One server, five ways in

Every platform below connects to the same address, https://api.billingmart.com/mcp, and signs in with OAuth 2.1 and PKCE. You sign in as yourself, choose the workspace, and tick the access the assistant may have. It can never hold more than your role allows, and anything that sends a message or moves money still waits for a person to approve it.

What is checked, and what is not. The server side: the discovery documents, client registration for the hosts below, the consent page and the tool list, is exercised by our own test suite on every change. The menus and button names inside each assistant belong to that product and change without notice. We have not yet walked these pages through on a fresh account for each platform, so every platform step carries a note saying so. These pages were written on 9 October 2026.

1. In Claude, open Settings, then Connectors, and choose Add custom connector.
2. Paste https://api.billingmart.com/mcp and add it. Claude registers itself with the server on its own.
3. Sign in to BillingMart in the window that opens, choose the workspace and the access, and pick Ask (the default) or Plan.

Not yet run against the platform. Claude is on the server’s list of verified hosts, so the consent page shows it as verified. The menu names above are from our setup notes.

claude mcp add --transport http billingmart https://api.billingmart.com/mcp

Start Claude Code and use its /mcp command to sign in; a browser window opens on the same consent page.

Not yet run against the platform. The command is the one Claude Code documents for a remote HTTP server. We have not run it against the current release.

1. Turn on Developer mode in ChatGPT’s settings (a plan that has it is required).
2. Add a connector, give it the address https://api.billingmart.com/mcp, and choose OAuth.
3. Sign in to BillingMart, choose the workspace and the access.

For plain chat, ChatGPT needs two tools named search and fetch. We provide both: search looks across invoices, estimates and clients and returns titles with links, and fetch returns one record as text with a link to it in the console.

Not yet run against the platform. ChatGPT’s hosts are on the verified list. Where Developer mode sits in the settings, and which plans have it, are OpenAI’s to say and may differ from this page.

These take a connector added by an administrator, over Streamable HTTP, with a client you registered ahead of time rather than one the assistant creates for itself. A workspace owner or admin registers that client for the workspace; it is a confidential client bound to that one workspace, its secret is shown once, and consent for any other workspace is refused.

1. As a BillingMart owner or admin, register a client for the workspace and keep the id and secret.
2. As the Gemini administrator, add a custom MCP connector with https://api.billingmart.com/mcp, the client id and the client secret.
3. Each person then signs in to BillingMart from Gemini and chooses their access.

Not yet run against the platform. We have not run this against a Gemini Enterprise tenant, nor a Gemini Business one. Where the owner registers the client in the console, and the names of the fields on Google’s side, are unconfirmed.

The Gemini CLI can read a remote server from its settings file and discover the sign-in itself, or take a token you already hold.

{
  "mcpServers": {
    "billingmart": { "httpUrl": "https://api.billingmart.com/mcp" }
  }
}

Not yet run against the platform. This follows the Gemini CLI’s documented shape for a remote server; we have not run it, and the sign-in step is unconfirmed.

We make no claim about the consumer Gemini app, either way. This page will say more when we have checked.

The assistant’s tool list is built from what you ticked, so a read-only connection lists no write tools. You can narrow or remove the connection at any time under Connected apps in the console. The rules for modes, approvals and tenant text are on the MCP server guide.