Gmail MCP Server

Instructions

Implementation Reference

• src/index.ts:775-789 (registration)

  Registration of the 'modify_thread' tool, including inline schema definition and handler function that modifies thread labels via Gmail API using threads.modify
  server.tool("modify_thread", "Modify the labels applied to a thread", { id: z.string().describe("The ID of the thread to modify"), addLabelIds: z.array(z.string()).optional().describe("A list of label IDs to add to the thread"), removeLabelIds: z.array(z.string()).optional().describe("A list of label IDs to remove from the thread") }, async (params) => { const { id, ...threadData } = params return handleTool(config, async (gmail: gmail_v1.Gmail) => { const { data } = await gmail.users.threads.modify({ userId: 'me', id, requestBody: threadData }) return formatResponse(data) }) } )
• src/index.ts:782-788 (handler)

  Handler executes tool logic: destructures thread ID, calls handleTool to invoke Gmail users.threads.modify with add/remove label IDs, formats response
  async (params) => { const { id, ...threadData } = params return handleTool(config, async (gmail: gmail_v1.Gmail) => { const { data } = await gmail.users.threads.modify({ userId: 'me', id, requestBody: threadData }) return formatResponse(data) }) }
• src/index.ts:777-781 (schema)

  Zod schema for input parameters: required thread ID, optional arrays of label IDs to add/remove
  { id: z.string().describe("The ID of the thread to modify"), addLabelIds: z.array(z.string()).optional().describe("A list of label IDs to add to the thread"), removeLabelIds: z.array(z.string()).optional().describe("A list of label IDs to remove from the thread") },
• src/index.ts:50-66 (helper)

  Shared helper function handleTool that sets up OAuth2/Gmail client and executes the API call provided
  const handleTool = async (queryConfig: Record<string, any> | undefined, apiCall: (gmail: gmail_v1.Gmail) => Promise<any>) => { try { const oauth2Client = queryConfig ? createOAuth2Client(queryConfig) : defaultOAuth2Client if (!oauth2Client) throw new Error('OAuth2 client could not be created, please check your credentials') const credentialsAreValid = await validateCredentials(oauth2Client) if (!credentialsAreValid) throw new Error('OAuth2 credentials are invalid, please re-authenticate') const gmailClient = queryConfig ? google.gmail({ version: 'v1', auth: oauth2Client }) : defaultGmailClient if (!gmailClient) throw new Error('Gmail client could not be created, please check your credentials') const result = await apiCall(gmailClient) return result } catch (error: any) { return `Tool execution failed: ${error.message}` } }
• src/index.ts:48-48 (helper)

  Helper to format API responses as MCP content blocks with JSON stringified data
  const formatResponse = (response: any) => ({ content: [{ type: "text", text: JSON.stringify(response) }] })