Does this tool perform live network packet capture?

No, this is an offline reference tool built directly from RFC 9000 and RFC 9114 specifications.

What is the difference between 1-RTT and 0-RTT scenarios in QUIC?

1-RTT requires one round trip to establish keys, while 0-RTT uses a cached session ticket to send application data in the first flight.

Why does the Retry packet not carry application data?

The Retry packet is strictly used by the server for address validation to prevent denial-of-service attacks.

How does QUIC prevent head-of-line blocking compared to TCP?

QUIC multiplexes streams natively over UDP, meaning packet loss on one stream does not block data delivery on other streams.

What fields are shown in the detailed byte-level layout?

It displays long-header flags, version, DCID/SCID, lengths, packet numbers, and the CRYPTO frame payload.

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HTTP/3 QUIC Handshake Anatomy

Dissect the HTTP/3 over QUIC handshake byte-by-byte. Visualise the 1-RTT fresh handshake, session-ticket resumption, and 0-RTT early-data scenarios, with sequence diagrams, per-packet field layouts, the Retry packet, and a side-by-side comparison against TCP + TLS 1.3. Built for interview prep, protocol learning, and performance engineering.

Details

What this tool helps you do

A byte-level anatomy of the HTTP/3 over QUIC handshake for network engineers, SREs and learners:

Pick a scenario: a fresh 1-RTT connection, a resumed connection using a session ticket, or 0-RTT early data.
The sequence diagram shows each flight (Initial, Handshake, 1-RTT) grouped by round trip, with direction arrows and packet/ frame badges.
Detailed mode adds byte-level field layouts for every QUIC packet: long-header flags, version, DCID/SCID, lengths, packet number and the CRYPTO payload.
The Retry explainer covers address validation: the token the server issues, the integrity tag, and why Retry never carries application data.
The comparison table contrasts QUIC/HTTP-3 against TCP + TLS 1.3 across merged handshakes, time to first byte, head-of-line blocking, connection migration and middlebox maturity.

Offline reference: built from RFC 9000 (QUIC) and RFC 9114 (HTTP/3); no live capture is performed.

Execution

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Prepared example runs

Click an example to fill the form automatically. File inputs still need an upload.

2 examples

Fresh 1-RTT HTTP/3 handshake

A first-time connection showing the integrated QUIC+TLS handshake and where the first HTTP/3 request is sent after a single round trip.

<div class="qh-wrap">…hero, sequence with Initial/Handshake/1-RTT packets, byte-level cards, Retry packet map, and the TCP+TLS comparison table…</div>

0-RTT early data scenario

A resumed connection where the client sends application data in its very first flight using a cached PSK, highlighting replay risks.

<div class="qh-wrap">…0-RTT hero and sequence with early-data flight, server acceptance, and key facts stressing replay protection…</div>

Inputs

Set the required fields, then run the tool.

4 options

SettingsAdjust formats, ranges, numbers, and modes.2

Handshake scenarioselectOptionalDetail levelselectOptional

TogglesEnable or disable optional behavior.2

Show comparison vs TCP + TLS 1.3checkboxOptionalEnabled when checkedShow QUIC long-header byte mapcheckboxOptionalEnabled when checked

Result

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Samples

HTTP/3 QUIC Handshake Anatomy

What this tool helps you do

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Key facts

Overview

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How it works

Use cases

Examples

1. Analyzing 0-RTT Early Data Replay Risks

2. Deep Dive into Fresh 1-RTT Handshake Fields

FAQ

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