Gmail MCP

Instructions

Implementation Reference

• src/index.ts:763-786 (handler)

  Handler function for the 'list_threads' tool. It invokes handleTool to authenticate, calls the Gmail API to list threads with given parameters, processes thread messages by decoding payloads if includeBodyHtml is true, and formats the response.

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

• src/index.ts:756-762 (schema)

  Zod input schema defining parameters for the list_threads tool: maxResults, pageToken, q (query), labelIds, includeSpamTrash, includeBodyHtml.

    maxResults: z.number().optional().describe("Maximum number of threads to return"),
    pageToken: z.string().optional().describe("Page token to retrieve a specific page of results"),
    q: z.string().optional().describe("Only return threads matching the specified query"),
    labelIds: z.array(z.string()).optional().describe("Only return threads with labels that match all of the specified label IDs"),
    includeSpamTrash: z.boolean().optional().describe("Include threads 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:753-787 (registration)

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

  server.tool("list_threads",
    "List threads in the user's mailbox",
    {
      maxResults: z.number().optional().describe("Maximum number of threads to return"),
      pageToken: z.string().optional().describe("Page token to retrieve a specific page of results"),
      q: z.string().optional().describe("Only return threads matching the specified query"),
      labelIds: z.array(z.string()).optional().describe("Only return threads with labels that match all of the specified label IDs"),
      includeSpamTrash: z.boolean().optional().describe("Include threads 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.threads.list({ userId: 'me', ...params })
  
        if (data.threads) {
          data.threads = data.threads.map(thread => {
            if (thread.messages) {
              thread.messages = thread.messages.map(message => {
                if (message.payload) {
                  message.payload = processMessagePart(
                    message.payload,
                    params.includeBodyHtml
                  )
                }
                return message
              })
            }
            return thread
          })
        }
  
        return formatResponse(data)
      })
    }
  )

• src/index.ts:50-80 (helper)

  Shared helper function used by all Gmail tools, including list_threads, to handle OAuth2 authentication, create Gmail client, execute the API call, and handle 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)

  Helper function to recursively process and decode message parts (base64 to utf-8), filter headers, used in list_threads handler to prepare thread messages.

  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
  }