Upload as index.html to the CDN bucket, then open the CDN URL. Everything below runs in your browser against this same origin.
Connection & TLS
CDN cache
Cloud CDN doesn't send an X-Cache header. A rising Age on repeat = served from edge cache. Age 0 = fill/miss.
Query-string cache key
Backend buckets include the full query string in the cache key, so each ?v= caches independently.
Compression
Browsers auto-decode and hide content-encoding, so this compares transfer vs decoded size from the Performance API.
Custom 404 / error page
If custom_error_responses = [{ match_response_codes=["404"], path="/404.html" }] is set and404.html exists in the bucket, you'll get its body with status 404. Otherwise the default GCS 404.
Raw response headers
Live fetch() of this page (same-origin, so all headers are readable).