Gmail MCP Server

Instructions

Implementation Reference

• src/index.ts:916-927 (registration)

  Registration of the 'update_language' MCP tool, including input schema (displayLanguage: string) and inline handler that calls Gmail API via handleTool
  server.tool("update_language", "Updates language settings", { displayLanguage: z.string().describe("The language to display Gmail in, formatted as an RFC 3066 Language Tag") }, async (params) => { return handleTool(config, async (gmail: gmail_v1.Gmail) => { const { data } = await gmail.users.settings.updateLanguage({ userId: 'me', requestBody: params }) return formatResponse(data) }) } )
• src/index.ts:921-926 (handler)

  Handler function for 'update_language' tool that invokes handleTool with the Gmail API call to updateLanguage
  async (params) => { return handleTool(config, async (gmail: gmail_v1.Gmail) => { const { data } = await gmail.users.settings.updateLanguage({ userId: 'me', requestBody: params }) return formatResponse(data) }) }
• src/index.ts:918-920 (schema)

  Input schema for 'update_language' tool using Zod: displayLanguage as string with description
  { displayLanguage: z.string().describe("The language to display Gmail in, formatted as an RFC 3066 Language Tag") },
• src/index.ts:50-80 (helper)

  Shared helper function handleTool that manages OAuth2 client creation, validation, Gmail API client setup, executes the provided apiCall, and handles errors including auth failures
  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:48-48 (helper)

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