URL Health Check API
====================
Check HTTP status, redirect chains, SSL, soft-404 detection, and security
headers for any URL. No account required — get a free key at the payment page.

Endpoints
---------

GET /check?url=<URL>
  Check a single URL.

  Query params:
    url       (required) URL to check — must be http or https
    timeout   (optional) timeout in ms, default 10000, max 30000

  Response fields:
    reachable         false if connection failed or timed out
    status            HTTP status code of the final response
    finalUrl          URL after following all redirects
    urlChanged        true if URL changed during redirect
    responseTime      ms from request start to first byte
    redirectCount     number of redirects followed
    redirectChain[]   each hop: { url, status, location }
    softError.is404   true if page returned 200 but content signals "not found"
    ssl.enabled       true if final URL is HTTPS
    ssl.downgradedFromHttps  true if started HTTPS but ended up HTTP
    content           { type, charset, title, description, canonical, byteSize }
    headers           server, cache-control, last-modified, etag, security headers
    security          { missingHeaders[], score }  — score 0-100

POST /batch
  Check up to 10 URLs in parallel.
  Body: { "urls": ["https://..."], "timeout": 10000 }
  Response: { "count": N, "results": [...] }

Auth
----
Pass your API key via header (preferred) or query param:
  Header:  X-API-Key: <key>
  Param:   ?api_key=<key>

The response includes X-Credits-Remaining so you can track usage in code.

Examples
--------
  curl "https://api.michaelnovotny.dev/url-health/check?url=https://example.com" \
    -H "X-API-Key: YOUR_KEY"

  curl -X POST "https://api.michaelnovotny.dev/url-health/batch" \
    -H "Content-Type: application/json" \
    -H "X-API-Key: YOUR_KEY" \
    -d '{"urls":["https://example.com","https://httpbin.org/redirect/3"]}'