p === ignoreFilePath && encoding === 'utf-8') {
+        const error = new Error('Test read error') as NodeJS.ErrnoException;
+        error.code = 'EACCES';
+        throw error;
+      }
+      throw new Error(
+        `Mock fs.readFileSync: Unexpected call with path: ${p}, encoding: ${encoding}`,
+      );
+    });
+
+    const patterns = loadGeminiIgnorePatterns(tempDir);
+    expect(patterns).toEqual([]);
+    expect(consoleWarnSpy).toHaveBeenCalledWith(
+      expect.stringContaining(
+        `[WARN] Could not read .geminiignore file at ${ignoreFilePath}: Test read error`,
+      ),
+    );
+    expect(mockedFsReadFileSync).toHaveBeenCalledWith(ignoreFilePath, 'utf-8');
+  });
+
+  it('should correctly handle patterns with inline comments if not starting with #', () => {
+    const ignoreContent = 'src/important # but not this part';
+    const ignoreFilePath = path.join(tempDir, '.geminiignore');
+    actualFs.writeFileSync(ignoreFilePath, ignoreContent);
+    mockedFsReadFileSync.mockImplementation((p: string, encoding: string) => {
+      if (p === ignoreFilePath && encoding === 'utf-8') return ignoreContent;
+      throw new Error(
+        `Mock fs.readFileSync: Unexpected call with path: ${p}, encoding: ${encoding}`,
+      );
+    });
+
+    const patterns = loadGeminiIgnorePatterns(tempDir);
+    expect(patterns).toEqual(['src/important # but not this part']);
+    expect(consoleLogSpy).toHaveBeenCalledWith(
+      expect.stringContaining('Loaded 1 patterns from .geminiignore'),
+    );
+    expect(mockedFsReadFileSync).toHaveBeenCalledWith(ignoreFilePath, 'utf-8');
+  });
+});
diff --git a/packages/cli/src/utils/loadIgnorePatterns.ts b/packages/cli/src/utils/loadIgnorePatterns.ts
new file mode 100644
index 00000000..3d0a1968
--- /dev/null
+++ b/packages/cli/src/utils/loadIgnorePatterns.ts
@@ -0,0 +1,71 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import * as fs from 'node:fs';
+import * as path from 'node:path';
+
+const GEMINI_IGNORE_FILE_NAME = '.geminiignore';
+
+/**
+ * Loads and parses a .geminiignore file from the given workspace root.
+ * The .geminiignore file follows a format similar to .gitignore:
+ * - Each line specifies a glob pattern.
+ * - Lines are trimmed of leading and trailing whitespace.
+ * - Blank lines (after trimming) are ignored.
+ * - Lines starting with a pound sign (#) (after trimming) are treated as comments and ignored.
+ * - Patterns are case-sensitive and follow standard glob syntax.
+ * - If a # character appears elsewhere in a line (not at the start after trimming),
+ *   it is considered part of the glob pattern.
+ *
+ * @param workspaceRoot The absolute path to the workspace root where the .geminiignore file is expected.
+ * @returns An array of glob patterns extracted from the .geminiignore file. Returns an empty array
+ *          if the file does not exist or contains no valid patterns.
+ */
+export function loadGeminiIgnorePatterns(workspaceRoot: string): string[] {
+  const ignoreFilePath = path.join(workspaceRoot, GEMINI_IGNORE_FILE_NAME);
+  const patterns: string[] = [];
+
+  try {
+    const fileContent = fs.readFileSync(ignoreFilePath, 'utf-8');
+    const lines = fileContent.split(/\r?\n/);
+
+    for (const line of lines) {
+      const trimmedLine = line.trim();
+      if (trimmedLine && !trimmedLine.startsWith('#')) {
+        patterns.push(trimmedLine);
+      }
+    }
+    if (patterns.length > 0) {
+      console.log(
+        `[INFO] Loaded ${patterns.length} patterns from .geminiignore`,
+      );
+    }
+  } catch (error: unknown) {
+    if (
+      error instanceof Error &&
+      'code' in error &&
+      typeof error.code === 'string'
+    ) {
+      if (error.code === 'ENOENT') {
+        // .geminiignore not found, which is fine.
+        console.log(
+          '[INFO] No .geminiignore file found. Proceeding without custom ignore patterns.',
+        );
+      } else {
+        // Other error reading the file (e.g., permissions)
+        console.warn(
+          `[WARN] Could not read .geminiignore file at ${ignoreFilePath}: ${error.message}`,
+        );
+      }
+    } else {
+      // For other types of errors, or if code is not available
+      console.warn(
+        `[WARN] An unexpected error occurred while trying to read ${ignoreFilePath}: ${String(error)}`,
+      );
+    }
+  }
+  return patterns;
+}
diff --git a/packages/core/src/config/config.ts b/packages/core/src/config/config.ts
index deb8b62b..92a929cc 100644
--- a/packages/core/src/config/config.ts
+++ b/packages/core/src/config/config.ts
@@ -70,6 +70,7 @@ export interface ConfigParameters {
   vertexai?: boolean;
   showMemoryUsage?: boolean;
   contextFileName?: string;
+  geminiIgnorePatterns?: string[];
   accessibility?: AccessibilitySettings;
   fileFilteringRespectGitIgnore?: boolean;
   fileFilteringAllowBuildArtifacts?: boolean;
@@ -97,6 +98,7 @@ export class Config {
   private readonly showMemoryUsage: boolean;
   private readonly accessibility: AccessibilitySettings;
   private readonly geminiClient: GeminiClient;
+  private readonly geminiIgnorePatterns: string[] = [];
   private readonly fileFilteringRespectGitIgnore: boolean;
   private readonly fileFilteringAllowBuildArtifacts: boolean;
   private fileDiscoveryService: FileDiscoveryService | null = null;
@@ -129,6 +131,9 @@ export class Config {
     if (params.contextFileName) {
       setGeminiMdFilename(params.contextFileName);
     }
+    if (params.geminiIgnorePatterns) {
+      this.geminiIgnorePatterns = params.geminiIgnorePatterns;
+    }
 
