Gmail MCP

Instructions

Implementation Reference

• src/index.ts:652-673 (handler)

  The handler function for the 'send_message' tool. It constructs the raw email message if not provided, sends it using the Gmail API, processes the response payload to decode bodies if requested, and formats the output.
  async (params) => { return handleTool(config, async (gmail: gmail_v1.Gmail) => { let raw = params.raw if (!raw) raw = await constructRawMessage(gmail, params) const messageSendParams: MessageSendParams = { userId: 'me', requestBody: { raw } } if (params.threadId && messageSendParams.requestBody) { messageSendParams.requestBody.threadId = params.threadId } const { data } = await gmail.users.messages.send(messageSendParams) if (data.payload) { data.payload = processMessagePart( data.payload, params.includeBodyHtml ) } return formatResponse(data) }) }
• src/index.ts:642-651 (schema)

  Zod schema defining the input parameters for the 'send_message' tool, including optional raw message, recipients, subject, body, thread ID, and HTML inclusion flag.
  { 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 message 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:640-674 (registration)

  Registers the 'send_message' tool on the MCP server with name, description, input schema, and handler function.
  server.tool("send_message", "Send an email message to specified recipients. 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 message 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 messageSendParams: MessageSendParams = { userId: 'me', requestBody: { raw } } if (params.threadId && messageSendParams.requestBody) { messageSendParams.requestBody.threadId = params.threadId } const { data } = await gmail.users.messages.send(messageSendParams) if (data.payload) { data.payload = processMessagePart( data.payload, params.includeBodyHtml ) } return formatResponse(data) }) } )
• src/index.ts:200-235 (helper)

  Helper function to construct the base64url-encoded raw RFC 2822 email message from parameters, including handling thread quoting and text wrapping.
  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: ${wrapTextBody(params.subject)}`) } else { message.push('Subject: (No Subject)') } message.push('Content-Type: text/plain; charset="UTF-8"') message.push('Content-Transfer-Encoding: quoted-printable') message.push('MIME-Version: 1.0') message.push('') if (params.body) message.push(wrapTextBody(params.body)) if (thread) { const quotedContent = getQuotedContent(thread) if (quotedContent) { message.push('') message.push(wrapTextBody(quotedContent)) } } return Buffer.from(message.join('\r\n')).toString('base64url').replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '') }
• src/index.ts:50-80 (helper)

  Shared helper for all tools: manages authentication, creates Gmail client, executes the API call, and formats errors especially for auth issues.
  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}` }); } }