---
name: principle-prove-it-works
description: "Apply after completing a task, before declaring done. Verify against the real artifact (run the feature, read the actual value, inspect the diff), not a proxy, self-report, or 'it compiles.'"
disable-model-invocation: true
---

# Prove It Works

Before declaring done, check the requested outcome against the real artifact.

- Run the changed behavior, read the stored value, or inspect the produced file, as the task requires. Compilation and passing checks prove only what they cover.
- Confirm you are observing the current build, instance, or output. Investigate a surprising result before blaming either the system or the check.
- For a mutation, verify the resulting state; an acknowledgement alone is insufficient.
- Show the evidence for each state or case you checked: how you observed it (screenshot, recording, DOM or value reading, command output) and what you saw. Prefer a capture; when captures are unreliable, say so and quote the reading.
- Name what you did not check, including any item on the project's done checklist. An unavailable check is a gap, not a pass. "Checked in light and dark" with nothing behind it, and silence about unchecked reduced motion, both fail this rule.

Use the smallest rerunnable script when it makes the proof more reliable or reusable. Keep evidence reviewable and outside cleanup paths; commit it when the deliverable needs a lasting audit trail.