Gmail MCP Server

Instructions

Implementation Reference

• src/index.ts:575-591 (handler)

  Full handler implementation for the 'get_message' MCP tool: registers the tool, defines input schema, fetches Gmail message by ID, processes payload (decodes body, filters headers), handles auth/errors via handleTool, and formats response.
  server.tool("get_message", "Get a specific message by ID with format options", { id: z.string().describe("The ID of the message to retrieve"), 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.get({ userId: 'me', id: params.id, format: 'full' }) if (data.payload) { data.payload = processMessagePart(data.payload, params.includeBodyHtml) } return formatResponse(data) }) }
• src/index.ts:577-580 (schema)

  Zod input schema for the get_message tool: requires message ID, optional flag to include HTML bodies.
  { id: z.string().describe("The ID of the message to retrieve"), 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 tools, including get_message: creates/validates OAuth2 client, executes Gmail API call, 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}` }); } }
• src/index.ts:94-108 (helper)

  Helper to process message payload for get_message: recursively decodes base64 bodies (unless HTML and not requested), filters headers to essentials.
  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:82-92 (helper)

  Utility helper called by processMessagePart: decodes base64url-encoded message body data to UTF-8 text.
  const decodedBody = (body: MessagePartBody) => { if (!body?.data) return body const decodedData = Buffer.from(body.data, 'base64').toString('utf-8') const decodedBody: MessagePartBody = { data: decodedData, size: body.data.length, attachmentId: body.attachmentId } return decodedBody }