JohnJackHouzi Prove it
A passing type-check is not proof. A read of the source is not proof. An agent's report is not proof. Proof is an artifact captured from the running system after the change.
This skill turns "it should work" into either evidence or an honest admission.
The rule
Never claim a change works until you have captured an artifact from the running system that would look different if the change were broken.
The counterfactual is the whole test. If your evidence would look identical on a
broken build, it is not evidence. tsc passes on a page that 500s. grep finds a
tracking snippet that a CSP silently blocks. A subagent reports six files fixed
that were never written to disk.
Procedure
1. State the claim. One sentence, falsifiable, naming the environment. Bad: "the fix works". Good: "GET https://example.com/pricing returns 200 and the page contains 'Pro plan' on production."
2. Pick the evidence. Use the table below. If two kinds are cheap, take both: one positive (the new behaviour appears) and one negative (no console error, no failed request).
3. Capture it. Run a tool, save the output to a file. Never paraphrase from memory - quote the captured bytes.
4. Return a verdict. PROVEN, NOT PROVEN, or UNPROVABLE HERE, with the
artifact path and the decisive line. Never end a task with an unqualified
"done" when the verdict is anything other than PROVEN.
Evidence table
| Claim | Minimum acceptable proof | Tool |
|---|---|---|
| A page loads / renders | HTTP status + a string from the new markup | scripts/capture_http.sh |
| A client-side feature works | Browser console clean + expected DOM text | scripts/capture_page.mjs |
| Analytics, pixel, or beacon fires | The outbound network request, captured, with its status | scripts/capture_page.mjs --expect-request |
| An API behaves | Request and response body, both saved | scripts/capture_http.sh --data |
| A visual change | Screenshot taken after the deploy, at a stated viewport | scripts/capture_page.mjs --screenshot |
| A bug is fixed | The exact reproduction from before, now producing the new result | reuse the original repro command |
| A build or deploy landed | Deployed commit SHA or build id read back from the live system | curl a version endpoint, or the host's CLI |
| A migration applied | A query against the real database showing the new shape | the project's DB client |
| A file was produced | Read the produced file back and quote from it | Read the output, not the generator |
| A test suite passes | The runner's own summary line, unedited | the test command |
Full recipes, including the traps for each row: references/proof-recipes.md.
What is never proof
Reading these back to the user as evidence is the single most common failure mode.
The full list with the reasoning: references/fake-proofs.md.
- A type-check, a lint, or a build that compiles
- Reading the source you just wrote
grepfinding a string in a repo- A subagent's summary that you did not verify on disk
- "The logic is correct, so it works"
- A screenshot or log captured before the deploy finished
- The absence of an error you never looked for
Tools
All scripts are dependency-light and write their evidence to .prove-it/ in the
project root. They exit non-zero when an expectation is not met, so they can be
chained or run in CI.
# HTTP: status, redirects, timing, headers, body assertion
scripts/capture_http.sh https://example.com/pricing --expect-text "Pro plan"
# Browser: console errors, network requests, DOM text, screenshot
node scripts/capture_page.mjs --url https://example.com \
--expect-request 'facebook\.com/tr' --expect-text "Pro plan" --screenshot
# Ledger: record verdicts, print the report to paste back to the user
python3 scripts/proof_ledger.py add --claim "..." --verdict PROVEN --evidence .prove-it/http-....json
python3 scripts/proof_ledger.py report
capture_page.mjs needs Playwright. If it is missing, the script prints the exact
install command and exits 2 - report UNPROVABLE HERE rather than substituting a
weaker proof, unless another browser tool is available in the session.
When you cannot prove it
Say so, in one line, immediately, and name what is missing:
NOT PROVEN - no credentials for the staging database, so the migration was never read back. The code is written and the type-check passes; that is all I verified.
An honest UNPROVABLE HERE is a good outcome. A confident "done" that was never
checked is the failure this skill exists to prevent. Do not soften it, do not bury
it at the end of a paragraph, and do not let a green build stand in for it.
Verdict format
Close every verification with the block described in references/verdict-format.md.
It is three lines: claim, verdict, artifact.