Gmail MCP Server

Instructions

Implementation Reference

• src/index.ts:594-623 (registration)

  Registration of the list_messages tool using McpServer.tool(), including description, input schema validation with Zod, and the execution handler function.
  server.tool("list_messages", "List messages in the user's mailbox with optional filtering", { maxResults: z.number().optional().describe("Maximum number of messages to return. Accepts values between 1-500"), pageToken: z.string().optional().describe("Page token to retrieve a specific page of results"), q: z.string().optional().describe("Only return messages matching the specified query. Supports the same query format as the Gmail search box"), labelIds: z.array(z.string()).optional().describe("Only return messages with labels that match all of the specified label IDs"), includeSpamTrash: z.boolean().optional().describe("Include messages 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"), }, async (params) => { return handleTool(config, async (gmail: gmail_v1.Gmail) => { const { data } = await gmail.users.messages.list({ userId: 'me', ...params }) if (data.messages) { data.messages = data.messages.map((message: Message) => { if (message.payload) { message.payload = processMessagePart( message.payload, params.includeBodyHtml ) } return message }) } return formatResponse(data) }) } )
• src/index.ts:604-622 (handler)

  The handler function that executes the list_messages tool logic: invokes Gmail API to list messages with user-provided params, processes each message payload (decoding bodies, filtering headers), and formats the response.
  async (params) => { return handleTool(config, async (gmail: gmail_v1.Gmail) => { const { data } = await gmail.users.messages.list({ userId: 'me', ...params }) if (data.messages) { data.messages = data.messages.map((message: Message) => { if (message.payload) { message.payload = processMessagePart( message.payload, params.includeBodyHtml ) } return message }) } return formatResponse(data) }) }
• src/index.ts:597-603 (schema)

  Input schema using Zod for validating parameters to the list_messages tool.
  maxResults: z.number().optional().describe("Maximum number of messages to return. Accepts values between 1-500"), pageToken: z.string().optional().describe("Page token to retrieve a specific page of results"), q: z.string().optional().describe("Only return messages matching the specified query. Supports the same query format as the Gmail search box"), labelIds: z.array(z.string()).optional().describe("Only return messages with labels that match all of the specified label IDs"), includeSpamTrash: z.boolean().optional().describe("Include messages 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:50-80 (helper)

  Shared helper function used by all Gmail tools: creates/validates OAuth2 client, initializes Gmail client, executes the provided API callback, handles authentication and general errors.
  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}` }); } }
• src/index.ts:94-108 (helper)

  Recursive helper to process Gmail message parts: base64-decodes text bodies (skips HTML unless flagged), recurses on nested parts, filters headers to essential ones (Date, From, To, etc.).
  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 }