Gmail MCP Server

Instructions

Implementation Reference

• src/index.ts:1220-1231 (registration)

  Registers the 'verify_send_as' MCP tool with input schema (sendAsEmail: string) and inline handler that uses the Gmail API to send a verification email to the specified send-as alias via gmail.users.settings.sendAs.verify, wrapped in handleTool for auth and error handling.

  server.tool("verify_send_as",
    "Sends a verification email to the specified send-as alias",
    {
      sendAsEmail: z.string().describe("The send-as alias to be verified")
    },
    async (params) => {
      return handleTool(config, async (gmail: gmail_v1.Gmail) => {
        const { data } = await gmail.users.settings.sendAs.verify({ userId: 'me', sendAsEmail: params.sendAsEmail })
        return formatResponse(data)
      })
    }
  )

• src/index.ts:1225-1230 (handler)

  The handler function for the 'verify_send_as' tool, which authenticates via handleTool, calls the Gmail API's verify method on sendAs, and formats the response.

  async (params) => {
    return handleTool(config, async (gmail: gmail_v1.Gmail) => {
      const { data } = await gmail.users.settings.sendAs.verify({ userId: 'me', sendAsEmail: params.sendAsEmail })
      return formatResponse(data)
    })
  }

• src/index.ts:1222-1224 (schema)

  Zod schema defining the input parameter for the 'verify_send_as' tool: sendAsEmail (string).

  {
    sendAsEmail: z.string().describe("The send-as alias to be verified")
  },

• src/index.ts:50-80 (helper)

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

  Helper to format tool responses as MCP content blocks with JSON stringified data.

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