Gmail MCP

Instructions

Implementation Reference

• src/index.ts:853-862 (registration)

  Registration of the 'get_language' MCP tool, including empty input schema and inline asynchronous handler function that retrieves Gmail language settings via the Gmail API.

  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:856-862 (handler)

  Handler function for 'get_language' tool: calls handleTool with Gmail client to execute gmail.users.settings.getLanguage API and formats response.

    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 get_language (and other tools) to handle OAuth2 authentication, Gmail client creation, API call execution, and error handling including auth-specific responses.

  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)

  Shared helper formatResponse used by get_language (and other tools) to format API results into MCP content structure.

  const formatResponse = (response: any) => ({ content: [{ type: "text", text: JSON.stringify(response) }] })