---
title: "Anti-hallucination checker for legal references - verify..."
method: POST
path: "/api/law/citation-check"
tags: ["law"]
---

# Anti-hallucination checker for legal references - verify...

`POST /api/law/citation-check`

## Request

- Base URL: `https://2s.io`
- URL: `https://2s.io/api/law/citation-check`
- Auth: API key in header `PAYMENT-SIGNATURE`

Anti-hallucination checker for legal references — verify that cited cases, US Code sections, and CFR regulations in a passage actually EXIST, and (deterministically) that an attributed QUOTE actually appears in the cited opinion. POST { text } to scan a brief/passage: every case citation (via CourtListener), 'N U.S.C. § X', and 'N C.F.R. § X' is checked for existence with canonical metadata + a source URL, or flagged unverified. POST { quotes: [{ citation, quote }] } to verify specific quotations: each citation is resolved and its opinion full text is checked for the quote (ellipsis-aware), returning quote.present true/false. Pass both. Returns per-reference results + a summary (verified/unverified, quotesPresent/quotesMissing). Catches fabricated cases AND fabricated quotations — the LLM legal-output failure mode that gets attorneys sanctioned. Note: this checks existence + quote presence (facts), NOT whether a case legally supports a proposition. Sources: CourtListener (Free Law Project), US OLRC, eCFR (public domain).

## Query parameters

- `trial` 1

## Request body

- object
  - `text` string: Text.
  - `quotes` object[]: Quotes.
    - `citation` string, required: Citation.
    - `quote` string, required: Quote.

## Other responses

- `200` (unresolved $ref)
- `400`: Invalid request — not charged. error.code: BAD_REQUEST or INVALID_PARAM (parameter validation; error.details.issues lists each problem), MALFORMED_JSON, or a request-specific code. Other client errors: 405 METHOD_NOT_ALLOWED (wrong verb; see the Allow header), 413 PAYLOAD_TOO_LARGE.
- `402`: Payment required. Body is the x402 PaymentRequirements envelope with a multi-network accepts array; the per-call price is in accepts[].amount (and on the operation as x-2s-price). Sign for whichever rail you hold USDC on (EIP-3009 for Base, partial SPL transfer for Solana) and retry with the PAYMENT-SIGNATURE header (X-PAYMENT also accepted for v1 clients). Also PAYMENT_SETTLE_FAILED (error envelope) when a verified payment failed to settle: error.details.chargeStatus is "not_charged" (retry with a fresh payment) or "unknown" (the authorization may still settle before its deadline — check it before retrying).
- `404`: Not found — NOT_FOUND (or NO_SOURCES / NO_OPINIONS): the requested entity does not exist. Not charged.
- `429`: Too many requests — RATE_LIMITED: our per-IP / per-payer limiter. Not charged; retry after Retry-After.
- `5XX`: Server-side failure. 500 INTERNAL: unexpected error; quote error.errorId (also the X-2s-Error-Id header). 502 UPSTREAM_UNAVAILABLE (or another UPSTREAM_* code): the data provider failed — composite endpoints refuse unbilled when every source fails. 503 SERVICE_PAUSED: endpoint paused by the operator kill switch, retry after Retry-After; 503 SPEND_CAP: daily upstream budget exhausted. 504 UPSTREAM_TIMEOUT. Not charged.

---

[API](https://skmtc.dev/2s-io/apis/2s-the-most-everything-api.md) · [All operations](https://skmtc.dev/2s-io/apis/2s-the-most-everything-api/llms.txt) · [OpenAPI document](https://skmtc.dev/2s-io/apis/2s-the-most-everything-api/revisions/da4c5caf686e?raw)