{"name":"crosscheck","description":"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.","supportedInterfaces":[{"url":"https://crosscheckapi.com/a2a","protocolBinding":"JSONRPC","protocolVersion":"1.0"},{"url":"https://crosscheckapi.com/a2a","protocolBinding":"JSONRPC","protocolVersion":"0.3"}],"protocolVersion":"0.3.0","url":"https://crosscheckapi.com/a2a","preferredTransport":"JSONRPC","provider":{"organization":"crosscheck","url":"https://crosscheckapi.com"},"version":"1.0.0","documentationUrl":"https://crosscheckapi.com/llms.txt","iconUrl":"https://crosscheckapi.com/icon.png","capabilities":{"streaming":false,"pushNotifications":false,"extensions":[{"uri":"https://github.com/google-agentic-commerce/a2a-x402/blob/main/spec/v0.2","description":"Paid skills use x402 payments (USDC on Base; free test USDC on Base Sepolia), standalone flow.","required":false}]},"defaultInputModes":["application/json","text/plain"],"defaultOutputModes":["application/json"],"skills":[{"id":"check","name":"Review a draft","description":"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.","tags":["review","fact-check","hallucination","grounding","proofread"],"examples":["{\"skill\": \"check\", \"draft\": \"Q3 revenue rose 12% to $4.2M...\"}","Or send the draft as plain text."],"inputModes":["application/json","text/plain"],"outputModes":["application/json"]},{"id":"accept","name":"Check a deliverable against its task","description":"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.","tags":["acceptance-test","verify-deliverable","escrow","agent-commerce"],"examples":["{\"skill\": \"accept\", \"task\": \"List 5 Base RPC endpoints as JSON\", \"deliverable\": \"[...]\"}"],"inputModes":["application/json"],"outputModes":["application/json"]},{"id":"skillcheck","name":"Security review of a skill or MCP server","description":"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.","tags":["security","mcp","skill-security","prompt-injection","malware-scan"],"examples":["{\"skill\": \"skillcheck\", \"files\": [{\"path\": \"SKILL.md\", \"content\": \"...\"}]}"],"inputModes":["application/json"],"outputModes":["application/json"]},{"id":"skillcheck_lookup","name":"Look up a past skillcheck","description":"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}).","tags":["security","lookup","free"],"examples":["{\"skill\": \"skillcheck_lookup\", \"bundle_sha256\": \"<64 hex>\"}"],"inputModes":["application/json"],"outputModes":["application/json"]},{"id":"verify_receipt","name":"Verify a crosscheck receipt","description":"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.","tags":["verify","receipt","trust","free"],"examples":["{\"skill\": \"verify_receipt\", \"receipt_hash\": \"<64 hex>\", \"task\": \"...\", \"deliverable\": \"...\"}"],"inputModes":["application/json"],"outputModes":["application/json"]}]}