{"name":"Letterprove","description":"Cryptographically attested proof of real product usage, published for evaluating agents.","signing":{"alg":"EdDSA","crv":"Ed25519","jwks_uri":"https://app.letterprove.com/.well-known/letterprove-jwks.json","canonicalization":"https://github.com/letterstory/Letterprove/blob/b028653e72168d2cd3ec3d4751d0fd67154d200b/src/lib/attest/canonical.ts","mode":"countersigned"},"verifier":"https://github.com/letterstory/Letterprove/blob/b028653e72168d2cd3ec3d4751d0fd67154d200b/scripts/verify.mjs","tiers":{"note":"Every attestation carries a `tier`. A valid signature proves only that this document is ours and unaltered — it says nothing about how good the underlying evidence is. The tier says that, and it is the claim. A signed tier-0 document asserts only that the vendor said so.","levels":[{"tier":0,"name":"vendor-asserted","means":"The vendor stated this. Nothing corroborates it — either no usage was observed, or the vendor has not proven control of the domain events are pinned to.","forgeable_by":"The vendor alone, trivially. Treat as a claim, not as evidence."},{"tier":1,"name":"script-observed","means":"Letterprove's script reported usage attributable to this company's email domain.","forgeable_by":"The vendor, with effort. The collector pins events to a verified origin, which a browser cannot forge — but a non-browser client can send whatever origin it likes."},{"tier":2,"name":"infrastructure-bound","means":"Observed usage carrying a Letterprove-side receipt timestamp and an origin pinned to a domain the vendor proved control of by DNS.","forgeable_by":"A determined vendor running a distributed spoofing rig. Volume and burst anomalies are scored against it; a slow, well-distributed rig is an accepted open gap."},{"tier":3,"name":"third-party confirmed","means":"An invoice that actually settled for this company, read directly from the vendor's own live-mode Stripe account, alongside observed usage. A subscription on its own does not qualify: it says what the vendor meant to bill, and a free one reaches `active` for nothing.","forgeable_by":"A vendor willing to pay themselves. Every condition is checked against a third party's ledger rather than the vendor's word, and money has to genuinely move through a processor in a Stripe-verified live account — but a vendor prepared to spend real money on a lie can still reach it. Read this as corroboration, not as immunity."},{"tier":4,"name":"customer counter-signed","means":"The customer reviewed this exact usage summary and approved it, at a link delivered to an address on their own domain. The vendor never held that link.","forgeable_by":"Nobody, without control of a mailbox at the customer's own domain. A vendor who registers a domain and invents a company on it controls both ends — fraud scoring, not this tier, is the backstop for that."}]},"proofs":[{"vendor":"lettertrace","url":"https://app.letterprove.com/proofs/lettertrace","aggregate":"https://app.letterprove.com/attest/lettertrace.json","aggregate_chain":"https://app.letterprove.com/attest/lettertrace/chain"},{"vendor":"letterstory","url":"https://app.letterprove.com/proofs/letterstory","aggregate":"https://app.letterprove.com/attest/letterstory.json","aggregate_chain":"https://app.letterprove.com/attest/letterstory/chain"}]}