Validation Layers

Why layers matter in Let Books

No single validation method is enough.

• documentation alone does not enforce behavior
• tests alone may validate the wrong assumptions
• CI alone cannot define the rules it is supposed to enforce

A layered approach is stronger because each layer catches a different class of drift.

Common validation layers

1. Specification and guidance

The first layer defines the rule.

Without this layer, later checks may be strict but arbitrary.

2. Manual review

Human review checks intent, edge cases, and product meaning that may not yet be automated.

3. Local validation

Scripts and structured checks catch fast, repeatable issues before changes reach CI.

4. Tests

Executable tests verify expected behavior, but only when they are aligned with the spec.

5. CI gates

CI makes checks repeatable and visible across contributors and environments.

6. Deployment checks

Deployment workflows confirm that the built artifacts are still publishable and structurally sound.

How the layers should relate

The layers should reinforce each other in order:

• docs and specs define expectations
• review interprets those expectations in context
• validation scripts and tests automate stable parts of the review
• CI runs those checks consistently
• deployment ensures the output can actually ship

Good early validation targets

Examples of strong early candidates include:

• required-file presence
• localization completeness
• syntax validity
• broken internal links
• forbidden editorial citations
• metadata generation success

These checks tend to be objective and inexpensive.

Let Books context

The Let Books repository already documents several layers, including:

• product and implementation rules in AGENTS.md and AGENTS-Implementation.md
• development and deployment validation in docs/Development.md and docs/Deployment.md
• editorial evidence rules in docs/blog/README.md and docs/sources/README.md
• learning guidance for staged CI and validation rollout

That makes validation a documented system rather than only a future aspiration.