# HTTP Header Checker

> HTTP Header Checker is a paid API for AI agents from http-header-checker.underscoredone.com, paid per call via x402, $0.01/call, status unknown (last checked 2026-09-15).

Fetches and returns the HTTP response headers, status code, redirect chain, and missing security headers for any given URL

## Facts

- Endpoint: POST https://http-header-checker.underscoredone.com/check
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/http-header-checker-04c187ea
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_LGCLx_xzgUHhQ7_Pnu_4X

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 http-header-checker-04c187ea -d '<json body>'
```

Example prompt: Can you check the HTTP response headers for https://myblog.com — use a GET request and follow any redirects so I can see the final URL, status code, and any missing security headers?

## When to prefer this

Use this endpoint when you need to programmatically inspect HTTP response headers, status codes, redirect chains, or security header presence for any URL — especially useful for site audits, security checks, redirect debugging, or verifying CDN/cache configurations. Prefer this over a generic web scraper when you only need header metadata and not page content.

## Known failure modes

- Target URL is unreachable or times out — returns network error or timeout response
- Invalid URL format provided — returns validation error
- URL uses an unsupported scheme — returns error
- Domain does not resolve (DNS failure) — returns connection error
- Target server returns an unexpected non-HTTP response — may return partial or error result

## How this service works

Sends a request to a web address you provide and reports back everything the server said in response: the status code, all the response headers, how many times it got redirected, and how long the whole thing took.

## Output

Returns a JSON object containing the HTTP status code, all response headers as key-value pairs, the final URL after redirects, the full redirect chain with intermediate status codes, response time in milliseconds, and a list of missing security headers such as strict-transport-security and content-security-policy.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "url": {
   "type": "string",
   "description": "The full web address to check, including http:// or https://"
  },
  "method": {
   "type": "string",
   "description": "Either GET or HEAD; GET fetches the page normally, HEAD only asks for headers without the body"
  },
  "follow_redirects": {
   "type": "boolean",
   "description": "Whether to follow redirects to their final destination or stop at the first one"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "url": "https://example.com",
  "headers": {
   "server": "nginx",
   "content-type": "text/html; charset=UTF-8",
   "cache-control": "max-age=600",
   "content-length": "1256"
  },
  "final_url": "https://example.com/",
  "api_version": "1.0.0",
  "status_code": 200,
  "redirect_chain": [
   {
    "url": "http://example.com",
    "status_code": 301
   }
  ],
  "response_time_ms": 214,
  "missing_security_headers": [
   "strict-transport-security",
   "content-security-policy"
  ]
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/http-header-checker-04c187ea/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from http-header-checker.underscoredone.com](https://www.zero.xyz/host/http-header-checker.underscoredone.com/llms.txt)