Gmail MCP

Instructions

Implementation Reference

• src/index.ts:317-330 (handler)

  The handler function for the 'get_draft' tool. It retrieves a specific Gmail draft by ID using the Gmail API with format 'full', processes the message payload (decoding bodies if applicable and filtering headers), and returns a formatted response.

  async (params) => {
    return handleTool(config, async (gmail: gmail_v1.Gmail) => {
      const { data } = await gmail.users.drafts.get({ userId: 'me', id: params.id, format: 'full' })
  
      if (data.message?.payload) {
        data.message.payload = processMessagePart(
          data.message.payload,
          params.includeBodyHtml
        )
      }
  
      return formatResponse(data)
    })
  }

• src/index.ts:313-316 (schema)

  Zod input schema for the 'get_draft' tool defining parameters: required 'id' (draft ID) and optional 'includeBodyHtml' boolean.

  {
    id: z.string().describe("The ID of the draft to retrieve"),
    includeBodyHtml: z.boolean().optional().describe("Whether to include the parsed HTML in the return for each body, excluded by default because they can be excessively large")
  },

• src/index.ts:311-331 (registration)

  Registration of the 'get_draft' tool on the MCP server, including name, description, input schema, and handler reference.

  server.tool("get_draft",
    "Get a specific draft by ID",
    {
      id: z.string().describe("The ID of the draft to retrieve"),
      includeBodyHtml: z.boolean().optional().describe("Whether to include the parsed HTML in the return for each body, excluded by default because they can be excessively large")
    },
    async (params) => {
      return handleTool(config, async (gmail: gmail_v1.Gmail) => {
        const { data } = await gmail.users.drafts.get({ userId: 'me', id: params.id, format: 'full' })
  
        if (data.message?.payload) {
          data.message.payload = processMessagePart(
            data.message.payload,
            params.includeBodyHtml
          )
        }
  
        return formatResponse(data)
      })
    }
  )

• src/index.ts:50-80 (helper)

  Shared helper function used by all Gmail tools, including get_draft, to handle OAuth2 client creation, credential validation, Gmail client instantiation, API call execution, and error handling with specific auth error messages.

  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:94-108 (helper)

  Recursive helper function to process message parts: decodes base64 bodies for non-HTML or opted-in HTML parts, recursively processes child parts, and filters headers to a predefined list. Used in get_draft to prepare the response payload.

  const processMessagePart = (messagePart: MessagePart, includeBodyHtml = false): MessagePart => {
    if ((messagePart.mimeType !== 'text/html' || includeBodyHtml) && messagePart.body) {
      messagePart.body = decodedBody(messagePart.body)
    }
  
    if (messagePart.parts) {
      messagePart.parts = messagePart.parts.map(part => processMessagePart(part, includeBodyHtml))
    }
  
    if (messagePart.headers) {
      messagePart.headers = messagePart.headers.filter(header => RESPONSE_HEADERS_LIST.includes(header.name || ''))
    }
  
    return messagePart
  }