crosscheck

{
  "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.",
  "url": "https://crosscheckapi.com/a2a",
  "version": "1.0.0",
  "documentationUrl": "https://crosscheckapi.com/llms.txt",
  "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
      }
    ]
  },
  "authentication": {
    "schemes": [
      "none"
    ]
  },
  "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.",
      "inputModes": [
        "application/json",
        "text/plain"
      ],
      "outputModes": [
        "application/json"
      ],
      "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."
      ]
    },
    {
      "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.",
      "inputModes": [
        "application/json"
      ],
      "outputModes": [
        "application/json"
      ],
      "tags": [
        "acceptance-test",
        "verify-deliverable",
        "escrow",
        "agent-commerce"
      ],
      "examples": [
        "{\"skill\": \"accept\", \"task\": \"List 5 Base RPC endpoints as JSON\", \"deliverable\": \"[...]\"}"
      ]
    },
    {
      "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.",
      "inputModes": [
        "application/json"
      ],
      "outputModes": [
        "application/json"
      ],
      "tags": [
        "security",
        "mcp",
        "skill-security",
        "prompt-injection",
        "malware-scan"
      ],
      "examples": [
        "{\"skill\": \"skillcheck\", \"files\": [{\"path\": \"SKILL.md\", \"content\": \"...\"}]}"
      ]
    },
    {
      "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}).",
      "inputModes": [
        "application/json"
      ],
      "outputModes": [
        "application/json"
      ],
      "tags": [
        "security",
        "lookup",
        "free"
      ],
      "examples": [
        "{\"skill\": \"skillcheck_lookup\", \"bundle_sha256\": \"<64 hex>\"}"
      ]
    },
    {
      "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.",
      "inputModes": [
        "application/json"
      ],
      "outputModes": [
        "application/json"
      ],
      "tags": [
        "verify",
        "receipt",
        "trust",
        "free"
      ],
      "examples": [
        "{\"skill\": \"verify_receipt\", \"receipt_hash\": \"<64 hex>\", \"task\": \"...\", \"deliverable\": \"...\"}"
      ]
    }
  ],
  "protocolVersion": "0.3.0",
  "preferredTransport": "JSONRPC"
}