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Check a claim

Canonical tool: occam_claim_check

Evidence / support lookup over extracted page content: retrieve blocks that clear a lexical BM25 floor for a claim string, attach Merkle membership proofs, and return a signed Receipt v1 for the extract — or an honest found:false.

Not a fact check. verdict is always not_evaluated. The tool does not classify support vs refute. Merkle proofs prove block membership in the signed extract, not that the claim is true.

When to use

  • Grounding a single assertion against one source URL before citing it.
  • Auditing many claims with stance heuristics → occam_attest (unsigned aggregate).
  • Third-party re-check of each returned proof → occam_verify mode=citation.

Parameters

Parameter Type Default Required Description
claim string — yes The assertion to ground (a sentence)
url string — yes HTTP or HTTPS URL to check against
backend_policy string http_then_browser no http, browser, or http_then_browser
session_profile string? null no For gated pages
max_matches int 3 no Max relevant blocks to return (1–10)

Returns

Success envelope:

  • ok: true, url, claim, found — retrieval result, not stance
  • verdict — always not_evaluated (use occam_attest for status)
  • proven — legacy field: when found:false, true means retrieval-complete negative (untruncated leaf set, no BM25 hit). Not semantic proof the page omits the claim. null when found:true.
  • blockMerkleRoot?, keyId? — the signed root proofs anchor to
  • matches[] — retrieved blocks with text, score, leaf, Merkle proof
  • receipt? — signed Receipt v1 for the page extract (verifiable)
  • timestamp

Failure envelope: ok: false — page could not be read (content unknown). Distinct from found:false.

Failure codes

invalid_arguments, plus the transcode fetch taxonomy. See failure codes.

Example

Call:

{
  "claim": "nginx supports weighted round-robin load balancing",
  "url": "https://nginx.org/en/docs/http/load_balancing.html"
}

Trimmed response:

{
  "ok": true,
  "found": true,
  "verdict": "not_evaluated",
  "blockMerkleRoot": "…",
  "keyId": "k1:…",
  "matches": [ { "text": "…weight parameter…round-robin…", "score": 0.71, "leaf": "…", "proof": [ … ] } ],
  "receipt": { "signed": { "contentHash": "sha256:…", "sig": "…" } }
}