Verify

One of Tap’s three primitive planes. Verify takes a plan and the rows it produced and answers: is this still right? Without Verify, Replay is just a compiler that quietly emits the wrong answer when the world changes.

What Verify is for

Verify solves T3 (a system can’t detect its own staleness) and D3 (rules evolve), and enforces eternal-principle 1 (correctness must not depend on any single entity). Replay alone is not enough — Replay only knows what its plan says, and the plan can become quietly wrong.

The framing in ADR 2026-04-26 — Three-Plane Refactor:

Tap is a differential-testing-equipped compiler for stateful external systems whose outputs decay over time.

Verify is the “differential-testing-equipped” half of that sentence.

What lives in Verify

Tool Source IRI Role
tap verify [<site>/<name>] https://taprun.dev/verify 4-layer cross-validation against the live page
V (verifier) (internal) strict pass/fail against an authoritative source (fetch-json / fetch-json-2step / fetch-atom)
fingerprint (internal) site-shape baseline; flags STALE state on diff
heal-cache (internal) site-scoped cache of {old_fragment, new_fragment} patches replayed at 0 LLM tokens
schedule / watch (internal) continuous monitoring; fires Verify on a cadence

The 4-layer cross-validation

tap verify runs the plan output against four independent sources in descending trust:

  1. JSON-LD / schema.org / Annotation / RDFa — canonical machine-emitted data
  2. API JSON — the network response the page itself fetches
  3. Semantic HTML — <article>, <h1>, <address>, ARIA roles
  4. CSS / structural classes — last resort

When higher-trust layers disagree with the layer the plan currently uses, Verify emits a tap:DriftReport annotation. The drift report is itself a W3C Annotation envelope that any tool can consume.

The lifecycle Verify owns

State tap.health fingerprint Verify action
HEALTHY PASS match none
BROKEN FAIL any heal (= Verify ∘ Capture)
STALE PASS diff refresh (= Capture with delta input)

Heal and refresh are workflows over the three planes, not separate primitives.

Why competitors can’t bolt this on

Layer 1 / Layer 2 sources have to be captured at compile time. Cloud-first browser SDKs (Stagehand+Browserbase, Apify, Browserless) call the LLM at runtime against whatever the page currently shows — they have no captured baseline to verify against. Information-theoretically, they can detect that the LLM-extracted output changed; they cannot detect that the output became wrong. Detail in /compare/stagehand/.