     this.toolRegistry = createToolRegistry(this);
     this.geminiClient = new GeminiClient(this);
@@ -229,6 +234,10 @@ export class Config {
     return this.geminiClient;
   }
 
+  getGeminiIgnorePatterns(): string[] {
+    return this.geminiIgnorePatterns;
+  }
+
   getFileFilteringRespectGitIgnore(): boolean {
     return this.fileFilteringRespectGitIgnore;
   }
@@ -311,7 +320,7 @@ export function createToolRegistry(config: Config): Promise<ToolRegistry> {
   };
 
   registerCoreTool(LSTool, targetDir, config);
-  registerCoreTool(ReadFileTool, targetDir);
+  registerCoreTool(ReadFileTool, targetDir, config);
   registerCoreTool(GrepTool, targetDir);
   registerCoreTool(GlobTool, targetDir, config);
   registerCoreTool(EditTool, config);
diff --git a/packages/core/src/tools/read-file.test.ts b/packages/core/src/tools/read-file.test.ts
index 8ea42134..39c22d06 100644
--- a/packages/core/src/tools/read-file.test.ts
+++ b/packages/core/src/tools/read-file.test.ts
@@ -10,6 +10,7 @@ import * as fileUtils from '../utils/fileUtils.js';
 import path from 'path';
 import os from 'os';
 import fs from 'fs'; // For actual fs operations in setup
+import { Config } from '../config/config.js';
 
 // Mock fileUtils.processSingleFileContent
 vi.mock('../utils/fileUtils', async () => {
@@ -33,7 +34,10 @@ describe('ReadFileTool', () => {
     tempRootDir = fs.mkdtempSync(
       path.join(os.tmpdir(), 'read-file-tool-root-'),
     );
-    tool = new ReadFileTool(tempRootDir);
+    const mockConfigInstance = {
+      getGeminiIgnorePatterns: () => ['**/foo.bar', 'foo.baz', 'foo.*'],
+    } as Config;
+    tool = new ReadFileTool(tempRootDir, mockConfigInstance);
     mockProcessSingleFileContent.mockReset();
   });
 
