# FreshProof Compare

> FreshProof Compare is a paid API for AI agents from freshproof-api-mainnet.up.railway.app, paid per call via x402, $0.02/call, status unknown (last checked 2026-09-14).

Fetches a live copy of a public URL and compares it against a previously stored FreshProof snapshot, returning deterministic fact differences, content hashes, and significance scores.

## Facts

- Endpoint: POST https://freshproof-api-mainnet.up.railway.app/v1/compare
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/freshproof-compare-c88f4dda
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_1Xo5jFFTCX8P-87Hi4K4e

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 freshproof-compare-c88f4dda -d '<json body>'
```

Example prompt: Check whether the Wikipedia page for 'Large language model' has changed since snapshot 3fa85f64-5717-4562-b3fc-2c963f66afa6 — tell me what facts are different, how significant the changes are, and show me the content hashes for both versions.

## When to prefer this

Choose this endpoint when you need a deterministic, evidence-backed diff between a live web page and a previously captured FreshProof snapshot. It is ideal for autonomous agents that must audit factual changes without hallucinating or inferring unsupported differences. Prefer it over generic scraping or summarization tools when reproducibility, content hashing, and verifiable evidence are required — especially for compliance, monitoring, or fact-checking workflows where provenance matters.

## Known failure modes

- Snapshot ID not found or expired — returns 404-equivalent with error indicating unknown snapshotId
- Target URL is unreachable or returns non-200 — returns error with retrieval failure details
- URL pattern validation failure if URL is malformed or non-HTTP/HTTPS
- Payment not included or insufficient — returns 402 Payment Required
- Rate limiting or timeout on the target URL causes partial or failed retrieval
- ProofBundle format mismatch causing comparison failure

## How this service works

Compare a fresh public web retrieval with previous evidence from a ProofBundle or retained snapshot. Returns deterministic fact differences, evidence, content hashes, retrieval timestamps, and significance for autonomous agents without inventing unsupported changes.

## Output

Returns a structured object containing deterministic fact differences (added, removed, or changed facts), content hashes for both the fresh retrieval and the previous snapshot, retrieval timestamps, evidence backing each difference, and a significance score indicating how materially the content has changed.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "url": {
   "type": "string",
   "pattern": "^https?://",
   "maxLength": 4096,
   "description": "Public HTTP or HTTPS URL to retrieve for fresh comparison."
  },
  "previous": {
   "type": "object",
   "required": [
    "snapshotId"
   ],
   "properties": {
    "snapshotId": {
     "type": "string",
     "pattern": "^([0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[1-8][0-9a-fA-F]{3}-[89abAB][0-9a-fA-F]{3}-[0-9a-fA-F]{12}|00000000-0000-0000-0000-000000000000|ffffffff-ffff-ffff-ffff-ffffffffffff)$",
     "description": "Identifier of a retained FreshProof snapshot."
    }
   },
   "description": "Previous evidence supplied as a ProofBundle or retained snapshot identifier.",
   "additionalProperties": false
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "changed": true,
  "warnings": [],
  "addedFacts": [],
  "currentHash": "bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb",
  "previousHash": "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
  "removedFacts": [],
  "modifiedFacts": [
   {
    "name": "price",
    "newValue": {
     "amount": 24.99,
     "currency": "USD"
    },
    "oldValue": {
     "amount": 19.99,
     "currency": "USD"
    },
    "newEvidence": {
     "quote": "USD 24.99",
     "locator": "Freshly retrieved product price evidence",
     "sourceUrl": "https://example.com/"
    },
    "oldEvidence": {
     "quote": "USD 19.99",
     "locator": "Previous retained product price evidence",
     "sourceUrl": "https://example.com/"
    },
    "significance": "material"
   }
  ],
  "currentSnapshotId": "8b267630-834b-46c8-8e70-b7ca7cc54e28",
  "currentRetrievedAt": "2026-07-28T08:30:00.000Z",
  "highestSignificance": "material",
  "previousRetrievedAt": "2026-07-27T08:30:00.000Z"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/freshproof-compare-c88f4dda/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from freshproof-api-mainnet.up.railway.app](https://www.zero.xyz/host/freshproof-api-mainnet.up.railway.app/llms.txt)