Sentinel — an autonomous audit agent for Mantle

The Turing Test Hackathon 2026 · Track: AI DevTools

▶ Try it live (no install): https://sentinel-audit.surge.sh — paste any Solidity contract and run the exact 14-detector audit engine in your browser.

Sentinel is an AI agent that audits Solidity smart contracts for security bugs and Mantle/L2-specific gas waste — and it is itself an on-chain economic actor: it holds an ERC-8004 agent identity and charges per audit via x402 micropayments. Point it at a contract, it pays-walls the audit behind a stablecoin micropayment, returns a structured report, and records the audit on Mantle so the agent builds a verifiable on-chain track record.

Plain version: it's a robot security reviewer for blockchain code. You hand it a contract, it finds the dangerous mistakes and the parts that waste money to run, and it takes a tiny automatic payment for the job — no invoices, no accounts, just code paying code.

Why this fits the "AI Awakening" theme

The hackathon benchmarks autonomous agents that act on-chain. Most agents spend money (they call paid APIs). Sentinel earns it: a self-supporting agent that sells a real service (audits), gets paid trustlessly (x402), and accrues reputation under a portable identity (ERC-8004). That is an agent with an actual economy around it, not a chatbot with a wallet bolted on.

Status (honest)

Layer	State
Audit engine (14 detectors, AST-based, never crashes on bad input)	✅ working, tested
CLI (sentinel Contract.sol [--json], CI-usable exit codes)	✅ working
ERC-8004 Identity + Validation registries (Foundry, 7 tests)	✅ working, tested
x402 pay-per-audit HTTP gateway (402 challenge → verify → settle)	✅ working, tested
On-chain audit attestations (report hash + risk score per paid audit)	✅ working, tested
End-to-end loop proven on a live EVM (Anvil, 4 e2e tests)	✅ working, tested
Registries deployed to Mantle Sepolia (see contracts/DEPLOY.md)	✅ live on-chain
Demo video + DoraHacks BUIDL submission	⏳ next

Live on Mantle Sepolia (chain 5003): IdentityRegistry 0x8F18f53a7ED086FFe409933668b2F3c48d26CbF4 · ValidationRegistry 0x6925CDFb19606C165d1ce4bCA16895a9a9Ac3507 · Sentinel agentId 1 (sentinel.audit). View on explorer.

Real on-chain audit receipt (not a simulation): Sentinel audited a vulnerable Vault.sol (5 findings, risk 57/100) and anchored the report hash to the live Validation Registry — record #0, agent #1: tx 0x0c6ccdba…. Reproduce: PRIVATE_KEY=0x… npm run attest:live (writes media/onchain-attestation.json).

The whole earning loop — buyer pays via x402 → agent audits → report anchored on-chain → USDC settles — runs and is asserted end-to-end against a real EVM. npx tsx scripts/demo.ts plays it start to finish (this is the demo-video script).

The audit engine (live now)

AST analysis via @solidity-parser/parser. Every detector is sandboxed: one failing detector can never abort the audit, and malformed Solidity returns a clean parser error instead of crashing. Findings are sorted by severity and the contract gets a 0–100 security score.

Detectors

Security:

• SEC-001 authorization via tx.origin
• SEC-002 unchecked return of low-level .call/.send
• SEC-003 use of selfdestruct
• SEC-004 delegatecall to a runtime-controlled target
• SEC-005 block properties used as randomness/critical source
• SEC-006 externally callable state-changing function with no access control
• SEC-007 reentrancy (state written after an external call, no guard)

Gas:

• GAS-001 require() with revert string → custom errors
• GAS-002 array .length read inside loop condition → cache it
• GAS-003 post-increment i++ loop counter → ++i
• GAS-004 reference-type param in public fn copied to memory → external + calldata
• GAS-005 literal-initialised state var that could be constant/immutable

Mantle / L2-aware:

• MNT-001 block.number used for time (unreliable cadence on L2s)
• MNT-002 native transfer via .transfer()/.send() (brittle 2300-gas stipend on L2)

CLI usage

npm install
npm run build
node dist/cli/index.js path/to/Contract.sol        # human report
node dist/cli/index.js path/to/Contract.sol --json  # machine report
cat Contract.sol | node dist/cli/index.js            # stdin

Exit code is non-zero when any HIGH-severity issue is found, so it drops straight into CI.

The agent: x402 + ERC-8004 (live now)

Sentinel runs as an HTTP agent (src/server/) that sells audits:

GET  /.well-known/agent.json   ERC-8004 AgentCard: identity, capabilities, price
POST /audit                    x402-paywalled; { source } -> report + on-chain attestation

The payment flow follows the x402 "exact" scheme:

1. Unpaid POST /audit returns HTTP 402 with the payment requirements (accepts[]: scheme, amount, asset, payTo, network).
2. The buyer signs an EIP-3009 TransferWithAuthorization (a gasless USDC authorization) and resends it as a base64 X-PAYMENT header.
3. Sentinel verifies the signature, runs the audit, writes the report hash + risk score to the ERC-8004 Validation Registry, and only then settles the payment on-chain. The buyer pays for a delivered, anchored result — never for a 402, never for a failed settlement.

Payment verification/settlement is pluggable (src/x402/verify.ts):

• LocalVerifier — verifies the EIP-712 signature offline and settles via transferWithAuthorization using a relayer wallet. Self-contained: no external facilitator, works against any EVM you control (Anvil, Mantle, …).
• FacilitatorVerifier — delegates verify/settle to a hosted x402 facilitator.

On-chain contracts (contracts/)

• IdentityRegistry — minimal ERC-8004: each agent gets a unique on-chain id resolvable by domain/address. Sentinel registers itself here.
• ValidationRegistry — proof-of-task-completion: every paid audit records (auditorAgentId, subjectHash, reportHash, riskScore). A buyer can later verify() that the report they hold is exactly what was anchored, and read the agent's full audit track record.

# run the live agent against a local chain
PATH=$HOME/.foundry/bin:$PATH npx tsx scripts/demo.ts

Test

npm test                                  # vitest: analyzer + HTTP gateway + e2e
PATH=$HOME/.foundry/bin:$PATH forge test  # Foundry: registry contracts

• test/analyzer.test.ts — 14 detectors fire on the vulnerable fixture; clean ≥ 90.
• test/server.test.ts — 402 challenge, malformed/invalid rejection, paid flow, and "settlement failure ⇒ no free audit".
• test/e2e.chain.test.ts — boots Anvil, deploys everything, registers the agent, funds a buyer, drives a real signed x402 payment through the live app, and asserts the USDC moved, the report verifies on-chain, and replays are rejected.

Roadmap to submission (deadline 2026-06-15)

1. ✅ ERC-8004 registries + agent registration (deploy script ready).
2. ✅ x402 pay-per-audit gateway in front of the audit API.
3. ✅ On-chain attestation of each report; full loop proven on a live EVM.
4. ⏳ Deploy to Mantle Sepolia (gas-blocked — contracts/DEPLOY.md).
5. ⏳ 2–3 min demo video (driven by scripts/demo.ts); submit BUIDL on DoraHacks.

License

MIT