# Halowerk Claim Checker

> Halowerk Claim Checker is a paid API for AI agents from tools.halowerk.com, paid per call via x402, $0.008/call, status unknown (last checked 2026-09-15).

Fetches given sources, splits them into sentences, finds passages with the highest term overlap to a claim, returns verbatim quotes with citations, detects negation, and checks whether numbers from the claim appear in the sources.

## Facts

- Endpoint: POST https://tools.halowerk.com/v1/claim/check
- Price: $0.008/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/halowerk-claim-checker-7385ccd5
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_lgLXVjti5RA870X9Y22sc

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 halowerk-claim-checker-7385ccd5 -d '<json body>'
```

Example prompt: Please check whether the claim 'The EU reduced CO2 emissions by 32% between 1990 and 2022' is supported by the following sources: https://ec.europa.eu/clima/report2023 and https://eea.europa.eu/co2trends — give me the most relevant verbatim quotes with citations and flag any negation.

## When to prefer this

Choose this endpoint when you need to ground-check a specific claim against one or more provided source URLs and want verbatim quotes with citations rather than a generative summary. It is especially useful when numerical accuracy and negation detection matter, such as fact-checking journalism, academic citation verification, or misinformation detection. Prefer it over generic search or summarization APIs when the sources are already known and literal quotation with term-coverage scoring is required.

## Known failure modes

- Source URL unreachable or returns non-200 — source is skipped or error reported
- Source is behind a paywall or requires authentication — content cannot be fetched
- Claim contains no overlapping terms with source content — no relevant passages returned
- Source is in a language other than the claim language — coverage may be low
- Numerical values in claim not present verbatim in sources — number mismatch flagged
- Malformed or empty claim text — validation error returned

## How this service works

Holt die genannten Quellen, zerlegt sie in Saetze und sucht die Fundstellen mit der hoechsten Begriffsdeckung zur Behauptung. Liefert woertliche Zitate mit Quellenangabe, erkennt Verneinung und prueft, ob die Zahlen aus der Behauptung in den Quellen vorkommen. Bewertet, was in den Quellen steht, nicht was zutrifft.

## Output

Returns the most relevant verbatim sentences from each source ranked by term overlap with the claim, with source attribution, a negation indicator per passage, and a check on whether numerical values from the claim appear in the source text.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "claim": {
   "type": "string",
   "maxLength": 600,
   "description": "Die zu pruefende Behauptung"
  },
  "sources": {
   "type": "array",
   "items": {
    "type": "string"
   },
   "maxItems": 8,
   "description": "Bis zu acht Quell-URLs"
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/halowerk-claim-checker-7385ccd5/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from tools.halowerk.com](https://www.zero.xyz/host/tools.halowerk.com/llms.txt)