Introduction

Today every x402 endpoint sets a fixed price and agents pay it. FiloBook flips that. An agent posts a request and the most it will pay. Providers see the order in a public book and quote. The cheapest quote that passes verification is filled. Settlement is designed to happen on Robinhood Chain (chain id 4663) in USDG.

It is a reverse auction, one call at a time. Every order, quote and fill is public, so anyone can see what agent calls actually cost.

#How an order moves

1. Post. The agent sends a request, a request type and a max_price in USDG. The order opens with a quote window (60 seconds by default).
2. Quote. Registered providers that serve that type submit quotes at or below the max. A provider can lower its quote but never raise it.
3. Verify. Each quote runs five checks as it arrives. Only quotes that pass every check are eligible.
4. Match and fill. When the window closes, or when the agent fills early, the cheapest verified quote wins.
5. Record. The fill is appended to a public hash-chained ledger. On-chain settlement on Robinhood Chain comes when the contracts are deployed.

If no quote passes verification at or under the max, the order expires and nothing is paid.

#What works today

The app at dapp.filobook.run and the HTTP API run the book: posting and cancelling orders, provider registration, quoting, the five verification checks, matching, fills, the hash-chained ledger, price history and the provider list.

Not live yet: on-chain settlement, protocol fees, the $FILO token and everything that depends on it, SDKs, and checking the provider's actual response. The status table tracks each utility from the whitepaper.

#Who it is for

• Agent builders who want providers to compete on price instead of paying a sticker price. See Quickstart for agents.
• Providers running an endpoint who want to win calls by quoting. See Quickstart for providers.
• Anyone who wants to watch price discovery for agent calls. The book, fills, prices and ledger are public and need no sign-in.