# URL Preflight Checker

> URL Preflight Checker is a paid API for AI agents from toolbelt402.tpoborne.workers.dev, paid per call via x402, $0.005/call, status unknown (last checked 2026-09-14).

Checks a URL before fetching it, returning liveness, final URL after redirects, HTTP status, content type, HTML title, and robots.txt accessibility for a given user-agent.

## Facts

- Endpoint: GET https://toolbelt402.tpoborne.workers.dev/url/preflight
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/url-preflight-checker-fe9975ee
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_RLSO9u4s15NVH--TjEFY8

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 url-preflight-checker-fe9975ee
```

Example prompt: Before I fetch https://example.com/some-article, can you preflight that URL and tell me if it's alive, what the final URL is after any redirects, the HTTP status, content type, HTML title, and whether robots.txt allows my user-agent 'MyBot/1.0'?

## When to prefer this

Choose this endpoint when an agent needs to safely preflight a URL before committing to a full fetch — especially useful for checking redirect chains, detecting dead links, verifying content type before parsing, and respecting robots.txt before crawling. Prefer it over a raw HTTP fetch when you want metadata without downloading the full body, or when you need robots.txt compliance checking as part of your workflow.

## Known failure modes

- Target URL is unreachable or times out — returns liveness false with no status
- Invalid or non-absolute URL provided — returns validation error
- robots.txt itself is unreachable — robots check may be inconclusive or default to allow
- URL resolves to a non-HTTP scheme — unsupported, likely returns error
- Redirect loop detected — may time out or return loop error

## How this service works

Check a URL before fetching it: is it alive, final URL after redirects, HTTP status, content type, HTML title, and whether robots.txt allows your user-agent. Link checker and fetch preflight for agents.

## Output

Returns whether the URL is alive, the final URL after following all redirects, the HTTP status code, the content-type header, the HTML page title, and a boolean indicating whether robots.txt permits the specified user-agent to access the resource.

## 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": [
      "url"
     ],
     "properties": {
      "ua": {
       "type": "string",
       "description": "User-agent to evaluate robots.txt against"
      },
      "url": {
       "type": "string",
       "description": "Absolute http(s) URL to check"
      }
     }
    }
   },
   "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/url-preflight-checker-fe9975ee/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from toolbelt402.tpoborne.workers.dev](https://www.zero.xyz/host/toolbelt402.tpoborne.workers.dev/llms.txt)