API documentation

One question per call: does this specific source support this specific claim?

What it verifies — and what it does not

• It checks the relationship between one claim and one source you name. It does not search the web for other sources.
• It does not decide whether a claim is true in the world. NOT_FOUND_IN_SOURCE is not evidence that a claim is false.
• It does not provide legal, medical or financial advice.
• Compound claims are split into components; support for only some of them yields PARTIALLY_SUPPORTED.

Request

POST https://sourceclaimverification.online/api/v1/verify
Content-Type: application/json
Idempotency-Key: <random, 16-128 chars of A-Z a-z 0-9 _ ->   (required; also your result access token)
PAYMENT-SIGNATURE: <x402 payload>                              (second call, after the 402)

{
  "claim": "The company reported revenue of $3.2 billion in 2025.",   // required, ≤ 1000 chars
  "source_url": "https://example.com/report",                          // or source_text (exactly one)
  "source_text": "…",                // ≤ 100000 chars; reported as provided_by_requester
  "source_label": "Annual report PDF, p. 12",   // optional, with source_text
  "output_language": "ja",           // optional BCP-47; default: the claim's language, else en
  "source_language": "de",           // optional hint when the page does not declare it
  "strictness": "standard",          // or "strict": SUPPORTED only on direct/secondary statements
  "max_source_age_seconds": 600      // cached copy allowed up to this age; 0 forces a fresh fetch
}

Payment (x402)

1. Send the request without payment. You receive HTTP 402 with the requirement in the JSON body and the PAYMENT-REQUIRED header (x402 v2, scheme exact, USDC on Base mainnet (eip155:8453)).
2. Sign an EIP-3009 authorization for exactly 0.048 USDC to the listed payTo, valid for at least 90 seconds.
3. Repeat the identical request with the same Idempotency-Key and a PAYMENT-SIGNATURE header. The PAYMENT-RESPONSE header returns the settlement.

One price per verification, quoted before any work and bound into the x402 payment requirement. You are charged only when the source was retrieved and a verdict was produced: SOURCE_UNAVAILABLE and model/provider failures are not charged (the payment authorization is not settled). Requests rejected by validation are never charged. Retrying with the same Idempotency-Key never charges twice.

The verdict is released only after the payment settles. If retrieval fails, the result is SOURCE_UNAVAILABLE and the authorization is not settled. If the model provider fails, you get HTTP 503 with retryable: true: resend the same request with the same key and payment while the authorization is valid. One payment authorization can buy only one request; reusing it for a different request returns HTTP 409.

Free validation: POST /api/v1/quote with the same body checks the schema, URL safety and DNS, and returns the price — without payment, retrieval or model use.

Verdicts

Confidence (HIGH / MEDIUM / LOW) describes how clearly the source settles the relationship — evidence quality, how much of the source was examined, and whether deterministic checks intervened. It is not a probability that the claim is true.

Response

{
  "object": "claim_verification",
  "verification_id": "5d0c…",
  "verdict": "PARTIALLY_SUPPORTED",
  "verdict_label": "Partially supported",
  "confidence": "MEDIUM",
  "scope": "claim_to_source_relationship",
  "claim": {
    "text": "Company X cut prices by 20% in January 2026.",
    "language": "en"
  },
  "source": {
    "url": "https://example.com/news",
    "final_url": "https://example.com/news",
    "title": "Company X trims prices",
    "published_at": "2026-03-04T08:00:00.000Z",
    "retrieved_at": "2026-09-30T12:00:00.000Z",
    "language": "en",
    "content_sha256": "9f2c…",
    "cache": {
      "used": false,
      "original_retrieved_at": null
    },
    "examination": {
      "passages_total": 42,
      "passages_examined": 42,
      "complete": true,
      "method": "full_text"
    },
    "provided_by_requester": false
  },
  "evidence": [
    {
      "passage": "Company X cut selected product prices by up to 20% in March 2026.",
      "language": "en",
      "location": {
        "passage_id": "p3",
        "block_index": 2,
        "heading": "Pricing",
        "char_start": 311
      },
      "relation": "PARTIALLY_SUPPORTS",
      "assertion_type": "DIRECT_SOURCE_STATEMENT",
      "attributed_to": null,
      "translation": null
    }
  ],
  "analysis": {
    "subject_match": true,
    "action_or_fact_match": true,
    "quantity_match": false,
    "time_match": false,
    "qualifiers_preserved": false,
    "missing_qualifiers": [
      "selected products only",
      "up to 20%"
    ],
    "mismatches": [
      {
        "component": "time",
        "claim": "January 2026",
        "source": "March 2026"
      }
    ]
  },
  "explanation": "The source reports cuts of up to 20% on selected products in March, not January.",
  "guards": [],
  "limitations": [],
  "payment": {
    "amount": "0.048",
    "currency": "USDC",
    "charged": true,
    "transaction": "0x…"
  }
}

• evidence[].passage is a short verbatim excerpt in the source's original language (verified character-for-character against the retrieved text). translation, when present, is derived and never replaces the original.
• assertion_type: DIRECT_SOURCE_STATEMENT, ATTRIBUTED_STATEMENT (someone is reported as saying it), SECONDARY_REPORTING (reported as fact based on another source), INFERENCE. A claim supported only by an attributed statement is PARTIALLY_SUPPORTED unless the claim itself is attributed.
• guards lists deterministic checks that changed or qualified the model's answer, e.g. claim_quantity_conflicts_with_evidence, polarity_conflict, attributed_evidence_only, evidence_quantity_is_qualified.
• source.content_sha256 fingerprints the normalized text that was examined; source.cache discloses when a cached copy was used and when it was originally retrieved.
• Language fields hold ISO codes, UNKNOWN (not reliably identifiable) or MULTILINGUAL.

Retrieve a stored result: GET /api/v1/verifications/{request_id} with Authorization: Bearer <Idempotency-Key>.

Source retrieval

• Public HTML, plain text and JSON over http/https (ports 80/443). Up to 5 redirects, 3 MB, 12 s.
• Static retrieval only in this version: pages that render their content with JavaScript, PDFs and office documents return SOURCE_UNAVAILABLE — send their text as source_text.
• No bypass of logins, paywalls, CAPTCHAs, bot challenges or rate limits (HTTP 401/402/403/429 → SOURCE_UNAVAILABLE, not charged).
• Loopback, private, link-local, carrier-grade NAT and cloud metadata addresses are refused, for the first request, every redirect, and every DNS answer.
• Page content is untrusted data: instructions written inside a page are ignored.
• Large pages are reduced to the passages most relevant to the claim (≈3500 tokens; ≈6000 when claim and source languages differ). source.examination reports how much was examined.

Errors

Errors are JSON: { error: { code, message } }. 400 validation / unsafe URL, 402 payment required or rejected, 409 key or payment reuse, 413 too large, 415 wrong content type, 429 rate limited (per client, per minute), 503 not configured / provider failure / settlement reconciliation. None of the 4xx responses are charged.

Languages

Claims and sources may be in any language and need not match (for example an English claim against a Japanese source). Explanations follow output_language; quoted evidence stays in the original. The website is in English; the service is not English-only.