Public evidence

finance.vat

Machine-checked verification for calculation version 1.3.0 · tier engine_tested

Open calculator API Capability Download JSON MCP Review policy

Verification

4/4 calculation tests · Production surface contract 4/4

Golden tests 4 / 4
Boundary tests 0 / 0
Property tests 0 / 0
Production surface contract 4 / 4
Engine tested Yes
Source checked Yes
Artifact integrity PASS
Production attestation Embedded snapshot: STALE · Last attested schema matched 1.3.0 snapshot / local build · Semantic contract ✓ · Last attestation PASS · current evidence changed · re-attestation required · Public/cache ✓ · Origin ✓ · Live production status PASS (0 stale; 164 CURRENT) @ 2026-09-16T06:44:24.909Z
Semantic contract PASS
Evidence attested at 2026-09-16T06:44:24.203Z
Last production check 2026-09-16T06:44:24.203Z
Public / cache PASS
Origin PASS
Supplemental domain review Not performed
Named expert review Not performed

release artifacts aligned PASS
schema valid input executes PASS
engine success output validates schema PASS
schema rejects incomplete input PASS

Fingerprint sha256:2fc504ba9fc5e0e81de0f070ed4f9744d1b8c0e27c759598e010039b49c65133

Input schema sha256:5d66b6d1b6cda55f6b1f566d99df4c4843973fa2f4576b9ec293d10517ff28da · Output schema sha256:802f8ae25f1a9dd159c6c25296a4f6734b5416995ed2de46bfc0eba5aa50e912 · Build-time SHA-256 digests prove published artifacts agree with each other (release_integrity.scope=workspace). Production attestation GETs canonical URLs twice (public/cached view and origin), including Capability HTML, via npm run attest:production --write (published at /.well-known/calculatorx-production-attestation.json) and fails if the public Capability page advertises a different calculation_version. This is artifact consistency, not an independent immutable release log.

Build & scope

Engine identity and declared limitations.

Tool: vat
Engine: vat
Engine build: 2026-09-15
Evidence core: 2026-09-15T06:31:46.555Z
Rendered: 2026-09-16T22:03:43.768Z
Last reviewed: —

Assumptions

Single flat rate on the entered amount
No multi-rate baskets or input-tax credits modeled

Limitations

Single flat rate on the entered amount
No multi-rate baskets, exemptions, or input-tax credits
GST page is an SEO entry of this capability — same engine, GST labeling

Sources

Standards and references supporting this tool specification. Methods are listed separately — they are algorithms, not bibliographic sources.

OECD International VAT/GST Guidelines — value-added tax as a consumption tax on the value added
HMRC VAT guide (UK, conceptual) — gross = net × (1 + rate); net = gross / (1 + rate)

Published checks

Golden, boundary, and property cases included in this evidence build.

ID	Kind	Status	Detail
`add-100-20`	golden	pass	Expected net=100 · tax=20 · gross=120 · Actual net=100 · tax=20 · gross=120
`remove-120-20`	golden	pass	Expected net=100 · tax=20 · gross=120 · Actual net=100 · tax=20 · gross=120
`add-1000-5`	golden	pass	Expected gross=1050 · tax=50 · Actual net=1000 · tax=50 · gross=1050
`remove-1000-20`	golden	pass	Expected net=833.3333 · tax=166.6667 · Actual net=833.3333333333334 · tax=166.66666666666663 · gross=1000