Gmail MCP

Instructions

Implementation Reference

• src/index.ts:1127-1143 (registration)

  Registration of the 'create_send_as' MCP tool, including inline schema definition and handler function that creates a custom send-as alias using the Gmail API.

  server.tool("create_send_as",
    "Creates a custom send-as alias",
    {
      sendAsEmail: z.string().describe("The email address that appears in the 'From:' header"),
      displayName: z.string().optional().describe("A name that appears in the 'From:' header"),
      replyToAddress: z.string().optional().describe("An optional email address that is included in a 'Reply-To:' header"),
      signature: z.string().optional().describe("An optional HTML signature"),
      isPrimary: z.boolean().optional().describe("Whether this address is the primary address"),
      treatAsAlias: z.boolean().optional().describe("Whether Gmail should treat this address as an alias")
    },
    async (params) => {
      return handleTool(config, async (gmail: gmail_v1.Gmail) => {
        const { data } = await gmail.users.settings.sendAs.create({ userId: 'me', requestBody: params })
        return formatResponse(data)
      })
    }
  )

• src/index.ts:1137-1142 (handler)

  Handler function for 'create_send_as' tool. Uses handleTool wrapper to authenticate, then calls Gmail API to create a send-as alias with the provided parameters.

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

• src/index.ts:1129-1136 (schema)

  Zod schema defining the input parameters for the 'create_send_as' tool, including sendAsEmail (required), and optional fields like displayName, replyToAddress, signature, isPrimary, treatAsAlias.

  {
    sendAsEmail: z.string().describe("The email address that appears in the 'From:' header"),
    displayName: z.string().optional().describe("A name that appears in the 'From:' header"),
    replyToAddress: z.string().optional().describe("An optional email address that is included in a 'Reply-To:' header"),
    signature: z.string().optional().describe("An optional HTML signature"),
    isPrimary: z.boolean().optional().describe("Whether this address is the primary address"),
    treatAsAlias: z.boolean().optional().describe("Whether Gmail should treat this address as an alias")
  },

• src/index.ts:50-80 (helper)

  Shared helper function 'handleTool' used by 'create_send_as' and other tools to handle OAuth2 authentication, credential validation, Gmail client creation, API call execution, and error handling (especially 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:48-49 (helper)

  Helper function 'formatResponse' used to standardize tool responses by wrapping them in MCP content format with JSON stringified data.

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