agents.factstamp.dev

Live 402 challenge

Captured by the enrichment pass, not read just now. Prices can change — always read the 402 the endpoint answers with.

{
  "name": "FactStamp",
  "note": "Pay per call in USDC on Base, or redeem a prepaid pack and send it as a bearer token.",
  "tool": "watch_add",
  "about": {
    "why": "A one-off lookup answers what was true when you asked. A watch keeps asking, and tells you when the answer changes: a retraction, a new advisory, a yanked version.",
    "read": "GET /watch/<watch_id> with the token the purchase returned, as `authorization: Bearer <token>`.",
    "stop": "POST /watch/<watch_id>/stop with the same token. Unused days are not refunded.",
    "what": "A standing re-check of one citation or one package version.",
    "events": [
      "citation: retracted, notice_withdrawn, record_changed",
      "package: advisory_added, yanked, deprecated, record_changed"
    ],
    "buy_mcp": "Call the watch_add tool on the paid MCP door, US$0.5 a watch on the per-call rail.",
    "credits": 10,
    "product": "watch",
    "webhook": "Optional: send an https URL at purchase and each change is POSTed to it as JSON. The event is recorded and its receipt issued whether or not the webhook is reachable.",
    "buy_http": "POST /watch {\"kind\":\"citation\",\"query\":\"10.1038/nature12373\"} with a pack code; or {\"kind\":\"package\",\"package\":\"express@4.18.2\",\"ecosystem\":\"npm\"}",
    "receipts": "The purchase answer carries a signed receipt for the first check, and every recorded change carries its own.",
    "price_usd": 0.5,
    "term_days": 30,
    "cadence_hours": 24,
    "price_base_units": "500000"
  },
  "error": "This path answers a GET/HEAD probe with its price rather than a refusal: the terms below are the ones a POST is charged against, at this same resource. Send POST to buy.",
  "packs": "https://agents.factstamp.dev/packs",
  "accepts": [
    {
      "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
      "extra": {
        "name": "USD Coin",
        "version": "2"
      },
      "payTo": "0xc3bcd24a2b350cc73b8516b2a0539a323b42cc32",
      "amount": "500000",
      "scheme": "exact",
      "network": "eip155:8453",
      "mimeType": "application/json",
      "resource": "https://agents.factstamp.dev/watch",
      "description": "A standing re-check of ONE citation or package version, for an answer that must stay true for a month rather than once: daily re-checks for 30 days. US$0.50 the month — 1.7 cents a check, under a 2-cent lookup. The first check is answered and signed on purchase, and each real change (a retraction, a new advisory, a yanked version) gets its own signed receipt. One subject only: for a list use /watch/portfolio. Pay per call here, or redeem a pack code (10 credits).",
      "serviceName": "FactStamp",
      "maxAmountRequired": "500000",
      "maxTimeoutSeconds": 300
    }
  ],
  "resource": "https://agents.factstamp.dev/watch",
  "discovery": "https://agents.factstamp.dev/.well-known/x402",
  "price_usd": 0.5,
  "uncharged": "unknown is a valid answer: a call that returns no answer is not charged on a pack.",
  "extensions": {
    "bazaar": {
      "info": {
        "input": {
          "body": {
            "kind": "citation",
            "subject": "10.1038/nature12373",
            "webhook": "https://example.com/factstamp/hook"
          },
          "type": "http",
          "method": "POST",
          "bodyType": "application/json"
        },
        "output": {
          "type": "json",
          "example": {
            "kind": "citation",
            "token": "fw_9d1c… (shown once)",
            "subject": "10.1038/nature12373",
            "read_url": "https://factstamp.agentrails.workers.dev/watch/9f2c1ab4d0e57718",
            "watch_id": "9f2c1ab4d0e57718",
            "paid_with": {
              "rail": "x402_pay_per_call",
              "settlement": {
                "success": true
              },
              "list_price_usd": 0.5
            },
            "expires_at": "2026-11-05T06:30:00.000Z",
            "receipt_url": "https://factstamp.agentrails.workers.dev/r/8bd1f0a4c9e27715",
            "next_check_at": "2026-10-07T06:30:00.000Z",
            "seeded_verdict": "verified"
          }
        }
      },
      "schema": {
        "type": "object",
        "$schema": "https://json-schema.org/draft/2020-12/schema",
        "required": [
          "input",
          "output"
        ],
        "properties": {
          "input": {
            "type": "object",
            "required": [
              "type",
              "method"
            ],
            "properties": {
              "body": {
                "type": "object"
              },
              "type": {
                "const": "http"
              },
              "method": {
                "const": "POST"
              },
