Gmail MCP

Instructions

Implementation Reference

• src/index.ts:262-296 (registration)

  Registration of the 'create_draft' tool using McpServer.tool(), including description, input schema, and inline handler function.

  server.tool("create_draft",
    "Create a draft email in Gmail. Note the mechanics of the raw parameter.",
    {
      raw: z.string().optional().describe("The entire email message in base64url encoded RFC 2822 format, ignores params.to, cc, bcc, subject, body, includeBodyHtml if provided"),
      threadId: z.string().optional().describe("The thread ID to associate this draft with"),
      to: z.array(z.string()).optional().describe("List of recipient email addresses"),
      cc: z.array(z.string()).optional().describe("List of CC recipient email addresses"),
      bcc: z.array(z.string()).optional().describe("List of BCC recipient email addresses"),
      subject: z.string().optional().describe("The subject of the email"),
      body: z.string().optional().describe("The body of the email"),
      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) => {
        let raw = params.raw
        if (!raw) raw = await constructRawMessage(gmail, params)
  
        const draftCreateParams: DraftCreateParams = { userId: 'me', requestBody: { message: { raw } } }
        if (params.threadId && draftCreateParams.requestBody?.message) {
          draftCreateParams.requestBody.message.threadId = params.threadId
        }
  
        const { data } = await gmail.users.drafts.create(draftCreateParams)
  
        if (data.message?.payload) {
          data.message.payload = processMessagePart(
            data.message.payload,
            params.includeBodyHtml
          )
        }
  
        return formatResponse(data)
      })
    }
  )

• src/index.ts:274-295 (handler)

  Core handler logic for 'create_draft': handles raw message construction, calls Gmail drafts.create API, processes the response payload, and formats it.

  async (params) => {
    return handleTool(config, async (gmail: gmail_v1.Gmail) => {
      let raw = params.raw
      if (!raw) raw = await constructRawMessage(gmail, params)
  
      const draftCreateParams: DraftCreateParams = { userId: 'me', requestBody: { message: { raw } } }
      if (params.threadId && draftCreateParams.requestBody?.message) {
        draftCreateParams.requestBody.message.threadId = params.threadId
      }
  
      const { data } = await gmail.users.drafts.create(draftCreateParams)
  
      if (data.message?.payload) {
        data.message.payload = processMessagePart(
          data.message.payload,
          params.includeBodyHtml
        )
      }
  
      return formatResponse(data)
    })
  }

• src/index.ts:265-273 (schema)

  Zod schema defining input parameters for the 'create_draft' tool.

    raw: z.string().optional().describe("The entire email message in base64url encoded RFC 2822 format, ignores params.to, cc, bcc, subject, body, includeBodyHtml if provided"),
    threadId: z.string().optional().describe("The thread ID to associate this draft with"),
    to: z.array(z.string()).optional().describe("List of recipient email addresses"),
    cc: z.array(z.string()).optional().describe("List of CC recipient email addresses"),
    bcc: z.array(z.string()).optional().describe("List of BCC recipient email addresses"),
    subject: z.string().optional().describe("The subject of the email"),
    body: z.string().optional().describe("The body of the email"),
    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 that manages OAuth2 authentication, validates credentials, creates Gmail client, executes the API call, and handles errors including auth-specific 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:200-235 (helper)

  Helper function to construct the base64url-encoded RFC 2822 raw email message, handling thread quoting and headers if threadId provided.

  const constructRawMessage = async (gmail: gmail_v1.Gmail, params: NewMessage) => {
    let thread: Thread | null = null
    if (params.threadId) {
      const threadParams = { userId: 'me', id: params.threadId, format: 'full' }
      const { data } = await gmail.users.threads.get(threadParams)
      thread = data
    }
  
    const message = []
    if (params.to?.length) message.push(`To: ${wrapTextBody(params.to.join(', '))}`)
    if (params.cc?.length) message.push(`Cc: ${wrapTextBody(params.cc.join(', '))}`)
    if (params.bcc?.length) message.push(`Bcc: ${wrapTextBody(params.bcc.join(', '))}`)
    if (thread) {
      message.push(...getThreadHeaders(thread).map(header => wrapTextBody(header)))
    } else if (params.subject) {
      message.push(`Subject: ${wrapTextBody(params.subject)}`)
    } else {
      message.push('Subject: (No Subject)')
    }
    message.push('Content-Type: text/plain; charset="UTF-8"')
    message.push('Content-Transfer-Encoding: quoted-printable')
    message.push('MIME-Version: 1.0')
    message.push('')
  
    if (params.body) message.push(wrapTextBody(params.body))
  
    if (thread) {
      const quotedContent = getQuotedContent(thread)
      if (quotedContent) {
        message.push('')
        message.push(wrapTextBody(quotedContent))
      }
    }
  
    return Buffer.from(message.join('\r\n')).toString('base64url').replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '')
  }