feat(web): expose get_diff on MCP server

CHANGELOG.md

@@ -7,6 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+- Added a `get_diff` MCP tool to return structured diffs between two git refs. [#1142](https://github.com/sourcebot-dev/sourcebot/pull/1142)
+
 ### Changed
 - Synced `vendor/zoekt` with upstream `sourcegraph/zoekt`. [#1140](https://github.com/sourcebot-dev/sourcebot/pull/1140)
 

docs/docs/features/mcp-server.mdx

@@ -388,6 +388,17 @@ Parameters:
 | `ref` | no | Commit SHA, branch or tag name to search on. If not provided, defaults to the default branch. |
 | `limit` | no | Maximum number of files to return (default: 100). |
 
+### `get_diff`
+
+Returns a structured diff between two refs in a repository using a two-dot comparison.
+
+Parameters:
+| Name | Required | Description |
+|:----------|:---------|:--------------------------------------------------------------------------------------------------------------|
+| `repo` | yes | The fully-qualified repository name. |
+| `base` | yes | The base git ref (branch, tag, or commit SHA) to diff from. |
+| `head` | yes | The head git ref (branch, tag, or commit SHA) to diff to. |
+
 ### `find_symbol_definitions`
 
 Finds where a symbol (function, class, variable, etc.) is defined in a repository.

packages/web/src/features/mcp/server.ts

@@ -13,6 +13,7 @@ import { getConfiguredLanguageModelsInfo } from "../chat/utils.server";
 import {
     findSymbolDefinitionsDefinition,
     findSymbolReferencesDefinition,
+    getDiffDefinition,
     listCommitsDefinition,
     listReposDefinition,
     listTreeDefinition,
@@ -40,6 +41,7 @@ export async function createMcpServer(): Promise<McpServer> {
 
     registerMcpTool(server, grepDefinition, toolContext);
     registerMcpTool(server, globDefinition, toolContext);
+    registerMcpTool(server, getDiffDefinition, toolContext);
     registerMcpTool(server, listCommitsDefinition, toolContext);
     registerMcpTool(server, listReposDefinition, toolContext);
     registerMcpTool(server, readFileDefinition, toolContext);

packages/web/src/features/tools/getDiff.ts

@@ -0,0 +1,40 @@
+import { getDiff, GetDiffResult } from '@/features/git';
+import { getDiffRequestSchema } from '@/features/git/schemas';
+import { isServiceError } from '@/lib/utils';
+import description from './getDiff.txt';
+import { logger } from './logger';
+import { ToolDefinition } from './types';
+
+export type GetDiffMetadata = GetDiffResult & {
+    repo: string;
+    base: string;
+    head: string;
+};
+
+export const getDiffDefinition: ToolDefinition<'get_diff', typeof getDiffRequestSchema.shape, GetDiffMetadata> = {
+    name: 'get_diff',
+    title: 'Get diff',
+    isReadOnly: true,
+    isIdempotent: true,
+    description,
+    inputSchema: getDiffRequestSchema,
+    execute: async ({ repo, base, head }, _context) => {
+        logger.debug('get_diff', { repo, base, head });
+
+        const response = await getDiff({ repo, base, head });
+
+        if (isServiceError(response)) {
+            throw new Error(response.message);
+        }
+
+        return {
+            output: JSON.stringify(response),
+            metadata: {
+                ...response,
+                repo,
+                base,
+                head,
+            },
+        };
+    },
+};

packages/web/src/features/tools/getDiff.txt

@@ -0,0 +1,4 @@
+Returns a structured git diff between two refs in a repository.
+
+Use this tool when you need patch details (added, removed, and context lines) between a base and head revision.
+The output includes changed files and hunks with line ranges and diff body content.

packages/web/src/features/tools/index.ts

@@ -3,6 +3,7 @@ export * from './listCommits';
 export * from './listRepos';
 export * from './grep';
 export * from './glob';
+export * from './getDiff';
 export * from './findSymbolReferences';
 export * from './findSymbolDefinitions';
 export * from './listTree';