The full upstream README, mirrored here for reference. Install config, tool schemas, adoption signals, and an original overview live on the Crosscheck listing page.
Independent checks for AI agents, paid per call over x402:
Agents write emails, reports, client messages, and PR descriptions. The agent that wrote a draft is the worst one to check it. crosscheck is a separate reviewer: your agent sends the text and gets back a verdict, either pass or a list of specific issues with fixes, plus an Ed25519-signed receipt.
Each check costs $0.02 in USDC on Base, paid per request over x402. There is no account, no API key, and no subscription. You can try it for free with test USDC on Base Sepolia, up to 10 checks per wallet per day.
[NAME] placeholders, TODOs, and content the draft promises but does not contain ("the three options below", followed by one).Agents increasingly buy work from other agents: research, data, code, drafts. The buyer needs to know the work meets the task before it pays. Send the task you gave and the deliverable you got back:
You get accept or reject, with every requirement judged:
(The two requirements that passed are left out here.) Counts, required JSON fields, and figures are checked in code, not by the model. A deliverable that claims its own completeness, or tries to talk the checker into accepting, never passes. The signed receipt holds hashes of the task and the deliverable and your optional reference (an order id or transaction hash), so both agents can see exactly what was checked.
Skills and MCP servers run with your agent's access to files, keys, and money, and malicious ones are common on public registries. skillcheck reads a skill's files (never runs them) and reports what they could do: downloads piped into a shell, reads of SSH keys, cloud credentials, and wallets, environment variables sent over the network, persistence, lookalike (typosquatted) package names, invisible characters, and instructions aimed at your agent or at the scanner. Code rules catch the known patterns; the review model judges intent against what the skill says it does.
Results are keyed to the SHA-256 of the files, so a skill someone already scanned is looked up free. The verdict never says "safe": no_findings means nothing was found in the files sent.
Skill authors: scan your own skill and add the badge_markdown from the result to your README. The badge links to a signed proof page for that exact version of your files, so agents deciding whether to install it can see it was checked.
Claude Code:
Or install the Claude Code plugin, which adds the MCP server and the skill together. Set CROSSCHECK_WALLET_KEY in your environment before starting Claude Code; the plugin reads it from there and never stores it:
Any client that takes an mcpServers block (Claude Desktop, Cursor, Windsurf, and others):
VS Code, Codex CLI, and other setups are in examples/mcp. The server has five tools: quote (free), order (checks a draft), accept (checks work another agent handed back), skillcheck (scans a skill or server before install), and result (free).
Use a dedicated wallet that holds a few dollars of USDC on Base, never your main wallet. The client refuses any price above CROSSCHECK_MAX_USD (default 0.10). To try it without real money, get test USDC from https://faucet.circle.com and add "CROSSCHECK_NETWORKS": "eip155:84532" to env.
crosscheck also runs as a remote MCP server at https://crosscheckapi.com/mcp (Streamable HTTP). Its tools are check, accept, skillcheck, skillcheck_lookup (free), verify_receipt (free: confirms a crosscheck receipt is genuine and covers exactly the text you were handed), and result (free). Paid tools follow the x402 MCP transport: the first call returns the price as an x402 PaymentRequired error result, and an x402-aware client (for example one built with @x402/mcp) pays and retries with the payment in _meta["x402/payment"]. The settlement comes back in _meta["x402/payment-response"]. Clients that cannot pay can still use the free tools, or run the npm server above, which pays from your wallet.
A tool only helps if the agent calls it. Put these in your agent's system prompt:
Before you give your human any draft that contains numbers, dates, money, or commitments, or that will be sent to someone else, call crosscheck's
ordertool with the full draft exactly as your human will see it. Fix every blocker and major issue it reports. Say the draft was checked only if the verdict passed.
Before you pay for work another agent or service delivered, or pass it on, call crosscheck's
accepttool with the task you gave and the deliverable exactly as received. Pay or use it only if accept is true; otherwise send the blocking requirements back.
Any x402 v2 client works. POST {"draft": "..."} to https://crosscheckapi.com/v1/check, pay the 402 (scheme exact, network eip155:8453), and send the same request again with the payment header. Payment settles before the review runs.
npx -p crosscheckapi crosscheck order draft.txtThe full API is in skill/crosscheck/references/API.md, and the always-current summary is at https://crosscheckapi.com/llms.txt.
pass is true when there are no blocker or major issues. Minor issues may still be listed.
| Draft size | Price |
|---|---|
| Up to 12,000 units (about 12,000 English characters) | $0.02 |
| Each further 12,000 units | +$0.01 |
| Maximum | 48,000 units, $0.05 |
A unit is one character, or half the UTF-8 byte length when that is larger, so most non-Latin text and emoji count 1.5 to 2 units per character. A quote is free. A pass costs the same as a fail.
Every paid check returns a receipt covering the SHA-256 of your draft (never the text), the payment, and the SHA-256 of the verdict. It is signed with Ed25519 and chained into an append-only ledger. Each result also comes with a share_url, a public page showing the outcome, time, payment, and hashes (never your text), so an agent can link proof that its work was checked. The client verifies it automatically against https://crosscheckapi.com/.well-known/crosscheck-keys.json and reports receipt_check.valid, so you can show your human proof of what was checked and when.
The draft is sent to crosscheck and to its review model (Claude, through Anthropic's API), then deleted when the check finishes. Only its hash is kept. Verdicts are kept for 30 days so you can fetch them again, then deleted. Do not send text your human has marked confidential.
crosscheckapi, the MCP server and CLI. npm ci && npm run build rebuilds bin/ byte for byte, matching the checksums in skill/crosscheck/SHA256SUMS.SKILL.md, the API reference, and the bundled client. Install it with one command:
com.crosscheckapi/crosscheck.The review service itself is not in this repository.
x402 Bazaar · MCP Registry · npm · ClawHub · llms.txt · OpenAPI
MIT