Gmail MCP

Instructions

Implementation Reference

• src/index.ts:1187-1198 (registration)

  Registration of the 'verify_send_as' MCP tool, including input schema (sendAsEmail string) and inline handler function that uses handleTool to send a verification email to the specified send-as alias via the Gmail API.

  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:1192-1197 (handler)

  The inline handler function for the verify_send_as tool. It invokes the shared handleTool utility with a Gmail API callback to call users.settings.sendAs.verify, which sends the verification email, 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:1189-1191 (schema)

  Input schema for verify_send_as tool using Zod: requires 'sendAsEmail' as a string.

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

• src/index.ts:49-65 (helper)

  Shared helper function used by all tools, including verify_send_as, to create OAuth2 client, validate credentials, set up Gmail client, execute the provided API callback, and handle 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) {
      return `Tool execution failed: ${error.message}`
    }
  }

• src/oauth2.ts:104-124 (helper)

  Helper function called by handleTool to validate and refresh OAuth2 credentials if necessary, ensuring the Gmail API call succeeds.

  export const validateCredentials = async (oauth2Client: OAuth2Client) => {
    try {
      const { credentials } = oauth2Client
      if (!credentials) return false
  
      const expiryDate = credentials.expiry_date
      const needsRefresh = !expiryDate || expiryDate <= Date.now()
  
      if (!needsRefresh) return true
  
      if (!credentials.refresh_token) return false
  
      const { credentials: tokens } = await oauth2Client.refreshAccessToken()
      oauth2Client.setCredentials(tokens)
  
      fs.writeFileSync(GMAIL_CREDENTIALS_PATH, JSON.stringify(tokens, null, 2))
      return true
    } catch (error: any) { 
      return false
    }
  }