@@ -224,5 +228,15 @@ describe('ReadFileTool', () => {
         5,
       );
     });
+
+    it('should return error if path is ignored by a .geminiignore pattern', async () => {
+      const params: ReadFileToolParams = {
+        path: path.join(tempRootDir, 'foo.bar'),
+      };
+      const result = await tool.execute(params, abortSignal);
+      expect(result.returnDisplay).toContain('foo.bar');
+      expect(result.returnDisplay).toContain('foo.*');
+      expect(result.returnDisplay).not.toContain('foo.baz');
+    });
   });
 });
diff --git a/packages/core/src/tools/read-file.ts b/packages/core/src/tools/read-file.ts
index f92885ea..5c5994d7 100644
--- a/packages/core/src/tools/read-file.ts
+++ b/packages/core/src/tools/read-file.ts
@@ -5,10 +5,12 @@
  */
 
 import path from 'path';
+import micromatch from 'micromatch';
 import { SchemaValidator } from '../utils/schemaValidator.js';
 import { makeRelative, shortenPath } from '../utils/paths.js';
 import { BaseTool, ToolResult } from './tools.js';
 import { isWithinRoot, processSingleFileContent } from '../utils/fileUtils.js';
+import { Config } from '../config/config.js';
 
 /**
  * Parameters for the ReadFile tool
@@ -35,8 +37,12 @@ export interface ReadFileToolParams {
  */
 export class ReadFileTool extends BaseTool<ReadFileToolParams, ToolResult> {
   static readonly Name: string = 'read_file';
+  private readonly geminiIgnorePatterns: string[];
 
-  constructor(private rootDirectory: string) {
+  constructor(
+    private rootDirectory: string,
+    config: Config,
+  ) {
     super(
       ReadFileTool.Name,
       'ReadFile',
@@ -64,6 +70,7 @@ export class ReadFileTool extends BaseTool<ReadFileToolParams, ToolResult> {
       },
     );
     this.rootDirectory = path.resolve(rootDirectory);
+    this.geminiIgnorePatterns = config.getGeminiIgnorePatterns() || [];
   }
 
   validateToolParams(params: ReadFileToolParams): string | null {
@@ -89,6 +96,19 @@ export class ReadFileTool extends BaseTool<ReadFileToolParams, ToolResult> {
     if (params.limit !== undefined && params.limit <= 0) {
       return 'Limit must be a positive number';
     }
+
+    // Check against .geminiignore patterns
+    if (this.geminiIgnorePatterns.length > 0) {
+      const relativePath = makeRelative(params.path, this.rootDirectory);
+      if (micromatch.isMatch(relativePath, this.geminiIgnorePatterns)) {
+        // Get patterns that matched to show in the error message
+        const matchingPatterns = this.geminiIgnorePatterns.filter((p) =>
+          micromatch.isMatch(relativePath, p),
+        );
+        return `File path '${shortenPath(relativePath)}' is ignored by the following .geminiignore pattern(s):\n\n${matchingPatterns.join('\n')}`;
+      }
+    }
+
     return null;
   }
 
diff --git a/packages/core/src/tools/read-many-files.test.ts b/packages/core/src/tools/read-many-files.test.ts
index f4ecc9d0..eb647c18 100644
--- a/packages/core/src/tools/read-many-files.test.ts
+++ b/packages/core/src/tools/read-many-files.test.ts
@@ -10,10 +10,10 @@ import { describe, it, expect, beforeEach, afterEach } from 'vitest';
 import { mockControl } from '../__mocks__/fs/promises.js';
 import { ReadManyFilesTool } from './read-many-files.js';
 import { FileDiscoveryService } from '../services/fileDiscoveryService.js';
-import { Config } from '../config/config.js';
 import path from 'path';
 import fs from 'fs'; // Actual fs for setup
 import os from 'os';
+import { Config } from '../config/config.js';
 
 describe('ReadManyFilesTool', () => {
   let tool: ReadManyFilesTool;
@@ -31,6 +31,7 @@ describe('ReadManyFilesTool', () => {
     getFileFilteringRespectGitIgnore: () => true,
     getFileFilteringCustomIgnorePatterns: () => [],
     getFileFilteringAllowBuildArtifacts: () => false,
+    getGeminiIgnorePatterns: () => ['**/foo.bar', 'foo.baz', 'foo.*'],
   } as Partial<Config> as Config;
 
