check-impl-against-spec

SKILL.md

Check implementation against spec

Use this skill only when spec_context.md exists during PR review.

Goal

Determine whether the implementation in the checked-out PR materially matches the approved spec context. This is a supplement to the normal code review, not a separate output.

Inputs

spec_context.md contains the spec context to compare against. It may include both product spec content (intended behavior, acceptance criteria) and tech spec content (implementation details, file changes).

pr_diff.txt contains the annotated diff for the PR.

pr_description.md may contain additional scope or rationale.

The working tree contains the PR branch contents.

Process

Read spec_context.md and extract the concrete commitments it makes:

required behaviors (from the product spec)

required files or subsystems to change (from the tech spec)

stated constraints

required follow-up steps, validation, or migrations

Compare those commitments against the actual implementation in pr_diff.txt and the checked-out files.

Treat small implementation-level adjustments as acceptable when they preserve the spec's intent. Do not flag harmless differences in naming, structure, or low-level technique.

Flag a mismatch only when it is material, such as:

required behavior in the product spec is missing

the implementation contradicts a spec decision

the change introduces significant unplanned scope

a required validation, migration, or compatibility step from the tech spec is absent

Outputs

Do not create a separate report file.

Fold spec-alignment findings into review.json.

Put broad spec-drift concerns in the review summary.

Add inline comments only when the mismatch can be tied to changed lines in the diff.

Treat material spec drift as at least an important concern.

If the implementation matches the spec closely enough, do not add comments just to mention alignment.

Boundaries

Do not require literal one-to-one implementation of the spec when the PR achieves the same outcome safely.

Do not speculate about spec details that are not actually present in spec_context.md.

Do not post to GitHub directly.