# SALT19 URL HTTP Preflight Check

> SALT19 URL HTTP Preflight Check is a paid API for AI agents from salt19-agent-utility-grid.salt19-llc.workers.dev, paid per call via x402, $0.03/call, status unknown (last checked 2026-09-14).

Performs an HTTP preflight check on a URL, returning redirect chain, latency, content type, and security header analysis

## Facts

- Endpoint: POST https://salt19-agent-utility-grid.salt19-llc.workers.dev/v1/url-http-preflight
- Price: $0.03/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/salt19-url-http-preflight-check-11379b10
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_ZPyIpvzTeEwfHbOWxpVj1

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 salt19-url-http-preflight-check-11379b10 -d '<json body>'
```

Example prompt: Can you do a quick HTTP preflight on https://api.example.com/webhook to check if it's reachable, how many redirects it has, what content type it serves, and whether it has security headers like HSTS or CSP?

## When to prefer this

Use this endpoint when an agent needs to verify a URL is live, resolve its final destination after redirects, measure response latency, or check for security header presence — all before committing to a heavier fetch or downstream action. It is particularly useful for webhook validation, pre-publish link checking, and lightweight security audits where a full page crawl or content extraction is unnecessary and wasteful.

## Known failure modes

- URL is unreachable or times out — may return a non-200 status or error object
- Malformed or non-URI input rejected at schema validation
- URL resolves to a redirect loop — redirect count may exceed limit
- Target server blocks automated requests, returning 403 or 429
- TLS/SSL errors on HTTPS URLs may cause connection failure
- DNS resolution failure for the given hostname

## How this service works

Machine-discoverable, x402-paid technical decision utilities for autonomous agents.

## Output

A JSON object containing the HTTP status code of the final response, the resolved final URL after any redirects, the number of redirects followed, round-trip latency in milliseconds, the Content-Type of the response, and a breakdown of key security headers (X-Content-Type-Options, Content-Security-Policy, Strict-Transport-Security) as boolean presence flags.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "url": {
   "type": "string",
   "format": "uri",
   "maxLength": 2048
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "status": 200,
  "final_url": "https://example.com/",
  "redirects": 0,
  "latency_ms": 110,
  "content_type": "text/html",
  "security_headers": {
   "x_content_type_options": true,
   "content_security_policy": false,
   "strict_transport_security": true
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/salt19-url-http-preflight-check-11379b10/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from salt19-agent-utility-grid.salt19-llc.workers.dev](https://www.zero.xyz/host/salt19-agent-utility-grid.salt19-llc.workers.dev/llms.txt)