Magneta Contract Risk (x402)

A small production-oriented service that sells an on-chain smart-contract risk report to AI agents, paid per call with x402 micropayments (USDC, EIP-3009 exact scheme). One express process, two paid surfaces:

Surface	Route	Price
HTTP	GET /v1/risk/:chainId/:address	$0.02
MCP (Streamable HTTP, stateless)	POST /mcp, tool contract_risk_summary(chainId, address)	$0.02
MCP	tool supported_chains	free
Health	GET /health	free

Both paid surfaces call the same analyzeContract(chainId, address) in src/risk/analyze.ts. The analysis is deterministic and uses public data only (RPC, Blockscout, Sourcify, a local aderyn binary). No LLM, no API key for analysis. Unknown chain or malformed address returns 400 before any payment is requested. If the analysis itself fails (not a contract, upstream error, timeout) the response is an error status and the buyer is not charged (x402 only settles successful responses).

Supported chains (v1, src/chains.ts): Base 8453, Base Sepolia 84532, Ethereum 1, Arbitrum One 42161. Override RPCs with RPC_URL_<chainId>.

Report

{ chainId, address, analyzedAt, isContract, bytecodeSize, proxy, erc20, opcodes, selectors: { found },
  blockscout, sourcify?, aderyn, score, level, flags, notes }

• proxy: { type, implementation, admin? } from EIP-1967 (implementation/admin/beacon), legacy zeppelinos slot, EIP-1822, EIP-1167 clones, or Blockscout's detection. The implementation bytecode is analysed too.
• erc20: name, symbol, decimals, totalSupply, owner() (and whether it is the zero address), paused(). Each probe is individually try/catch.
• opcodes: SELFDESTRUCT / DELEGATECALL presence from a real opcode walk that skips PUSH data (no substring matching).
• selectors.found: risky signatures (mint, pause, blacklist, fee/tax setters, upgrade, ownership...) whose 4-byte selector appears as a PUSH4 in the bytecode. Heuristic: presence is not proof of reachability (also stated in notes).
• blockscout / sourcify: verification status, compiler, contract name, creator and creation tx. Blockscout has a 5 s timeout; on failure blockscout: { available: false }. Sourcify is only queried as a fallback when Blockscout is unreachable or reports "unverified". For proxies, the implementation's verification is what counts.
• aderyn: when verified Solidity source is available, sources are written to a temp dir (sanitised paths) and aderyn runs with a 15 s timeout: { ran, counts: { high, low }, top: [{ title, severity, instances }] }, else { ran: false, reason }. It never fails the request.
• Total budget: hard deadline 24 s per analysis. Results are cached in memory for 10 minutes per chainId+address (the payment still happens on every call).

Score rubric (src/risk/score.ts)

Score 0..100, higher = riskier, additive, capped at 100.

Points	Condition
+25	logic contract source not verified (Blockscout, then Sourcify)
+0 (flagged)	verification unknown because every provider was unreachable
+15	proxy / upgradeable
+10	owner() exists and is not the zero address
+15	mint selector
+15	blacklist / bot-list selector
+10	fee / tax / limit / trading-switch setters
+5 (+5 if currently paused)	pause selector
+10	SELFDESTRUCT opcode
+5 each, max +20	aderyn high-severity findings

Level: 0-24 low, 25-49 medium, 50-74 high, 75-100 critical. A non-contract address is an error, not a score. The score is a triage signal, not an audit.

Supported chains

Mainnets: Ethereum (1), OP Mainnet (10), BNB Smart Chain (56), Gnosis (100), Unichain (130), Polygon (137), Sonic (146), World Chain (480), Mantle (5000), Base (8453), Arbitrum One (42161), Celo (42220), Avalanche C-Chain (43114), Linea (59144), Blast (81457), Scroll (534352). Testnets: Base Sepolia (84532), Sepolia (11155111), OP Sepolia (11155420), Arbitrum Sepolia (421614). Chains without a Blockscout instance (BNB, Sonic, Mantle, Avalanche) rely on Sourcify for verified sources. zkSync Era is excluded on purpose: EraVM bytecode defeats the opcode and selector heuristics. Compiler remappings from Blockscout or Sourcify are written to remappings.txt so aderyn can resolve @openzeppelin/...-style imports.

Run

pnpm install --ignore-scripts
cp .env.example .env.local      # fill PAY_TO, X402_NETWORK, FACILITATOR_URL (+ CDP keys if cdp)
pnpm dev                        # tsx, or: pnpm build && pnpm start
pnpm type-check && pnpm test    # unit tests, no network
pnpm analyze 84532 0x036CbD53842c5426634e7929541eC2318f3dCF7e   # free local run, prints the report

Buying (needs a funded buyer key, spend cap $0.05; never put this key on the server):

BUYER_PRIVATE_KEY=0x... pnpm buy-once        # HTTP; prints the report and the PAYMENT-RESPONSE tx hash
BUYER_PRIVATE_KEY=0x... pnpm buy-once-mcp    # same through the MCP tool

Environment

• PUBLIC_URL (https, no trailing slash): advertised as the MCP resource URL for Bazaar discovery. Behind a reverse proxy the server trusts the loopback proxy (trust proxy = loopback) so HTTP resource URLs are advertised as https://; without that, the facilitator rejects discovery with "resource must start with https://".

Var	Meaning
PORT	listening port (default 3011)
PAY_TO	receiving address (required)
X402_NETWORK	CAIP-2 network, default eip155:84532 (Base Sepolia); production: eip155:8453
FACILITATOR_URL	cdp (Coinbase CDP facilitator, needs CDP_API_KEY_ID + CDP_API_KEY_SECRET) or an HTTP facilitator URL such as https://x402.org/facilitator (testnet)
ADERYN_BIN	aderyn 0.6.8 binary, default /home/dominique/bin/aderyn
RPC_URL_<chainId>	optional RPC override per chain
BUYER_PRIVATE_KEY, TARGET_URL, MCP_URL, CHAIN_ID, ADDRESS	buyer scripts only

Deploy (systemd + Caddy)

pnpm install --ignore-scripts && pnpm build
rsync -a --exclude node_modules ./ server:/srv/magneta/risk-x402/    # then pnpm install --prod --ignore-scripts there
sudo cp deploy/magneta-risk-x402.service /etc/systemd/system/ && sudo systemctl enable --now magneta-risk-x402
# add deploy/Caddyfile.snippet to the Caddyfile (vhost x402.magneta.finance -> 127.0.0.1:3011), reload Caddy

The unit reads /srv/magneta/risk-x402/.env.local. For mainnet set X402_NETWORK=eip155:8453 and FACILITATOR_URL=cdp. Aderyn needs its solc download/cache available to the service user (HOME writable).

Bazaar discovery

Both paid surfaces declare x402 Bazaar discovery metadata with declareDiscoveryExtension from @x402/extensions/bazaar (HTTP route with path-parameter schema and output example; MCP tool with input schema), and the bazaarResourceServerExtension is registered on the resource server. The metadata appears in the PAYMENT-REQUIRED header (extensions.bazaar). Actual cataloguing depends on the facilitator: it indexes resources when it settles a payment, so the listing appears only after the first real paid call through a Bazaar-enabled facilitator (CDP). The public x402.org testnet facilitator is not expected to list it.

Production status (2026-10-16)

Live at https://x402.magneta.finance on Base mainnet (eip155:8453), Coinbase CDP facilitator, $0.02 per call, listed in the x402 Bazaar (route /v1/risk/:chainId/:address). Buyers need USDC on Base and no ETH. The facilitator rejects payments where the payer equals payTo (self_send_not_allowed).