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/chat/agent.ts

@@ -271,7 +271,7 @@ const createPrompt = ({
         The user has explicitly selected the following repositories for analysis:
         ${repos.map(repo => `- ${repo}`).join('\n')}
 
-        When calling tools that accept a \`repo\` parameter (e.g. \`read_file\`, \`list_commits\`, \`list_tree\`, \`grep\`), use these repository names exactly as listed above, including the full host prefix (e.g. \`github.com/org/repo\`).
+        When calling tools that accept a \`repo\` parameter (e.g. \`read_file\`, \`list_commits\`, \`list_tree\`, \`get_diff\`, \`grep\`), use these repository names exactly as listed above, including the full host prefix (e.g. \`github.com/org/repo\`).
 
         When using \`grep\` to search across ALL selected repositories (e.g. "which repos have X?"), omit the \`repo\` parameter entirely — the tool will automatically search across all selected repositories in a single call. Do NOT call \`grep\` once per repository when a single broad search would suffice.
         </selected_repositories>

packages/web/src/features/chat/components/chatThread/detailsCard.tsx

@@ -19,6 +19,7 @@ import { FindSymbolDefinitionsToolComponent } from './tools/findSymbolDefinition
 import { FindSymbolReferencesToolComponent } from './tools/findSymbolReferencesToolComponent';
 import { GlobToolComponent } from './tools/globToolComponent';
 import { GrepToolComponent } from './tools/grepToolComponent';
+import { GetDiffToolComponent } from './tools/getDiffToolComponent';
 import { ListCommitsToolComponent } from './tools/listCommitsToolComponent';
 import { ListReposToolComponent } from './tools/listReposToolComponent';
 import { ListTreeToolComponent } from './tools/listTreeToolComponent';
@@ -289,6 +290,15 @@ export const StepPartRenderer = ({ part }: { part: SBChatMessagePart }) => {
                     {(output) => <ListCommitsToolComponent {...output} />}
                 </ToolOutputGuard>
             )
+        case 'tool-get_diff':
+            return (
+                <ToolOutputGuard
+                    part={part}
+                    loadingText="Comparing revisions..."
+                >
+                    {(output) => <GetDiffToolComponent {...output} />}
+                </ToolOutputGuard>
+            )
         case 'tool-list_tree':
             return (
                 <ToolOutputGuard

packages/web/src/features/chat/components/chatThread/tools/getDiffToolComponent.tsx

@@ -0,0 +1,30 @@
+'use client';
+
+import { Separator } from '@/components/ui/separator';
+import { GetDiffMetadata, ToolResult } from '@/features/tools';
+
+export const GetDiffToolComponent = ({ metadata }: ToolResult<GetDiffMetadata>) => {
+    const fileCount = metadata.files.length;
+
+    return (
+        <div className="flex items-center gap-2 select-none cursor-default text-sm text-muted-foreground">
+            <span className="flex-shrink-0">Compared</span>
+            <span className="text-xs font-mono bg-muted px-1.5 py-0.5 rounded text-foreground">
+                {metadata.base}
+            </span>
+            <span className="flex-shrink-0">to</span>
+            <span className="text-xs font-mono bg-muted px-1.5 py-0.5 rounded text-foreground">
+                {metadata.head}
+            </span>
+            <span className="flex-shrink-0">in</span>
+            <span className="text-xs font-mono bg-muted px-1.5 py-0.5 rounded text-foreground truncate">
+                {metadata.repo}
+            </span>
+            <span className="flex-1" />
+            <span className="text-xs flex-shrink-0">
+                {fileCount} changed {fileCount === 1 ? 'file' : 'files'}
+            </span>
+            <Separator orientation="vertical" className="h-3 flex-shrink-0" />
+        </div>
+    );
+};

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

@@ -3,6 +3,7 @@ import {
     readFileDefinition,
     listCommitsDefinition,
     listReposDefinition,
+    getDiffDefinition,
     grepDefinition,
     globDefinition,
     findSymbolReferencesDefinition,
@@ -17,6 +18,7 @@ export const createTools = (context: ToolContext) => ({
     [readFileDefinition.name]: toVercelAITool(readFileDefinition, context),
     [listCommitsDefinition.name]: toVercelAITool(listCommitsDefinition, context),
     [listReposDefinition.name]: toVercelAITool(listReposDefinition, context),
+    [getDiffDefinition.name]: toVercelAITool(getDiffDefinition, context),
     [grepDefinition.name]: toVercelAITool(grepDefinition, context),
     [globDefinition.name]: toVercelAITool(globDefinition, context),
     [findSymbolReferencesDefinition.name]: toVercelAITool(findSymbolReferencesDefinition, context),
@@ -27,6 +29,7 @@ export const createTools = (context: ToolContext) => ({
 export type ReadFileToolUIPart = ToolUIPart<{ read_file: SBChatMessageToolTypes['read_file'] }>;
 export type ListCommitsToolUIPart = ToolUIPart<{ list_commits: SBChatMessageToolTypes['list_commits'] }>;
 export type ListReposToolUIPart = ToolUIPart<{ list_repos: SBChatMessageToolTypes['list_repos'] }>;
+export type GetDiffToolUIPart = ToolUIPart<{ get_diff: SBChatMessageToolTypes['get_diff'] }>;
 export type GrepToolUIPart = ToolUIPart<{ grep: SBChatMessageToolTypes['grep'] }>;
 export type GlobToolUIPart = ToolUIPart<{ glob: SBChatMessageToolTypes['glob'] }>;
 export type FindSymbolReferencesToolUIPart = ToolUIPart<{ find_symbol_references: SBChatMessageToolTypes['find_symbol_references'] }>;

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';