Cloudflare ended 2024 by announcing a new open source project: h3i for HTTP/3 low-level testing and debugging. Cloudflare's new open source h3i project is a command line tool and Rust library for low-level testing and debugging of HTTP/3. The h3i freeware is part of Cloudflare's larger Quiche project.

The h3i tool allows for quick low-level debugging and exploratory testing around HTTP/3. In its simple form, the h3i tool is similar to the curl command line tool, but with the addition of HTTP/3 parameters. h3i supports recording and replay, sending intentionally malformed requests using Rust, built-in test automation, and other features.

"Cloudflare takes testing very seriously. While h3i has limited functionality as a test HTTP/3 client, we believe it provides a powerful framework that can be extended to a wider range of different situations and different protocols. For example, we hope to add support for underlying HTTP/2.

We designed h3i to be integrated into a variety of testing methods, from manual ad-hoc testing to native Rust testing to conformance testing platforms built using scripting languages. We have successfully migrated our existing testing tools into a single tool that is easier to access and maintain. "

Users wishing to learn more about the h3i open source project can do so via the Cloudflare blog. Code is available via the QuicheGitHub repository.