   beforeEach(async () => {
@@ -367,5 +368,16 @@ describe('ReadManyFilesTool', () => {
         },
       ]);
     });
+
+    it('should return error if path is ignored by a .geminiignore pattern', async () => {
+      createFile('foo.bar', '');
+      createFile('qux/foo.baz', '');
+      createFile('foo.quux', '');
+      const params = { paths: ['foo.bar', 'qux/foo.baz', 'foo.quux'] };
+      const result = await tool.execute(params, new AbortController().signal);
+      expect(result.returnDisplay).not.toContain('foo.bar');
+      expect(result.returnDisplay).toContain('qux/foo.baz');
+      expect(result.returnDisplay).not.toContain('foo.quux');
+    });
   });
 });
diff --git a/packages/core/src/tools/read-many-files.ts b/packages/core/src/tools/read-many-files.ts
index 30f70c91..718ce510 100644
--- a/packages/core/src/tools/read-many-files.ts
+++ b/packages/core/src/tools/read-many-files.ts
@@ -119,6 +119,7 @@ export class ReadManyFilesTool extends BaseTool<
   ToolResult
 > {
   static readonly Name: string = 'read_many_files';
+  private readonly geminiIgnorePatterns: string[];
 
   /**
    * Creates an instance of ReadManyFilesTool.
@@ -190,6 +191,7 @@ Use this tool when the user's query implies needing the content of several files
       parameterSchema,
     );
     this.targetDir = path.resolve(targetDir);
+    this.geminiIgnorePatterns = config.getGeminiIgnorePatterns() || [];
   }
 
   validateParams(params: ReadManyFilesParams): string | null {
@@ -242,12 +244,26 @@ Use this tool when the user's query implies needing the content of several files
     const allPatterns = [...params.paths, ...(params.include || [])];
     const pathDesc = `using patterns: \`${allPatterns.join('`, `')}\` (within target directory: \`${this.targetDir}\`)`;
 
-    let effectiveExcludes =
-      params.useDefaultExcludes !== false ? [...DEFAULT_EXCLUDES] : [];
-    if (params.exclude && params.exclude.length > 0) {
-      effectiveExcludes = [...effectiveExcludes, ...params.exclude];
+    // Determine the final list of exclusion patterns exactly as in execute method
+    const paramExcludes = params.exclude || [];
+    const paramUseDefaultExcludes = params.useDefaultExcludes !== false;
+
+    const finalExclusionPatternsForDescription: string[] =
+      paramUseDefaultExcludes
+        ? [...DEFAULT_EXCLUDES, ...paramExcludes, ...this.geminiIgnorePatterns]
+        : [...paramExcludes, ...this.geminiIgnorePatterns];
+
+    let excludeDesc = `Excluding: ${finalExclusionPatternsForDescription.length > 0 ? `patterns like \`${finalExclusionPatternsForDescription.slice(0, 2).join('`, `')}${finalExclusionPatternsForDescription.length > 2 ? '...`' : '`'}` : 'none specified'}`;
+
+    // Add a note if .geminiignore patterns contributed to the final list of exclusions
+    if (this.geminiIgnorePatterns.length > 0) {
+      const geminiPatternsInEffect = this.geminiIgnorePatterns.filter((p) =>
+        finalExclusionPatternsForDescription.includes(p),
+      ).length;
+      if (geminiPatternsInEffect > 0) {
+        excludeDesc += ` (includes ${geminiPatternsInEffect} from .geminiignore)`;
+      }
     }
-    const excludeDesc = `Excluding: ${effectiveExcludes.length > 0 ? `patterns like \`${effectiveExcludes.slice(0, 2).join('`, `')}${effectiveExcludes.length > 2 ? '...`' : '`'}` : 'none explicitly (beyond default non-text file avoidance).'}`;
 
     return `Will attempt to read and concatenate files ${pathDesc}. ${excludeDesc}. File encoding: ${DEFAULT_ENCODING}. Separator: "${DEFAULT_OUTPUT_SEPARATOR_FORMAT.replace('{filePath}', 'path/to/file.ext')}".`;
   }
@@ -285,8 +301,8 @@ Use this tool when the user's query implies needing the content of several files
     const contentParts: PartListUnion = [];
 
     const effectiveExcludes = useDefaultExcludes
-      ? [...DEFAULT_EXCLUDES, ...exclude]
-      : [...exclude];
+      ? [...DEFAULT_EXCLUDES, ...exclude, ...this.geminiIgnorePatterns]
+      : [...exclude, ...this.geminiIgnorePatterns];
 
     const searchPatterns = [...inputPatterns, ...include];
     if (searchPatterns.length === 0) {