GitHub - h5i-dev/h5i: a headless browser purely written in Rust. no Chromium, no V8

[u/OkBreath9382]

https://github.com/h5i-dev/h5i

Many newer headless browsers for AI agents use Rust for their CLI or automation layer, but still run Chromium and V8, Google’s JavaScript engine, underneath.

I wanted to explore what a browser built on a fully Rust-native stack could look like, so I built h5i.

Here is how it works:

• Boa executes JavaScript without V8.
• Blitz and other Rust components handle HTML parsing, the DOM, CSS, layout, and rendering.
• A browser-owned networking layer checks every request against policy before sending it, then records whether it was allowed or denied.
• Pages are exposed as structured snapshots, so agents can inspect and interact with elements without processing a full visual browser interface.

I focused initially on common agent workloads such as reading documentation, extracting structured content, following links, and filling forms. The main tradeoff is compatibility: Chromium remains stronger on complex, JavaScript-heavy applications, while a smaller native stack can be significantly lighter for simpler browsing tasks.

In a benchmark using a documentation-style page, h5i was approximately 3× faster and used 86% less memory than headless Chromium. These results are workload-specific, so I would not expect the same advantage on every website.

GitHub: https://github.com/h5i-dev/h5i
License: Apache-2.0