# shelf.thirdmade.net Hallucination Check

> shelf.thirdmade.net Hallucination Check is a paid API for AI agents from shelf.thirdmade.net, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-14).

Scores whether a provided context passage entails or supports a given claim, helping research agents self-verify their outputs.

## Facts

- Endpoint: GET https://shelf.thirdmade.net/probe/hallucination-check
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/shelf-thirdmade-net-hallucination-check-09f2fb06
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_ylTlonLFuaglz4KrZsFhy

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 shelf-thirdmade-net-hallucination-check-09f2fb06
```

Example prompt: Check whether this passage — 'Aspirin was first synthesized in 1897 by Felix Hoffmann at Bayer' — actually supports the claim 'Aspirin was invented in the 19th century by a German chemist.'

## When to prefer this

Choose this endpoint when you need a lightweight, per-claim entailment check to verify that agent-generated text is grounded in retrieved context — especially in RAG pipelines, research automation, or any workflow where hallucination risk must be bounded before output is surfaced to users. Prefer this over general-purpose LLM self-critique when you need a deterministic, scoreable signal rather than a free-text explanation.

## Known failure modes

- Missing 'context' or 'claim' query parameter returns a 400 error
- Very long context or claim strings may be truncated or rejected
- Ambiguous or semantically empty claims may produce low-confidence mid-range scores
- Payment failure (x402) if USDC balance is insufficient
- Service unavailability returns 5xx if GPU/model backend is down

## How this service works

Entailment scoring: does the provided context support this claim? Research agents use this to self-check outputs.

## Output

Returns an entailment score indicating how strongly the provided context passage supports the given claim, allowing agents to quantify whether their outputs are grounded in evidence or potentially hallucinated.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "context",
      "claim"
     ],
     "properties": {
      "claim": {
       "type": "string",
       "description": "Claim to check"
      },
      "context": {
       "type": "string",
       "description": "Evidence/context text"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/shelf-thirdmade-net-hallucination-check-09f2fb06/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from shelf.thirdmade.net](https://www.zero.xyz/host/shelf.thirdmade.net/llms.txt)