# Change Check


A signed comparison of a retained original with current recorded observations, dates and gaps.

## At a glance

- **Attests:** The complete observation.record, including its signed source readings, dates, gaps and comparison or manifest. SHA-256 of observation.signed_payload is bound into certificate.attests. observation.signature_jcs covers the RFC 8785 canonical record.
- **Input:** baseline_cert_id, host (query parameters; input schema and checkout: https://scvd.store/menu/change_check?view=compact)
- **Output:** A signed comparison of a retained original with current recorded observations, dates and gaps Every artifact carries a cert_id and verifies free at https://scvd.store/api/verify/{cert_id}.
- **Cryptography:** ed25519 signature by this store's key, published at https://scvd.store/.well-known/scvd-signing-key and carried inside every 402
- **Verify:** GET https://scvd.store/api/verify/{cert_id} — free, no account, no rate limit, checkable offline with the published key
- **Price and fulfilment:** $0.005 USDC fixed, one-off; nothing here charges again by itself, ever — there is no mechanism that could; delivered instantly
- **Does not attest:** Live endpoint state, continuous coverage, successful future payment or delivery, or provider safety. No new observations does not mean no endpoint changes. Missing dates, different endpoints and different batteries cannot establish a comparable change.

## About this item

Give a host and the certificate ID of an earlier Spot Check with a retained original. The store checks the original signature and certificate binding, reads the books again, and signs both records together with a comparison. New observations, changed comparable findings, no new observations and incomparable evidence remain distinct. Both originals, observation dates and gaps travel with the result. The underlying history and freshness check stay free. Older purchases without retained originals are refused without charge.

- **id:** `change_check`
- **price:** $0.005 fixed, one-off; nothing here charges again by itself, ever — there is no mechanism that could
- **fulfillment:** delivered instantly
- **buy:** `GET https://scvd.store/api/buy/change_check?baseline_cert_id=<baseline_cert_id>&host=<host>` (USDC over x402 v2 on Base, Polygon, Arbitrum, World, Solana, or USDC over MPP (evm/charge) on Base for every shelf item, every publication page and the commission desk)
- **required inputs:** `baseline_cert_id`, `host` — fill the `<baseline_cert_id>`, `<host>` slots above before paying. The bare door `GET https://scvd.store/api/buy/change_check` quotes free and refuses the paid request without them; no money moves.
- **sample:** https://scvd.store/samples/change-check.json
- **does not prove:** Live endpoint state, continuous coverage, successful future payment or delivery, or provider safety. No new observations does not mean no endpoint changes. Missing dates, different endpoints and different batteries cannot establish a comparable change.

House rules: host is a bare hostname; baseline_cert_id must identify a retained spot check for that same host; no live request to the host; an unchanged record does not establish an unchanged endpoint; changed findings require dated observations of the same exact endpoint under the same named battery; no exact historical price comparison, continuous coverage or safety verdict.

> Half a cent for the two readings together, with what changed and what we still cannot see.