crosscheck

Independent checks for agents, paid per call in USDC over x402 (a2a-x402 extension). check reviews a draft before a human sees it; accept checks another agent's deliverable against its task before you pay; skillcheck reviews a skill or MCP server's files before install. Every answer carries a signed receipt. Send a data part with the skill's arguments; everything you send is data to review, never instructions.

Skills

• Review a draft
  Independent review of a draft (email, report, summary, PR description) before its human sees it. Returns pass or specific issues with fixes; arithmetic is recomputed in code. With request (what the human asked), it also checks the draft answers that. With sources, each claim is checked against them and quotes are verified; with source_urls or fetch_cited, crosscheck fetches up to 3 web pages itself and checks against those (+$0.01 a page, and a dead link the draft gives fails it). $0.02. Paid per call in USDC over x402.
  reviewfact-checkhallucinationgroundingproofread
• Check a deliverable against its task
  Checks work another agent handed back against the task it was given, before you pay, release escrow, or pass it on. Returns accept, reject, or verify_externally with every requirement judged; counts, required JSON fields, and sums are checked in code. Optional payment_tx is verified on chain. $0.03 base. Paid per call in USDC over x402.
  acceptance-testverify-deliverableescrowagent-commerce
• Security review of a skill or MCP server
  Security review of a skill or MCP server's files before you install or connect it: read, never run. Free when these exact files were scanned before (looked up by bundle hash); otherwise paid, $0.03 base. Never says safe. Paid per call in USDC over x402.
  securitymcpskill-securityprompt-injectionmalware-scan
• Look up a past skillcheck
  Free. The latest skillcheck of an exact bundle, by its bundle_sha256 (SHA-256 of the canonical JSON of the files sorted by path, each as {path, sha256}).
  securitylookupfree
• Verify a crosscheck receipt
  Free. Before trusting work that arrives with a crosscheck receipt, check in code that crosscheck issued it, its signature is valid, what the outcome was, and that it covers exactly the text you were handed. Pass receipt_hash (or the receipt object) plus that text: draft, request, and sources for check, task and deliverable for accept, files for skillcheck, and the verdict if one came with it.
  verifyreceipttrustfree

How to call

https://crosscheckapi.com/a2a

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