feat(web): expose get_diff on MCP server

Add a new get_diff MCP tool backed by the existing git diff API so agents can request structured diffs between refs. Document the tool in MCP docs with parameters aligned to the public API spec.

Made-with: Cursor

Author: msukkari

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';