Solidity heuristic pattern scan

Deterministic static pattern scan of Solidity smart-contract source text - a fixed ruleset flagging tx.origin authentication, delegatecall, selfdestruct, unchecked low-level calls, unchecked .send(), floating pragmas, block-timestamp dependence, weak block-derived randomness, value-call reentrancy surface, inline assembly, ecrecover, and missing SPDX headers. Send POST /api/solidity-scan with the required field source and pay $0.01 per call over x402 or MPP, or call it free by solving a proof-of-work challenge. It returns a JSON object with lines, findings, summary and disclaimer.

Returns line-anchored findings with severities. This is a heuristic pattern check for triage - it is NOT a compiler, NOT a formal audit, and uses no AI. Pair with /api/contract-source to scan any verified contract.

Category: Crypto & onchain data · Tags: crypto solidity smart-contract security audit auditor static-analysis contract

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Parameters

Example request

curl -i -X POST https://agent402.tools/api/solidity-scan \
  -H "Content-Type: application/json" \
  -d '{"source":"pragma solidity ^0.8.0;\ncontract Wallet {\n  function drain(address payable to) external {\n    require(tx.origin == msg.sender);\n    to.call{value: address(this).balance}(\"\");\n  }\n}"}'

Without payment this returns HTTP 402 Payment Required with the exact price for solidity-scan; any x402 v2 or MPP client pays it and retries.

Example response

{
  "lines": 7,
  "findings": [
    {
      "rule": "tx-origin",
      "severity": "high",
      "line": 4,
      "snippet": "require(tx.origin == msg.sender);",
      "message": "tx.origin used - authentication via tx.origin is phishable; use msg.sender."
    }
  ],
  "summary": {
    "high": 2,
    "medium": 1,
    "low": 1,
    "info": 1
  },
  "disclaimer": "Deterministic heuristic pattern check - not a compiler, not an audit."
}

From an MCP client

catalog.call {
  "slug": "solidity-scan",
  "params": {
    "source": "pragma solidity ^0.8.0;\ncontract Wallet {\n  function drain(address payable to) external {\n    require(tx.origin == msg.sender);\n    to.call{value: address(this).balance}(\"\");\n  }\n}"
  }
}

On the hosted connector at https://agent402.tools/mcp, catalog.call runs solidity-scan free (rate-limited, no wallet). Local install: npx -y agent402-mcp.

Errors and behavior

• source is required. An input the tool rejects returns an HTTP 4xx whose body carries error, tool, expected, required and example, so the caller can correct it.
• A paid call that ends in any status of 400 or above is not charged over x402, MPP or a prepaid credits key: settlement is cancelled when the tool fails. The exception is a Tempo push credential, a transfer the buyer sent before the call: it settles before the tool runs, so if the tool then fails the payment is recorded as a refund owed to the paying wallet.
• Free tier: no outbound network call leaves the server for this tool, so proof-of-work (16 leading zero bits of sha256) pays for it.
• A GET or HEAD to /api/solidity-scan returns the same 402 quote, so the price can be read without a body.
• An Idempotency-Key header makes a retried paid call replay the first 200 instead of charging again (an answer larger than 1 MB is not replayed).

Paid call (JavaScript agent)

import { wrapFetchWithPayment } from "@x402/fetch";
import { x402Client } from "@x402/core/client";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

const client = new x402Client();
client.setSpendControls?.(false); // keep your own spending ceiling in code
registerExactEvmScheme(client, { signer: privateKeyToAccount(KEY) });
const payFetch = wrapFetchWithPayment(fetch, client);

const res = await payFetch("https://agent402.tools/api/solidity-scan", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "source": "pragma solidity ^0.8.0;\ncontract Wallet {\n  function drain(address payable to) external {\n    require(tx.origin == msg.sender);\n    to.call{value: address(this).balance}(\"\");\n  }\n}"
  }),
});

No wallet? Pay with compute

Fetch a challenge, solve the sha256 puzzle (16 leading zero bits, a fraction of a second of CPU), and resend with the X-Pow-Solution header:

import { createHash } from "node:crypto";
const lz = (b) => { let t = 0; for (const x of b) { if (!x) { t += 8; continue; } t += Math.clz32(x) - 24; break; } return t; };
const c = await (await fetch("https://agent402.tools/api/pow/challenge?slug=solidity-scan")).json();
let n = 0;
while (lz(createHash("sha256").update(c.challenge + ":" + n).digest()) < c.difficulty) n++;
await fetch("https://agent402.tools/api/solidity-scan", { method: "POST", headers: { "X-Pow-Solution": c.token + ":" + n, "Content-Type": "application/json" }, body: JSON.stringify({"source":"pragma solidity ^0.8.0;\ncontract Wallet {\n  function drain(address payable to) external {\n    require(tx.origin == msg.sender);\n    to.call{value: address(this).balance}(\"\");\n  }\n}"}) });

Part of these workflows

Solidity heuristic pattern scan is one step in this skill pack, each sold as a single call:

• Contract audit - Triage a smart contract before an agent interacts with it: verified Solidity source, heuristic vulnerability scan, known-address check, function-selector resolution, and a read-only dry-run of the exact call you plan to make.

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