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Validity Transaction Builder
x402
Validity Transaction Builder is a paid API for AI agents from 402.com.tr, paid per call via x402, $0.01/call, status unknown (last checked 2026-10-14).
Wraps a signed Base transaction in a Cobalt validity envelope so Base holds it dormant until specified on-chain conditions are met, then returns the base_sendRawTransactionValidity payload ready to broadcast.
Price / call$0.01
Success—
StatusUnknown
How this service works
Wrap ANY signed Base transaction (transfer, approve, contract call) in a Cobalt validity transaction: Base holds it dormant until your conditions hold, then includes it — a good-till-block/conditional order, no limit-order contract, nobody holding it. We validate the predicates and return the base_sendRawTransactionValidity request; we never touch funds or keys. Conditions: beforeBlock, fromBlock, flashblockIndex, minNativeBalanceWei, or a storage predicate for price. One required.
Output
Returns the constructed base_sendRawTransactionValidity JSON-RPC request object ready to submit to a Base node or bundler. The response includes the validity-wrapped transaction with all validated predicates (block range, balance floor, flashblock index, storage condition) encoded. No keys or funds are touched — the service only builds and validates the envelope.
Example use cases
Deadline-gated token transfer
“I have a signed Base ETH transfer I want to send, but only if it gets included before block 22600000 — wrap it in a validity transaction with that deadline and return the payload I can broadcast.”
Balance-floor conditional approve
“Wrap my signed ERC-20 approve transaction so it only executes if my wallet still holds at least 500000000000000000 wei (0.5 ETH) — I don't want it going through if I've already spent down my balance.”
Storage-price-gated contract call
“I have a signed swap call and I only want it to execute when the price storage slot 0x0 on the Uniswap pool 0xAbC... reads less than 0x1BC16D674EC80000 — build me the validity transaction with that storage predicate.”
Technical details
Endpoint
GEThttps://402.com.tr/api/x402/validity-build?utm_source=zero.xyzWhen to prefer
Choose this endpoint when you need to attach expiry, block-range, balance-floor, flashblock, or on-chain storage conditions to an already-signed Base transaction without deploying a limit-order smart contract or handing funds/keys to a third party. It is the right tool for good-till-block orders, conditional transfers, and price-gated approvals on Base L2 using the native Cobalt validity mechanism rather than a wrapper contract.
Side effects
- No condition provided — at least one predicate (beforeBlock, fromBlock, flashblockIndex, minNativeBalanceWei, or storage slot) is required
- Invalid or malformed signedTx hex — returns error if transaction cannot be deserialized
- Storage predicate fields incomplete — storageAddress and storageSlot required when using storage conditions
- Invalid operator value for storageOp or flashblockIndexOp — must be one of < <= = != > >=
- Block numbers provided as non-numeric strings — causes predicate validation failure
- Payment not fulfilled — $0.01 USDC x402 payment must accompany the request
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Tags
x402
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