# How Kerno works

Kerno maps your codebase, builds a test environment around it, generates a validation suite, and runs that suite on every code change to detect what changed.

{% code expandable="true" %}

```mermaid
  flowchart LR
      s1["1. Index codebase"] --> s2["2. Set up environment"] --> s3["3. Build baseline"] --> s4["4. Validate changes"] --> s5["5. Update baseline"]
```

{% endcode %}

{% stepper %}
{% step %}

#### Index your codebase <i class="fa-code">:code:</i>

Kerno parses every file and builds a SCIP-based dependency graph that maps every function, class, and endpoint to the code that produces it. The graph is stored locally and used to scope every validation to exactly the affected endpoints. See [Codebase indexing](/docs/core-concepts/codebase-indexing.md).
{% endstep %}

{% step %}

#### Set up your test environment <i class="fa-docker">:docker:</i>

Kerno analyzes your build files and generates a Dockerfile and Compose plan for your app and its real dependencies (databases, queues, caches), plus mocks for external services. [See Environment setup.](/docs/core-concepts/environment-setup.md)
{% endstep %}

{% step %}

#### Build a baseline of how your app behaves <i class="fa-clipboard-check">:clipboard-check:</i>

Kerno generates test scenarios for each endpoint covering functional behavior, edge cases, error handling, and auth. It runs them against your live stack and captures the responses as\
the baseline. This is the reference point for every future validation. See [Scenarios and baselines](/docs/core-concepts/scenarios-and-baselines.md)
{% endstep %}

{% step %}

#### Validate every change <i class="fa-vial-circle-check">:vial-circle-check:</i>

When you change code, Kerno uses the dependency graph to detect the blast radius and re-runs only the affected scenarios. It compares responses against the baseline and surfaces any diffs. If the diff is intentional, accept it and Kerno updates the baseline. If it is not, fix your code and run validation again.
{% endstep %}

{% step %}

#### Maintain everything <i class="fa-sparkles">:sparkles:</i>

As your codebase evolves, Kerno updates your environment, adds scenarios for new endpoints, retires stale ones, and heals tests when contracts change. Everything stays current without manual intervention.
{% endstep %}
{% endstepper %}


---

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