Gmail MCP Server

Instructions

Implementation Reference

• src/index.ts:763-787 (handler)

  Handler function for the 'list_threads' MCP tool. Authenticates via handleTool, calls Gmail API users.threads.list with params, processes each thread's messages by applying processMessagePart to payloads (decoding bodies, filtering headers), and formats the response.
  async (params) => { return handleTool(config, async (gmail: gmail_v1.Gmail) => { const { data } = await gmail.users.threads.list({ userId: 'me', ...params }) if (data.threads) { data.threads = data.threads.map(thread => { if (thread.messages) { thread.messages = thread.messages.map(message => { if (message.payload) { message.payload = processMessagePart( message.payload, params.includeBodyHtml ) } return message }) } return thread }) } return formatResponse(data) }) } )
• src/index.ts:756-762 (schema)

  Zod input schema defining parameters for the list_threads tool: maxResults, pageToken, q (search query), labelIds, includeSpamTrash, includeBodyHtml.
  maxResults: z.number().optional().describe("Maximum number of threads to return"), pageToken: z.string().optional().describe("Page token to retrieve a specific page of results"), q: z.string().optional().describe("Only return threads matching the specified query"), labelIds: z.array(z.string()).optional().describe("Only return threads with labels that match all of the specified label IDs"), includeSpamTrash: z.boolean().optional().describe("Include threads from SPAM and TRASH in the results"), includeBodyHtml: z.boolean().optional().describe("Whether to include the parsed HTML in the return for each body, excluded by default because they can be excessively large"), },
• src/index.ts:753-755 (registration)

  Registration of the 'list_threads' tool on the McpServer instance, specifying name, description, input schema, and handler function.
  server.tool("list_threads", "List threads in the user's mailbox", {
• src/index.ts:94-108 (helper)

  Helper function to process Gmail message parts: decodes base64 data to UTF-8 for non-HTML or specified HTML bodies, recursively processes parts, filters headers to a predefined list.
  const processMessagePart = (messagePart: MessagePart, includeBodyHtml = false): MessagePart => { if ((messagePart.mimeType !== 'text/html' || includeBodyHtml) && messagePart.body) { messagePart.body = decodedBody(messagePart.body) } if (messagePart.parts) { messagePart.parts = messagePart.parts.map(part => processMessagePart(part, includeBodyHtml)) } if (messagePart.headers) { messagePart.headers = messagePart.headers.filter(header => RESPONSE_HEADERS_LIST.includes(header.name || '')) } return messagePart }
• src/index.ts:50-80 (helper)

  Shared helper for all Gmail tools: creates/validates OAuth2 client, initializes Gmail client, executes the provided API callback, handles auth errors specifically.
  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) { // Check for specific authentication errors if ( error.message?.includes("invalid_grant") || error.message?.includes("refresh_token") || error.message?.includes("invalid_client") || error.message?.includes("unauthorized_client") || error.code === 401 || error.code === 403 ) { return formatResponse({ error: `Authentication failed: ${error.message}. Please re-authenticate by running: npx @shinzolabs/gmail-mcp auth`, }); } return formatResponse({ error: `Tool execution failed: ${error.message}` }); } }