list_messages

Instructions

Implementation Reference

• src/index.ts:594-623 (registration)

  Registration of the list_messages tool using McpServer.tool(), including description, input schema validation with Zod, and the execution handler function.

  server.tool("list_messages",
    "List messages in the user's mailbox with optional filtering",
    {
      maxResults: z.number().optional().describe("Maximum number of messages to return. Accepts values between 1-500"),
      pageToken: z.string().optional().describe("Page token to retrieve a specific page of results"),
      q: z.string().optional().describe("Only return messages matching the specified query. Supports the same query format as the Gmail search box"),
      labelIds: z.array(z.string()).optional().describe("Only return messages with labels that match all of the specified label IDs"),
      includeSpamTrash: z.boolean().optional().describe("Include messages from SPAM and TRASH in the results"),
      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.messages.list({ userId: 'me', ...params })
  
        if (data.messages) {
          data.messages = data.messages.map((message: Message) => {
            if (message.payload) {
              message.payload = processMessagePart(
                message.payload,
                params.includeBodyHtml
              )
            }
            return message
          })
        }
  
        return formatResponse(data)
      })
    }
  )

• src/index.ts:604-622 (handler)

  The handler function that executes the list_messages tool logic: invokes Gmail API to list messages with user-provided params, processes each message payload (decoding bodies, filtering headers), and formats the response.

  async (params) => {
    return handleTool(config, async (gmail: gmail_v1.Gmail) => {
      const { data } = await gmail.users.messages.list({ userId: 'me', ...params })
  
      if (data.messages) {
        data.messages = data.messages.map((message: Message) => {
          if (message.payload) {
            message.payload = processMessagePart(
              message.payload,
              params.includeBodyHtml
            )
          }
          return message
        })
      }
  
      return formatResponse(data)
    })
  }

• src/index.ts:597-603 (schema)

  Input schema using Zod for validating parameters to the list_messages tool.

    maxResults: z.number().optional().describe("Maximum number of messages to return. Accepts values between 1-500"),
    pageToken: z.string().optional().describe("Page token to retrieve a specific page of results"),
    q: z.string().optional().describe("Only return messages matching the specified query. Supports the same query format as the Gmail search box"),
    labelIds: z.array(z.string()).optional().describe("Only return messages with labels that match all of the specified label IDs"),
    includeSpamTrash: z.boolean().optional().describe("Include messages from SPAM and TRASH in the results"),
    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:50-80 (helper)

  Shared helper function used by all Gmail tools: creates/validates OAuth2 client, initializes Gmail client, executes the provided API callback, handles authentication and general 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:94-108 (helper)

  Recursive helper to process Gmail message parts: base64-decodes text bodies (skips HTML unless flagged), recurses on nested parts, filters headers to essential ones (Date, From, To, etc.).

  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
  }