# Defining a mock API
For a rule-based database, you define the mock API on the database **API** tab.
By default, the **API** tab contains a commented-out example mock API definition.
Default view of the API tab for a database
## Populating the mock API definition directly
One option is to enter the mock API definition directly in the definition field.
For information on the API syntax, go to [mock-api-reference](https://docs.tonic.ai/fabricate/database-mock-api/mock-api-reference "mention").
After you populate the definition, to save it, click **Save**.
## Using Fabricate AI to generate the mock API definition
To use the Fabricate AI to generate the mock API definition:
1. Click **Compose with AI**.
2. On the **Compose with API** panel, provide a description of the calls to include in the mock API, then click **Generate**.
3. To add the generated results to the mock API, click **Add to API**.
Compose with API panel with calls generated by AI based on descriptions
4. On the **API** tab, to save the new definition content, click **Save**.
## Tracking the change history for the mock API definition
Every time to save the mock API definition, Fabricate adds an entry to the definition history.
You can view the changes for each saved version, and revert to a previous version.
### Displaying the change history
On the **API** tab, to display the change history, click **History**.
The **History** panel lists the versions in reverse chronological order, with the current version at the top.
When you click a version, Fabricate shows the differences from the previous version, including new and removed content.
Change history for a mock API definition
### Reverting to a previous version
To revert the mock API definition to a previous version:
1. In the version list, click the version to revert to.
2. Click **Revert to This Version**.
