Connect with MCP

The builders.ac MCP server lets compatible AI clients manage workspaces, domains, personas, inboxes, and operations through the complete Provisioning API toolset. It is hosted and managed by builders.ac, so there is no package to install and no local server to keep running.

Provisioning is for internal testing only

The Provisioning API is not supported yet. These MCP tools are available for internal testing only and must not be used for production workflows.

Server URL

Streamable HTTP

https://mcp.builders.ac/mcp

The /mcp path is the Streamable HTTP transport endpoint. Use the complete URL shown above.

Connect your agent

OAuth is the recommended connection method. On the first connection, your client opens a browser so you can sign in to builders.ac and approve access. You do not need to create or paste an API Key or API Secret for OAuth. Retrieving encrypted inbox or domain credentials requires an API-key connection; see Encrypted responses.

Chat clients

ChatGPT

1. In ChatGPT, open Settings → Security and login and enable Developer mode.
2. Open Plugins, select the plus button, and create a connection named builders.ac.
3. Under Connection, enter the server URL shown above.
4. Create the connection, complete the browser authorization, and review the discovered tools.
5. Start a new chat and add builders.ac from the tools menu.

Developer mode and custom connections can be limited by your ChatGPT plan or workspace policy. See Connect and test an MCP server in ChatGPT.

Claude

1. Open Customize → Connectors in Claude.
2. Select the plus button, then Add custom connector.
3. Name it builders.ac and paste the server URL shown above.
4. Select Connect, then finish signing in and approving access in your browser.

On Team or Enterprise, an owner must first add the connector under Organization settings → Connectors. These steps use Claude’s native remote connector; no local proxy is required.

See Use a custom remote MCP connector in Claude.

Coding agents and IDEs

Claude Code

Add the remote HTTP server:

Terminal

claude mcp add --transport http builders-ac https://mcp.builders.ac/mcp

Start Claude Code, run /mcp, select builders-ac, and complete the browser authorization. Use claude mcp list later to check the connection.

See Connect Claude Code to tools with MCP.

Codex

Add the remote server, then start its OAuth flow:

Terminal

codex mcp add builders-ac --url https://mcp.builders.ac/mcp
codex mcp login builders-ac

Run codex mcp list to confirm that builders-ac is configured. The CLI and IDE extension share the same MCP configuration.

See Connect Codex to MCP servers.

Cursor

Add this to .cursor/mcp.json for one project, or ~/.cursor/mcp.json to make it available across projects:

mcp.json

{
  "mcpServers": {
    "builders-ac": {
      "url": "https://mcp.builders.ac/mcp"
    }
  }
}

Open Cursor’s MCP settings, connect builders-ac, and complete the browser authorization. These instructions target the Cursor desktop app.

See Cursor’s MCP documentation.

Other clients

Configure a remote Streamable HTTP MCP server with the URL shown above and choose OAuth when your client asks for an authentication method. In addition to OAuth discovery and dynamic client registration, the client must use an HTTP loopback callback on localhost, 127.0.0.1, or [::1]. Other hosted callback domains are not accepted.

If your client asks for the transport separately, choose Streamable HTTP, not SSE or stdio.

Try it

After connecting, ask your client:

• “Which builders.ac account am I connected as?”
• “List my workspaces.”
• “Show the personas in my workspace.”
• “List my provisioning operations and their status.”

For the complete setup lifecycle, follow Set Up Your Sending Infrastructure with AI. It covers owned domains, nameservers, mailbox creation, sequencer connections, and the manual warmup checkpoint, with the same internal-testing limitations.

Available tools

The server exposes 47 tools: all 44 Provisioning operations and three helpers. The default tools/list response includes the entire current catalog. Provisioning names and input schemas come from the OpenAPI contract, using its operation IDs as tool names. See the Provisioning guide for resource behavior.

Area	Tools
Helpers	me, sending_ac_info, provisioning_api_key_setup
Account	getAuthenticatedAccount, listEncryptionKeys
Meta	getApiIndex, getProvisioningOpenApi, getProvisioningProblem, listProvisioningProblems
Workspaces	listWorkspaces, createWorkspace, getWorkspace, updateWorkspace, deleteWorkspace, archiveWorkspace, unarchiveWorkspace
Personas	listPersonas, createPersona, getPersona, updatePersona, deletePersona
Domains	listDomains, getDomain, updateDomain, deleteDomain, connectDomains, reconnectDomain, buyDomains, renewDomain, setDomainRedirect, cloneDomain, setDomainSequencer, removeDomainSequencer
Inboxes	listInboxes, createInboxes, getInbox, updateInbox, deprovisionInboxes, uploadInboxes
Provider accounts	listProviderAccounts, createProviderAccount, getProviderAccount, updateProviderAccount, deleteProviderAccount
Operations	listOperations, getOperation, cancelOperation

The three helpers take no arguments. me returns the connected user’s ID, name, and email; sending_ac_info describes builders.ac; provisioning_api_key_setup directs you to create a builders.ac API credential and reconnect using it.

