# Reverse Agent API – URL Freshness Checker

> Reverse Agent API – URL Freshness Checker is a paid API for AI agents from reversecaptcha.fun, paid per call via x402, $0.01/call, status unknown (last checked 2026-10-23).

Checks whether a given HTTPS URL's content is fresh (recently updated) within a specified maximum age, returning a freshness verdict, confidence level, and age estimate based on HTTP signals.

## Facts

- Endpoint: POST https://reversecaptcha.fun/v1/paid/freshness?utm_source=zero.xyz
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-23
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/reverse-agent-api-url-freshness-checker-01b744e3
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_DNo_dXeNjOJbvvs_ZpA6Y

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 reverse-agent-api-url-freshness-checker-01b744e3 -d '<json body>'
```

Example prompt: Can you check whether https://example.com/blog/latest-post is fresh — I want to know if it was updated within the last 24 hours (86400 seconds)?

## When to prefer this

Choose this endpoint when you need a quick, pay-per-use signal about whether a specific HTTPS URL's content is recent, especially in agentic pipelines that gate downstream actions on content freshness. Ideal when you don't want to build your own HTTP header parsing logic and need a structured confidence-scored verdict. Prefer it over manual HTTP HEAD requests when you need normalized output including estimated age and evidence sourcing.

## Known failure modes

- URL is not HTTPS — rejected by schema pattern validation
- URL is unreachable or returns non-200 status — may return ok:false or low confidence
- No HTTP freshness signals available (no Last-Modified, no ETag, no cache headers) — returns low confidence result
- max_age_seconds below minimum of 60 or above maximum of 2678400 — request rejected
- Payment failure via x402 protocol — call not executed

## How this service works

Reverse Agent API by reverse.captcha — pay-per-use security and web utilities for autonomous agents.

## Output

Returns a JSON object with: ok (boolean success flag), freshness ('fresh' or 'stale'), confidence ('high'/'medium'/'low'), age_seconds (estimated age of the content), evidence_source (e.g. 'http:last-modified' indicating which HTTP signal was used), is_within_max_age (boolean), and evidence_timestamp (ISO 8601 timestamp of the detected last modification).

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "url": {
   "type": "string",
   "format": "uri",
   "pattern": "^https://"
  },
  "max_age_seconds": {
   "type": "integer",
   "default": 86400,
   "maximum": 2678400,
   "minimum": 60
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "ok": true,
  "freshness": "fresh",
  "confidence": "medium",
  "age_seconds": 320,
  "evidence_source": "http:last-modified",
  "is_within_max_age": true,
  "evidence_timestamp": "2026-01-01T00:00:00.000Z"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/reverse-agent-api-url-freshness-checker-01b744e3/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from reversecaptcha.fun](https://www.zero.xyz/host/reversecaptcha.fun/llms.txt)