Marketplace Listing and Order Schema Standard

The Marketplace Listing and Order Schema Standard addresses a critical fragmentation point in the Bitcoin Ordinals and Runes ecosystem: the lack of a unified, trustless mechanism for creating and sharing orders across different marketplaces. Currently, each marketplace operates its own proprietary order book, forcing users to trust the platform's backend and fragmenting liquidity. This proposed standard defines a common schema for constructing off-chain listing and bid messages using PSBTs, allowing any compliant marketplace, wallet, or aggregator to create, share, and fulfill orders without requiring a central intermediary to hold assets or manage a private database.

At its core, the standard leverages the PSBT format (BIP-174) to encode the terms of a trade—such as the specific Ordinal inscription or Rune being offered, the requested price in Bitcoin, and the seller's signature—into a portable, partially signed transaction. A seller can create a signed listing PSBT that authorizes the transfer of their asset upon receipt of the specified payment, while a buyer can create a signed bid PSBT committing funds for a desired asset. A third party, such as a marketplace or an atomic swap coordinator, can then match these complementary PSBTs and finalize the transaction on-chain. This architecture removes the need for marketplaces to take custody of user assets for listing purposes, significantly reducing counterparty risk and the attack surface for exchange hacks.

For builders and operators, the operational impact is substantial. Marketplace developers must implement PSBT construction and parsing logic that correctly handles the unique constraints of Ordinals (inscription envelopes, satpoint selection) and Runes (UTXO-based balances, cenotaph risks). A flawed implementation could lead to race conditions where an asset is double-sold, or to cenotaph triggers that destroy rune balances. Indexer operators need to ensure their APIs can validate the state of assets referenced in a PSBT order. Chainscore Labs can provide a critical audit of this integration layer, reviewing PSBT construction logic, order-matching engines, and UTXO selection algorithms to prevent asset-loss vulnerabilities and ensure cross-platform compatibility.

The Marketplace Listing and Order Schema Standard defines a mechanism for creating off-chain order books for Bitcoin-native assets, including Ordinals and Runes, using Partially Signed Bitcoin Transactions (PSBTs). A seller constructs a PSBT that spends a specific UTXO containing an inscription or rune balance, setting the desired output and price, but without signing the input. This unsigned PSBT represents a verifiable listing that can be broadcast across marketplaces. A buyer can then complete the transaction by adding their own inputs to fund the purchase, signing their portion, and finalizing the PSBT for broadcast to the Bitcoin network. This schema shifts the trust model from a centralized marketplace escrow to the cryptographic validity of the Bitcoin transaction itself.

Operationally, this standard requires precise PSBT construction to prevent asset loss. A listing PSBT must correctly identify the asset-bearing UTXO, set appropriate outputs for the buyer and any marketplace fee, and crucially, leave the seller's input unsigned. The PSBT_GLOBAL_UNSIGNED_TX field contains the skeleton transaction, while PSBT_IN_SELLER roles and proprietary key-value pairs may be used to communicate listing metadata. The primary risk is a race condition where a seller signs a listing PSBT, allowing a malicious relayer to broadcast it without the buyer's payment, effectively stealing the asset. Therefore, the standard mandates that the seller's signature is only applied by the buyer's wallet software as the final step of a valid acceptance, or that the listing PSBT is constructed in a way that is invalid until the buyer's inputs are added.

For marketplace developers and shared-liquidity infrastructure, this schema introduces a new class of off-chain state management. Indexers must be capable of parsing these PSBTs to display active listings, and wallet software must implement robust PSBT finalization logic that validates the entire transaction graph before signing. The cenotaph model of Runes adds a critical dimension: a malformed final transaction can destroy all input runes. Chainscore Labs can audit the PSBT construction and order-matching logic in marketplace and wallet implementations to verify that race conditions are impossible, fee outputs are correctly structured, and that Runes transfers are constructed with valid edicts to prevent catastrophic cenotaph-triggered loss.