# Concordance Corroboration Checker

> Concordance Corroboration Checker is a paid API for AI agents from concordancehq.duckdns.org, paid per call via x402, $0.04/call, status unknown (last checked 2026-10-29).

Checks whether a claim is independently corroborated across multiple unrelated sources, returning a breakdown by source outlet so callers can assess how many independent agencies back the claim.

## Facts

- Endpoint: POST https://concordancehq.duckdns.org/tools/corroboration?utm_source=zero.xyz
- Price: $0.04/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-29
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/concordance-corroboration-checker-1ed932af
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_8hHLu-CkHglgBoUT2Qzj-

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 concordance-corroboration-checker-1ed932af -d '<json body>'
```

Example prompt: Check how many independent sources corroborate the claim 'The Federal Reserve raised interest rates by 0.5% in March 2024' — pull up to 50 results and only look at articles since January 2024, then tell me how many distinct outlets confirm it.

## When to prefer this

Choose this endpoint when you need to distinguish true multi-source corroboration from echo-chamber repetition — i.e., when you want to know how many genuinely independent outlets confirm a claim, not just how many articles mention it. Prefer this over a plain search endpoint when the trust signal matters: verifying news credibility, conducting due diligence, or detecting single-origin misinformation. Use it when source independence (not just volume) is the key metric.

## Known failure modes

- Claim too vague or ambiguous to match any sources — returns zero corroboration results
- Date filter (since) excludes all relevant coverage — empty result set
- Raw pull limit set too low — may miss corroborating sources and undercount independent backing
- Claim is very recent and no sources have indexed it yet — low or zero results
- Claim contains highly domain-specific jargon not indexed in aggregated sources

## How this service works

Is a claim independently corroborated across multiple unrelated sources, or does it trace back to a single origin? Groups matches by SOURCE (not category) so a caller sees exactly how many independent outlets/agencies back a claim -- a trust signal no single-source competitor can offer, since it requires already owning many independent sources.

## Output

A breakdown of how many and which independent source outlets corroborate the submitted claim, grouped by source (not category), enabling the caller to see exactly how many distinct, unrelated agencies back the claim versus how many trace back to a single origin.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "claim": {
   "type": "string"
  },
  "since": {
   "type": "string"
  },
  "raw_pull_limit": {
   "type": "integer"
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/concordance-corroboration-checker-1ed932af/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from concordancehq.duckdns.org](https://www.zero.xyz/host/concordancehq.duckdns.org/llms.txt)