10 min

# Add the ontology files

A git-managed project needs one complete ontology tree in the repository. Usually, you pull the ontology Cassis already created and commit it.

## If the project already has an ontology

1.  Install the [Cassis CLI](/build/cli/) and set `CASSIS_API_KEY`.
    
2.  From the repository checkout, pull the current ontology:
    
    ```bash
    cassis ontology pull --project <project-id>
    ```
    
    This creates the `cassis/` directory, including `project.yml`, the ontology files, and the generated `AGENTS.md` modeling guide. `project.yml` binds later commands to the project.
    
3.  Validate the files:
    
    ```bash
    cassis ontology fmt
    cassis ontology check
    ```
    
4.  Review the diff, then commit the complete `cassis/` directory.
    

## If you are starting from scratch

Copy the [`cassis/` directory from the minimal example](https://github.com/GetCassis/cassis-ontology-examples/tree/main/examples/minimal) into the repository. Update it for your warehouse, then run:

```bash
cassis ontology fmt
cassis ontology check
```

Commit the result when it passes. The [modeling guide](/build/cli/#the-modeling-guide) explains how people and coding agents should structure the content, while the [schema reference](/reference/schema/) defines every field.

Keep only ontology files under the configured `cassis/` path. An import treats that directory as the complete ontology: adding a file adds an object, and deleting a file deletes it.

## Next

[Connect the repository](/build/git-connect/), then [protect changes with CI](/build/ci/).