Protocol Explorer

You type an address, hit Enter, and a page appears. Most of us can recite "DNS, then TCP, then TLS" in the right order, and most of us would struggle to say what's inside any of those packets. Textbook sequence diagrams don't help much. They show arrows, not bytes.

Protocol Explorer shows the bytes. Each lesson animates packets travelling between your laptop, the router, the ISP and servers across the internet, then decodes each one byte by byte, the way a packet analyzer like Wireshark would. You press play, watch a packet cross the map, and read what just happened and why the protocol was designed that way.

The footer sums up who it's for in one line: "Made for people who ask 'how does this work?'"

There are 39 protocols in the catalog, and every lesson follows the same step-by-step layout, so once you've done HTTP you know how to read the rest. Lessons come in eight languages, and your progress is saved in the browser.

The better half may be exam mode. After a lesson you switch from observing to building. Across 204 scenarios you draw the messages, connect the devices and check whether you can reconstruct the exchange yourself. That's much closer to what an interviewer or a certification exam asks of you than replaying an animation.

HTTP and HTTPS are free, lessons and exams both. A single $5 payment unlocks all 39 protocols for life, with no subscription or renewal. To buy it you sign in with Google and pay through Stripe. The terms call the unlock generally non-refundable and say you must be at least 13 to create an account.

According to the privacy policy, last updated November 2026, signing in shares your email and display name, card details stay with Stripe, and hosting and the database run on Cloudflare. Two things are worth knowing. No person or company is named anywhere on the site, only a contact email. And the policy mentions credit balances and subscription status, which don't match a product sold as a one-time unlock, so parts of it read like boilerplate. It gives no retention period either.

If you've ever nodded along to "the TLS handshake" without being sure what's in it, spend ten minutes with the free HTTPS lesson and see if it clicks.