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What is
Acceptance Predicate?
An ErgoScript condition embedded in a Note's spending logic that must be satisfied at redemption — enabling trustless payment-for-task without off-chain oracles.
An acceptance predicate is an ErgoScript expression in a Note's spending script (or receiver's box script) that encodes conditions for valid redemption. Example: 'Accept this payment only if the blake2b256 hash of the task output matches TASK_HASH, and the current block height is less than DEADLINE.' Acceptance predicates move payment conditions on-chain, eliminating the need for off-chain dispute resolution, oracle trust, or centralized escrow. This is a key primitive for autonomous agent commerce — the agent pays with a Note; the receiver's script enforces the business logic.
Key Points
- Embedded in the Note spending script or receiver's box script
- Evaluated at redemption time — no off-chain oracle needed
- Can reference: task hash, block height deadline, credential proof, minimum value
- Written in ErgoScript — sigma-protocol based, formally verifiable
- Enables trustless payment-for-task: 'accept only if work is proven'
- Composable with Sigma protocols for zero-knowledge task proofs
Use Cases
1
API provider: 'accept payment only if request hash matches delivered response'
2
Compute job: 'accept payment only if proof-of-work output hash is correct'
3
Data feed: 'accept payment only before block 1,500,000 deadline'
4
Multi-step pipeline: 'accept only if all upstream task hashes are present'
Technical Details
Example ErgoScript acceptance predicate: `sigmaProp(blake2b256(getVar[Coll[Byte]](0).get) == TASK_HASH && HEIGHT < DEADLINE && noteValue >= PRICE)`. The context variable `getVar(0)` is provided by the redeemer at spending time — they submit the task output preimage, and the script verifies the hash. This makes the payment atomically conditional on task delivery.
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