Gmail MCP Server

Instructions

Implementation Reference

• src/index.ts:1314-1327 (registration)

  Registration of the 'watch_mailbox' tool, including description, input schema, and inline handler function that uses the Gmail API to watch the mailbox for changes.

  server.tool("watch_mailbox",
    "Watch for changes to the user's mailbox",
    {
      topicName: z.string().describe("The name of the Cloud Pub/Sub topic to publish notifications to"),
      labelIds: z.array(z.string()).optional().describe("Label IDs to restrict notifications to"),
      labelFilterAction: z.enum(['include', 'exclude']).optional().describe("Whether to include or exclude the specified labels")
    },
    async (params) => {
      return handleTool(config, async (gmail: gmail_v1.Gmail) => {
        const { data } = await gmail.users.watch({ userId: 'me', requestBody: params })
        return formatResponse(data)
      })
    }
  )

• src/index.ts:1321-1326 (handler)

  The handler function for the watch_mailbox tool. It invokes handleTool which authenticates and calls the Gmail API's users.watch method to set up push notifications for mailbox changes.

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

• src/index.ts:1316-1320 (schema)

  Zod input schema for the watch_mailbox tool, defining parameters: topicName (required string), labelIds (optional array of strings), labelFilterAction (optional enum: 'include' or 'exclude').

  {
    topicName: z.string().describe("The name of the Cloud Pub/Sub topic to publish notifications to"),
    labelIds: z.array(z.string()).optional().describe("Label IDs to restrict notifications to"),
    labelFilterAction: z.enum(['include', 'exclude']).optional().describe("Whether to include or exclude the specified labels")
  },

• src/index.ts:50-80 (helper)

  Shared helper function used by all tools, including watch_mailbox, to handle OAuth2 authentication, create Gmail client, execute the API call, and format 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}` });
    }
  }