TxSentinel

TxSentinel is a deterministic pre-sign transaction policy firewall for autonomous agents and Agentic Wallets.

Before an agent signs an onchain action, TxSentinel evaluates the proposed transaction against user-defined spending limits, fees, slippage, recipients, approval scope, simulation results, and contract-verification requirements.

The live product provides two integration paths:

• A free preflight API that returns READY, REVIEW, or BLOCKED for testing and routing. It does not issue a formal decision, receipt, or authorization to execute the proposed transaction.

• A formal x402 policy API that returns an explainable ALLOW, HOLD, or DENY decision with a risk score, rule-level evidence, normalized policy snapshot, action digest, and deterministic SHA-256 receipt after payment settlement.

The paid API runs on X Layer Mainnet (eip155:196) and charges 0.01 USD₮0 per formal policy check through the official OKX x402 middleware. Buyers explicitly authorize each payment through OKX Wallet.

For optional onchain evidence, the canonical TxSentinelPolicyAnchor contract is deployed on X Layer Mainnet:

0xd3d07614461f98b365b0e609ca21718995cb4f98

The contract stores wallet-owned policy snapshots and deterministic receipt attestations. Its runtime bytecode has been verified against the reproducible reviewed artifact. The contract has no administrator, upgrade path, asset custody, token-transfer capability, or authority to execute user transactions.

TxSentinel never receives private keys, signs transactions, or broadcasts protected user transactions. Payment settlement, policy evaluation, evidence anchoring, and execution authority remain separate. The wallet is always the sole signing authority.

Live product:

https://txsentinel-okx.vercel.app

Source code:

https://github.com/FeeeeelixWong/txsentinel-okx

I built and deployed the complete TxSentinel MVP during the hackathon.

Completed:

• Live pre-sign policy console and public REST API

• Free preflight API with READY, REVIEW, and BLOCKED routing states

• Formal paid policy API with ALLOW, HOLD, and DENY decisions

• Deterministic policy evaluation with risk scores, rule-level evidence, action digests, and SHA-256 receipts

• Clear separation between free non-binding preflight results and formal paid policy decisions

• Official OKX x402 server integration using the OKX Express, Core, and EVM packages

• Production payment migration to X Layer Mainnet (eip155:196)

• 0.01 USD₮0 pay-per-check service on X Layer Mainnet

• Browser payment workflow using OKX Wallet, including live quote loading, network verification, balance checking, EIP-3009 authorization, settlement, and receipt rendering

• Prepayment validation so invalid formal requests fail before payment is requested

• Canonical TxSentinelPolicyAnchor contract deployed on X Layer Mainnet

• Mainnet contract address:

0xd3d07614461f98b365b0e609ca21718995cb4f98

• Mainnet deployment transaction:

0x4db42ec3853b346318b3a5d37cf9d71dcbeefe5e0d98cbf0a494dbc794175215

• Mainnet contract runtime bytecode verified against the reproducible reviewed artifact

• Mainnet Onchain console for wallet-owned policy registration and deterministic receipt anchoring

• Non-custodial smart-contract design with no administrator, upgrade path, external execution call, or asset-transfer authority

• Historical X Layer Testnet x402 settlement retained as reproducible integration evidence

• 31 automated tests covering policy behavior, HTTP APIs, official x402 middleware, smart-contract security invariants, and deployment metadata

• Production deployment:

https://txsentinel-okx.vercel.app

• Public GitHub repository with reproducible contract artifacts, security review, deployment evidence, architecture documentation, and bilingual documentation

• TxSentinel v1.2.0 GitHub Release published with the X Layer Mainnet PolicyAnchor deployment

• OKX ASP Agent #6828 configured for the production mainnet payment service and submitted for platform review

TxSentinel is bootstrapped and self-funded. I have not raised external equity, institutional, or token funding for this project.

I independently cover the current development, infrastructure, testing, and deployment costs. The initial business model is usage-based API revenue through x402 pay-per-policy-check access, with future enterprise plans for agent wallet platforms and automation teams.