MCP tools are invoked through tools/call. Let your client discover their schemas and call them. The server exposes tools only, with no MCP resources or prompts.

Inputs, results, and retries

Provisioning tools use the API’s path and query parameter names, such as wsp, dom, inb, and limit. JSON request fields go inside body. A required Idempotency-Key header becomes a required idempotency_key argument. For example, createWorkspace accepts:

{
  "idempotency_key": "a553bfc5-0651-4b21-a847-6d12507b7c9f",
  "body": { "name": "Outreach" }
}

Your agent can generate the idempotency key. Use a new key for a new intended operation and reuse the same key and arguments when retrying that operation. Changing the key on retry can create duplicate work. If an execution’s outcome is uncertain, check the resource or operation status before repeating a mutation.

createInboxes accepts up to 150 entries, but the resulting capacity-occupying total on the Domain must be exactly 50, 75, or 150. On a fresh Domain, request one of those totals; on an existing Domain, use the allowed_additions returned with domain_inbox_count_invalid to choose a tier-valid top-up. Paid-slot availability is a separate check.

Provisioning results contain status, relevant response headers, and the API body. Validation, tenant access, feature flags, rate limits, pagination, and idempotency follow the API. HTTP errors appear as tool errors. Asynchronous actions return operation data and a Location header when the API supplies one; use getOperation to check progress. Domain purchase (buyDomains) and renewal (renewDomain) currently return 501.

Destructive operations

deleteWorkspace, deletePersona, deleteDomain, deprovisionInboxes, removeDomainSequencer, and deleteProviderAccount execute when called. They carry destructiveHint: true, so your AI client may show its own approval dialog. The MCP server does not add a confirmation page, typed confirmation, or proof challenge. An API Secret is not needed for destructive MCP calls.

Direct HTTP calls to the Provisioning API still require its sealed-proof flow for these operations. That requirement applies to the public API, not the authenticated MCP tools.

Encrypted responses

getInbox and getDomain require API-key authentication because their responses can contain credentials encrypted for that API Key. MCP returns the same encrypted fields as the API. Decrypt the ciphertext locally with the corresponding API Secret if you need to read it. There is no browser secret-view page, and the AI client receives no decrypted credential values from these responses.

OAuth calls to either tool return api_key_required before the operation runs, with a link to create a builders.ac API credential. Reconnect through a client that supports API-key bearer authentication to use those tools. You can also call provisioning_api_key_setup for these instructions.

Verify with MCP Inspector

MCP Inspector is useful when you want to test the server independently of an AI client.

1. Start the Inspector:

   npx @modelcontextprotocol/inspector@latest

2. Open the local URL printed in your terminal.

3. Select Streamable HTTP, enter the builders.ac server URL, and select Connect.

4. If authentication is requested, open Auth settings, run the quick OAuth flow, then connect again.

5. Select List Tools. You should see all 47 tools, including listWorkspaces, deleteWorkspace, and provisioning_api_key_setup.

Authentication details

Interactive MCP clients should use OAuth. The client discovers the builders.ac authorization server, registers itself, and uses authorization code with PKCE. Access is limited to the mcp:use scope, and a compatible client manages access and refresh tokens for you. OAuth resolves your Provisioning account automatically on first use; there is no key-generation or key-download step during consent.

Clients that support bearer authentication may instead send an existing Provisioning API Key. Configure this in the client’s authentication settings:

Authorization: Bearer age1…

Send only the API Key. Never send the API Secret to the MCP server or store it in an MCP client configuration.

Troubleshooting

What you see	What it means	What to do
405 Method Not Allowed in a browser	Browsers send GET; the MCP transport uses POST	Connect through an MCP client or MCP Inspector
404 Not Found at the hostname root	The transport endpoint is at /mcp	Use the complete server URL shown above, including /mcp
The browser authorization does not open	The client did not start OAuth	Choose OAuth, reconnect, or verify with MCP Inspector
api_key_required	getInbox or getDomain was called through OAuth	Request an API Key with provisioning_api_key_setup and reconnect using it
The tools are missing or stale	The client cached older server metadata	Refresh or rescan the connection, then start a new chat
The client supports only SSE or local MCP	It cannot use this Streamable HTTP endpoint	Use a client with native Streamable HTTP and OAuth support
Authorization repeatedly fails	The client’s saved session may be stale	Disconnect, clear the builders-ac authorization, and connect again

Opening the server URL in a browser is not a health check. A 405 response there is expected; listing tools through MCP Inspector is the definitive connection test.