Gmail MCP Server

Instructions

Implementation Reference

• src/index.ts:853-862 (registration)

  Registration of the 'get_language' MCP tool. Includes empty input schema and inline handler function that uses shared 'handleTool' to call Gmail API's users.settings.getLanguage and format the response.
  server.tool("get_language", "Gets language settings", {}, async () => { return handleTool(config, async (gmail: gmail_v1.Gmail) => { const { data } = await gmail.users.settings.getLanguage({ userId: 'me' }) return formatResponse(data) }) } )
• src/index.ts:856-861 (handler)

  Inline handler for 'get_language' tool. Executes the core logic by calling Gmail API via handleTool to retrieve user's language settings.
  async () => { return handleTool(config, async (gmail: gmail_v1.Gmail) => { const { data } = await gmail.users.settings.getLanguage({ userId: 'me' }) return formatResponse(data) }) }
• src/index.ts:50-80 (helper)

  Shared helper function 'handleTool' used by all tools, including 'get_language', to handle OAuth2 authentication, create Gmail client, execute the API call, and manage 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:48-49 (helper)

  Helper function 'formatResponse' used to standardize tool responses as MCP content blocks with JSON stringified data.
  const formatResponse = (response: any) => ({ content: [{ type: "text", text: JSON.stringify(response) }] })
• src/index.ts:855-855 (schema)

  Input schema for 'get_language' tool: empty object indicating no input parameters required.
  {},