# AIAlign Hallucination Rate - Lexical Coverage Screener

> AIAlign Hallucination Rate - Lexical Coverage Screener is a paid API for AI agents from aialign.halowerk.com, paid per call via x402, $0.004/call, status unknown (last checked 2026-09-16).

Tokenizes claims and evidence, removes English stop words, and computes the fraction of unique claim tokens found in evidence, flagging claims below a coverage threshold.

## Facts

- Endpoint: POST https://aialign.halowerk.com/v1/hallucination-rate
- Price: $0.004/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-16
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/aialign-hallucination-rate-lexical-coverage-screener-35aa057f
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_7YOOT2t9m0EfRETRFZ-nw

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability aialign-hallucination-rate-lexical-coverage-screener-35aa057f -d '<json body>'
```

Example prompt: Screen these 3 AI-generated claims against their supporting evidence passages for lexical grounding — flag any claim where fewer than 60% of its unique tokens appear in the evidence: claim 1 says 'The Eiffel Tower is 330 meters tall', claim 2 says 'Paris has a population of 2 million', claim 3 says 'The tower was built in 1889'.

## When to prefer this

Choose this endpoint when you need a fast, cheap, deterministic lexical screening of LLM output grounding — especially in batch eval pipelines, CI/CD model testing, or RAG output auditing where you want a first-pass signal on which claims lack evidence token overlap. It is not a semantic entailment checker or a truth verifier; prefer it over heavier NLI/embedding-based approaches when speed and cost matter and you understand its lexical-only limitations.

## Known failure modes

- Empty claims array returns validation error
- claim_text or evidence_texts exceeding character limits rejected
- minimum_coverage_fraction outside [0,1] range causes validation error
- Very short claims may produce unreliable coverage fractions due to small token counts
- Non-English text may behave unpredictably since stop-word list is English-only
- Payment failure via x402 protocol returns 402 before processing

## How this service works

Tokenizes each claim and its supplied evidence, removes a small declared English stop-word list, and reports the fraction of unique claim tokens present in evidence. Coverage below a supplied threshold is flagged. This is lexical grounding screening only: overlap does not prove truth, low overlap does not prove hallucination, and the service does not retrieve or validate evidence.

## Output

Returns per-claim results including the computed coverage fraction (ratio of unique claim tokens found in evidence), a flag indicating whether coverage fell below the supplied minimum_coverage_fraction threshold, and the original claim_id for cross-referencing.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "claims": {
   "type": "array",
   "items": {
    "type": "object",
    "required": [
     "claim_id",
     "claim_text",
     "evidence_texts"
    ],
    "properties": {
     "claim_id": {
      "type": "string",
      "maxLength": 128,
      "minLength": 1
     },
     "claim_text": {
      "type": "string",
      "maxLength": 20000,
      "minLength": 1
     },
     "evidence_texts": {
      "type": "array",
      "items": {
       "type": "string",
       "maxLength": 50000,
       "minLength": 1
      },
      "maxItems": 100,
      "minItems": 1
     }
    },
    "additionalProperties": false
   },
   "maxItems": 5000,
   "minItems": 1
  },
  "minimum_coverage_fraction": {
   "type": "number",
   "maximum": 1,
   "minimum": 0
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/aialign-hallucination-rate-lexical-coverage-screener-35aa057f/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from aialign.halowerk.com](https://www.zero.xyz/host/aialign.halowerk.com/llms.txt)