Observe selected HTTP status codes
Observe how fixed success, redirect, client-error, and rate-limit statuses appear to a client.
Observe: Each allowlisted choice returns its fixed status and bounded representation.
Observe controlled HTTP behavior
Predict a result, run one allowlisted request, and connect the observation to the protocol rule. Every lesson remains readable without JavaScript or the Worker.
Read responses
Observe compression negotiation
Observe how Accept-Encoding, Content-Encoding, and Vary participate in one bounded response.
Observe: The fixed response selects identity or gzip from supported request preferences.
Follow request flow
Compare methods across redirects
Compare historical method rewriting with explicit method-preserving redirect semantics.
Observe: Fixed 301 and 302 paths can demonstrate permitted historical POST-to-GET behavior.
Follow a bounded redirect chain
Observe that a redirect chain is a sequence of separate exchanges, not one response.
Observe: Each fixed hop has its own status and relative Location value.
Observe a CORS preflight
Observe how a browser asks permission for a method and fields before sending the intended request.
Observe: The safelisted request proceeds without an OPTIONS preflight.
Understand reuse
Observe cache freshness
Observe the difference between a fresh stored response and one that requires another cache decision.
Observe: The fixed representation has an explicit short freshness lifetime.
Observe ETag revalidation
Observe how If-None-Match can validate a stored representation without retransmitting it.
Observe: An unconditional request returns a fixed representation and entity tag.
Safety boundary
Controlled scenarios only
The Lab never accepts an arbitrary destination, credential, script, or unbounded body. Cookie scope remains a static draft until a same-site production origin can be verified; this preview makes no cross-site claim.