FactStamp

FactStamp

Paid verification for agents, and a public record of every paid answer. Each call returns a cited, dated finding with a signed receipt you can verify offline, without asking us. Each settled call is written into a public log, and each day's root is stamped onto the Base blockchain whenever that day held a payment from someone other than us. When a check has to stay confidential there is a private option: a flat US$25 on top of the call price seals the request, so the world can see that a call happened and prove it later, but never learn what was asked. No model sits in the verdict path, and unknown is a first-class answer.

Live service: https://agents.factstamp.dev

What this repository is

The published machine interface of the FactStamp service, mirrored here so it can be read, diffed and cited without a wallet. Each row names the live route the copy came from, so any file here can be checked against the service in one request:

File	What it is	Live source
openapi.json	The OpenAPI 3.1 description of every route.	https://agents.factstamp.dev/openapi.json
llms.txt	The plain-language map of the service: what each tool costs, what it returns, what it refuses to claim.	https://agents.factstamp.dev/llms.txt
coverage.json	Which registers are read, per jurisdiction, section by section, with the price of each door.	https://agents.factstamp.dev/coverage.json
server.json	The MCP registry manifest — the entry submitted to the official registry, not a route the service serves.	https://agents.factstamp.dev/.well-known/mcp.json (the live descriptor)

These are dated snapshots, not a live feed. Coverage and prices move as registers change, so a copy here can lag the service. When the two disagree, the live route wins — fetch it and believe that, not this. The files exist so a person or an agent without a wallet can read the interface, and so a reader can cite exactly what was published on a given day.

The service's private source is not published here.

Routes

Route	Purpose	Access
/mcp	MCP endpoint — the tool surface agents call.	—
/health	Service status: name, network, judge and registry versions.	open
/openapi.json	Machine description of every route.	open
/llms.txt	The service explained for readers.	open
/coverage.json	Per-jurisdiction coverage and prices.	open
/samples	Example answers, so you can see the shape before paying.	open
/ledger/root	The public record: today's root, the last 30 daily roots, and each day's verdict.	open
/ledger/zero-knowledge	The private-request option: what it is, what it publishes, what it costs.	open

Paid routes include /citation, /package, /check, /entity, /entity-file, /bulk, /document, /watch, /watch/portfolio, and /verify for receipt checking. Prices are published, per call, in the files above rather than in prose here.

Published prices at the time of writing

Taken from /health and /llms.txt as served:

• figure door — US$0.05
• entity door — US$0.10 to US$0.25, set by the depth of the country you ask about: US$0.10 for a country publishing 1–4 verifiable items, US$0.15 for 5–6, US$0.20 for 7–9, US$0.25 for Australia's fifteen. The quote is shown in the payment challenge, before any money moves, and a country whose register cannot answer today is not sold at all — it is refused with no price rather than charged for an "I don't know".
• entity file — US$0.438119 (33p in the UK, at the dated rate carried on the answer and the receipt)
• citation — US$0.02, package lookup — US$0.02
• standing work: watch US$0.50, whole document in one call US$0.25, bulk at a flat US$0.12
• company packages: US$2.00 and US$10.00, one-time, from the human page at /company

If a number here ever disagrees with llms.txt or openapi.json as served, the served file wins.

Receipts

Every paid answer carries a receipt signed with Ed25519 over the exact findings and the file's hash, so a third party can verify it offline against the published issuer and key document — no call back to us, and no trust in our uptime. The key document at /.well-known/factstamp-issuer.json states exactly which bytes the key identifier is derived from and carries a worked example, so the derivation can be reproduced in any hash tool. A receipt proves that FactStamp said this, on this date. It does not prove that the register itself is right, and nothing in this service claims it does.

The public record: the ledger, and what is stamped on Base

Every settled paid call, over HTTP and over MCP alike, appends one entry to a public log. The log is an RFC 6962 Merkle tree; each UTC day's log reduces to a single root, published at /ledger/root along with the last thirty days.

A day's root is written to the Base blockchain — one small data-only transaction, magic 0x46535401 followed by the 32-byte root — only when that day held at least one settlement paid by someone other than us. Our own test payments never anchor a day. The rule exists so that an anchor means something: a day is stamped because a stranger paid, not because we were busy.

Days already written (verifiable on Base, chain id 8453):

Day	Transaction
2026-10-23	0x3bd942ae61c053aa7218ebfe44c25db2d9726412a67ec75073267cfb376d38f3
2026-10-25	0xa80b18f7d829fe535d86a700daa98f7f69f183877f158f1f0b2094dd2a94138f

A day that held no outside payment is published with the verdict that says so, rather than being quietly left blank. The honest limit: an anchor proves the root was committed publicly on the day the transaction landed, not on the day of the payment — the payment itself is already a public record, because it is a transfer on the same chain. The anchor adds our side of the story: that the answers we gave were fixed before anyone asked to see them.

Private requests: the sealed-entry option

By default a paid call's entry is published in full — the door, the price, the verdict, and the fact that the call happened. For a caller who needs the call itself to stay confidential there is a zero_knowledge option, declared on the request.

• Price: US$25.00 in addition to the call's own price. A US$0.10 entity check declared private costs US$25.10. The payment challenge quotes the total before anything is paid.
• What is published: an entry_id, the day, the price, the scheme (salted_commitment_v1) and the network. Nothing else.
• What is sealed: the question, the answer and the verdict. The entry is committed to with a salted hash, so its existence and its position in the log are public while its contents are not.
• What that buys: you can prove later that a specific call happened on a specific day — by revealing the salt to whoever needs it — without ever having published what you asked.

The private option is documented at /ledger/zero-knowledge, with its own root at /ledger/zero-knowledge/root and its entries at /ledger/zero-knowledge/entry/{entry_id}. It is an option on the paid doors, not a separate service.

What this service is not

• Not a KYB provider, and not a substitute for one. It does not perform customer due diligence on anyone's behalf.
• Not complete by assertion. Any register we did not consult is named on the answer as not consulted. A register we could not read returns unknown, never not found.
• Not a fetcher of records you can already get at no cost. You are paying for the citation, the check and the receipt, not for the register's own data.

Issues

Corrections about a claim we make are welcome as issues here. If we have said something about a company, a number or a register that is wrong, that is the fastest way to tell us.