# Mock servers

> Return simulated API responses during a run with a mock server, from creating an endpoint to mock rules and reviewing what was mocked.

A mock server returns simulated API responses during a run, so a test does not have to call the real backend service. Mock servers work in dry runs, test plan executions, and local executions.

Mock servers are off until Testsigma support enables them for your account.

## Create a mock server

1. Go to **Test Data > Mock Servers**. The **Endpoints** page of the Mock Server application opens.

2. Click **Create Endpoint**.

3. Enter a subdomain for the endpoint on the **Create New Endpoint** page.

4. Click **Create**.

![The Create New Endpoint page of the mock server application, with the subdomain and Create](https://s3.amazonaws.com/website-static-docs.testsigma.com/new_images/projects/Updated_Doc_Images/Create_Mock_Server_with_Domain_Name.png)

## Use a mock server in a dry run

1. Go to **Create Tests > Test Cases** and open the test case.

2. Click **Run** in the action panel.

3. In the **Ad-Hoc Run** overlay, configure **Test Lab**, **Machine**, and **Environment**.

4. Expand **Additional Settings** and select the server from the **Mock Server** dropdown.

   ![Selecting a mock server in the Ad-Hoc Run overlay](https://s3.amazonaws.com/website-static-docs.testsigma.com/new_images/projects/Updated_Doc_Images/Select_Mock_Servers_in_AdHoc_Runs.png)

5. Click **Run Now**.

While the test runs, open the endpoint in the Mock Server application to watch the API calls arrive in real time.

## Use a mock server in a test plan

1. Go to **Test Plans** and open the plan.

2. Go to **Test Plan Settings**.

3. Select the server from the **Mock Server** dropdown under **Additional Settings**.

4. Click **Update**, or **Create** for a new plan.

5. Click **Run Now**.

## Review what was mocked

After a run, open the results page, click **More Details**, go to **Machine Details**, and select the mock server used. The **Mock Server History** section lists the rules that matched.

![The Mock Server History section on the run results page](https://s3.amazonaws.com/website-static-docs.testsigma.com/new_images/projects/Updated_Doc_Images/Mock_Server_History.png)

## Add a mock rule

A mock rule decides which API calls the server intercepts and what it returns. Rules are created from the calls a real run made, so run the test once first.

1. Open the test case results page and click **More Details**.

2. Go to **Machine Details** and select the mock server used.

3. Find the API call you want to mock in the **API Results** table, and click **Create Rule** in its **Action** column.

4. Update the rule details in the **Mock Rules** dialog.

5. Click **Save**.

The server returns the configured response for matching calls from the next execution onward.

Request matching and response configuration are documented by the mock server application itself, under Mock Rules and API Routes at `https://app.mockserver-us.testsigma.com/docs/beeceptor-features/`.