Gmail MCP

Instructions

Implementation Reference

• src/index.ts:1276-1287 (registration)

  Registration of the list_smime_info MCP tool, defining its input schema, description, and inline handler function that uses the Gmail API to list S/MIME configurations for a given send-as email address.

  server.tool("list_smime_info",
    "Lists S/MIME configs for the specified send-as alias",
    {
      sendAsEmail: z.string().describe("The email address that appears in the 'From:' header")
    },
    async (params) => {
      return handleTool(config, async (gmail: gmail_v1.Gmail) => {
        const { data } = await gmail.users.settings.sendAs.smimeInfo.list({ userId: 'me', sendAsEmail: params.sendAsEmail })
        return formatResponse(data)
      })
    }
  )

• src/index.ts:1281-1286 (handler)

  Handler function for list_smime_info tool, which authenticates via handleTool, calls Gmail API to list S/MIME info for the specified sendAsEmail, and formats the response.

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

• src/index.ts:1278-1280 (schema)

  Input schema for list_smime_info tool using Zod: requires sendAsEmail string.

  {
    sendAsEmail: z.string().describe("The email address that appears in the 'From:' header")
  },

• src/index.ts:50-80 (helper)

  Shared helper function handleTool used by list_smime_info (and other tools) to handle OAuth2 authentication, Gmail client creation, API call execution, and error handling.

  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 for list_smime_info (and other tools).

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