              "bodyType": {
                "const": "application/json"
              }
            },
            "additionalProperties": true
          },
          "output": {
            "type": "object",
            "required": [
              "type",
              "example"
            ],
            "properties": {
              "type": {
                "const": "json"
              },
              "example": {
                "type": "object"
              }
            },
            "additionalProperties": true
          }
        },
        "additionalProperties": false
      }
    }
  },
  "description": "FactStamp — A standing re-check of ONE citation or package version, for an answer that must stay true for a month rather than once: daily re-checks for 30 days. US$0.50 the month — 1.7 cents a check, under a 2-cent lookup. The first check is answered and signed on purchase, and each real change (a retraction, a new advisory, a yanked version) gets its own signed receipt. One subject only: for a list use /watch/portfolio. Pay per call here, or redeem a pack code (10 credits).",
  "x402Version": 2,
  "what_you_get": "Every answer is dated, names the publisher it cites, and carries a receipt that verifies offline without calling us again.",
  "sample_answers": "https://agents.factstamp.dev/samples",
  "zero_knowledge": {
    "buys": "A salted commitment in the receipt, which proves what you bought and opens to nobody else.",
    "page": "https://agents.factstamp.dev/ledger/zero-knowledge",
    "price": {
      "usd": 25,
      "atomic": "25000000",
      "currency": "USDC"
    },
    "option": "zero_knowledge",
    "accepts": [
      {
        "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
        "extra": {
          "name": "USD Coin",
          "version": "2"
        },
        "payTo": "0xc3bcd24a2b350cc73b8516b2a0539a323b42cc32",
        "amount": "25500000",
        "scheme": "exact",
        "network": "eip155:8453",
        "mimeType": "application/json",
        "resource": "https://agents.factstamp.dev/watch",
        "description": "A standing re-check of ONE citation or package version, for an answer that must stay true for a month rather than once: daily re-checks for 30 days. US$0.50 the month — 1.7 cents a check, under a 2-cent lookup. The first check is answered and signed on purchase, and each real change (a retraction, a new advisory, a yanked version) gets its own signed receipt. One subject only: for a list use /watch/portfolio. Pay per call here, or redeem a pack code (10 credits). Zero knowledge: the ledger entry is blind.",
        "maxAmountRequired": "25500000",
        "maxTimeoutSeconds": 300
      }
    ],
    "available": true,
    "publishes": [
      "entry_id",
      "day",
      "price",
      "scheme",
      "network"
    ],
    "withholds": [
      "the door this call was sold at",
      "the request and any fingerprint of it",
      "the answer and any fingerprint of it",
      "the receipt signature",
      "the payer's wallet address"
    ],
    "not_hidden": "The USDC transfer itself is public chain data: the payment rail is not ours, so when and how much you paid stays visible. What the option hides is what you asked.",
    "select_with": {
      "header": "x-factstamp-privacy: zero_knowledge",
      "body_field": "privacy: \"zero_knowledge\""
    },
    "included_state": {
      "option": "public_ledger",
      "sold_as": "Included in the door price. The call is appended to the public FactStamp Ledger with a fingerprint of the request, a fingerprint of the answer and the door name.",
      "price_added_usd": 0,
      "price_added_atomic": "0"
    },
    "total_per_call": {
      "usd": 25.5,
      "atomic": "25500000",
      "currency": "USDC",
      "door_price_usd": 0.5,
      "door_price_atomic": "500000"
    },
    "added_to_door_price_atomic": "25000000"
  },
  "amount_base_units": "500000"
}

Accepts

The payment requirements as published to the catalog. Read the live 402 before paying — a price here is a claim, not a quote.

[
  {
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "extra": {
      "name": "USD Coin",
      "version": "2"
    },
    "payTo": "0xc3bcd24a2b350cc73b8516b2a0539a323b42cc32",
    "scheme": "exact",
    "network": "eip155:8453",
    "mimeType": "application/json",
    "resource": "https://agents.factstamp.dev/watch",
    "description": "A standing re-check of ONE citation or package version, for an answer that must stay true for a month rather than once: daily re-checks for 30 days. US$0.50 the month — 1.7 cents a check, under a 2-c…",
    "maxAmountRequired": "500000",
    "maxTimeoutSeconds": 300
  }
]

Provenance

Seen in the source catalog

2026-10-20 03:36Z

Last indexed by Roundhouse

2026-10-24 02:46Z

Last enriched (probe, favicon, geo)

2026-10-24 08:16Z

x402 version

1

Max timeout

300s

Liveness probe

HTTP 402