Gmail MCP

Instructions

Implementation Reference

• src/index.ts:789-803 (registration)

  Registration of the 'modify_thread' MCP tool, including input schema definition and handler function that calls Gmail API's threads.modify to update labels on a thread.

  server.tool("modify_thread",
    "Modify the labels applied to a thread",
    {
      id: z.string().describe("The ID of the thread to modify"),
      addLabelIds: z.array(z.string()).optional().describe("A list of label IDs to add to the thread"),
      removeLabelIds: z.array(z.string()).optional().describe("A list of label IDs to remove from the thread")
    },
    async (params) => {
      const { id, ...threadData } = params
      return handleTool(config, async (gmail: gmail_v1.Gmail) => {
        const { data } = await gmail.users.threads.modify({ userId: 'me', id, requestBody: threadData })
        return formatResponse(data)
      })
    }
  )

• src/index.ts:796-802 (handler)

  Handler function for 'modify_thread' tool. Extracts thread ID and label changes from params, uses handleTool wrapper to authenticate and call Gmail API's users.threads.modify method.

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

• src/index.ts:792-795 (schema)

  Input schema for 'modify_thread' tool using Zod: requires thread ID, optional arrays for labels to add or remove.

    id: z.string().describe("The ID of the thread to modify"),
    addLabelIds: z.array(z.string()).optional().describe("A list of label IDs to add to the thread"),
    removeLabelIds: z.array(z.string()).optional().describe("A list of label IDs to remove from the thread")
  },

• src/index.ts:50-80 (helper)

  Shared 'handleTool' helper function used by 'modify_thread' and other tools for OAuth 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)

  Utility function 'formatResponse' used to standardize tool responses as MCP content blocks with JSON-stringified data.

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