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Publish your API as an MCP server

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At the end of this tutorial, Claude creates a contact in Nimbus CRM through a gateway of yours. Before the contact is created, Claude shows a confirmation card and waits for you to approve it.

Nimbus CRM is the example app of these docs: a CRM with contacts, companies and deals, and a REST API under /api. The code is at github.com/faustine-ai/example-nimbus-crm.

In this tutorial, you:

Before you begin

  • A Faustine workspace with a model provider connected. See Connect your model provider.
  • Nimbus CRM running at a URL that Faustine can reach over the internet. A server on localhost is not reachable.
  • An account on claude.ai that can add custom connectors.

Create the API and run the analysis

A gateway serves APIs that Faustine has analyzed. Analyze your first API covers this part step by step on Nimbus CRM. Follow it to the end, then come back. In short:

  1. In the portal, go to APIs and select New API.
  2. Name the API Nimbus CRM and connect your fork of the repository. The wizard sets the namespace to nimbuscrm.
  3. Start the analysis and wait for it to finish.
  4. In the API's Connections tab, add a connection with the base URL of your Nimbus CRM server and the seeded account from its README. See Add a connection.

The API's Operations tab lists the operations the analysis found, among them one that creates a contact with POST /api/contacts.

Require confirmation to create a contact

The analysis marks destructive writes, such as deletes, as requiring confirmation. Creating a contact is not one of them, so you mark it yourself.

  1. In the API's Operations tab, find the operation that creates a contact.
  2. In the Requires confirmation column, turn the switch on.
  3. Select Save changes.
  4. Select Publish in the API's header.

The flag belongs to the API. Every gateway that serves this version applies it. See Mark an operation as requiring confirmation.

Create the gateway and a gateway user

  1. Go to Agent Gateway and select New Gateway.

  2. Under Who is this gateway for?, select People using chat and coding agents.

  3. Under APIs, select Nimbus CRM, then Continue.

  4. Under Name & URL, enter Nimbus CRM in Name. The Slug becomes nimbus-crm. Copy the address in MCP URL, then select Continue.

    https://gateway.faustine.ai/<workspace>/nimbus-crm/mcp

  5. Under First credential, select A user. Enter your name in Display name. The Username is filled in from it. Keep the generated password.

  6. Select Continue. The review shows the gateway's name, its URL, the API and the user.

  7. Select Create gateway.

  8. Copy the username and the password from the dialog. The password is shown once.

The gateway opens on its Overview tab. The setup path there shows Add an API, Choose the operations and Create a key or a user as done, and Connect a client as the next step.

The user you created is set to Ask the person: when a client calls an operation that requires confirmation, the call waits for the person. You can see it in Access > Users, on the user's page, under Confirmation.

Choose the operations

The operations of the API start exposed, except recipes. For this tutorial, hide the deletes so that Claude cannot call them.

  1. Select the Operations tab.
  2. In Search operations…, enter delete.
  3. Select Hide matching.
  4. Select Save changes.

The counter above the table shows how many operations are exposed. The operation that creates a contact is still among them.

Connect Claude

  1. In claude.ai, go to Settings > Connectors and select Add custom connector.
  2. Enter Nimbus CRM as the name and paste the MCP URL.
  3. Leave the OAuth client ID and client secret fields empty.
  4. Connect. A browser window opens on the gateway's sign-in page.
  5. Enter the username and the password of the gateway user.

Claude lists four tools for the connector: search_operations, get_operation and run_code, plus review_pending, which shows the confirmation card. The gateway serves in Code mode, where Claude looks up the operations it needs and writes a short script that calls them. See Connect Claude Desktop and claude.ai for more on this client.

Create a contact and approve it

  1. Start a conversation in claude.ai with the connector turned on.

  2. Send this message:

    Add Ada Lovelace ([email protected]) as a contact in Nimbus CRM.

  3. Allow Claude to use the connector's tools when it asks.

Claude searches the operations, reads the schema of the one that creates a contact, and runs a script that calls it. The gateway does not run the call. It pauses the script, and Claude shows the Faustine confirmation card in the conversation.

The card is titled Approve this operation?. It names the operation and shows the arguments Claude sent. Nothing has run at this point.

  1. Select Approve.

Checkpoint

The card changes to Done and Claude reports that the contact was created. In Nimbus CRM, Ada Lovelace is in the contacts list. If you select Reject all instead, nothing runs and no contact is created.

Find the request in Logs

  1. In the portal, open the gateway's Logs tab. The list shows the requests of the conversation, newest first. The Actor is your gateway user.
  2. Select the run_code request. Its page shows the script Claude wrote.
  3. Go back and select the decide_pending request, which is your approval. Its page shows the call to the operation that creates a contact and, under it, the exchange with your server: POST /api/contacts with the status Nimbus CRM answered.

Every request has an ID that starts with req_. Your server received the same ID in the x-request-id header.

Requests for search_operations and get_operation are discovery calls. To see them, turn on Show discovery calls under More.

What you built

Your workspace has a gateway named Nimbus CRM that serves the Nimbus CRM API over MCP and REST, with one gateway user. It is listed under Agent Gateway, and every call made through it is in its Logs tab.

Next steps

Last updated November 11, 2026