Product
Rust Online
Rust Online is a browser Rust editor with a streaming AI companion, span-level compiler error explanations with suggested fixes, plain-English error mode, and server-side compile caching.
- Started
- August 2026
- Status
- Live
- Signal
- Developer tool
The question
How much of a Rust workflow can you get without installing anything, and can the errors stop being the hard part?
Rust has a setup cost: toolchain, cargo, a project layout, a first compile that is slow. Then it has a second cost that nobody warns you about, which is reading the output when the borrow checker disagrees with you.
Context
Most people trying a snippet are not starting a project. They want to check how ownership behaves in a case they are unsure about, run one test, or show someone what a piece of code does. The blocker is rarely the editor. It is the wall of compiler text between the attempt and the understanding.
What it does now
AI companion. Ask about the code in the buffer and the answer streams back word by word, so you start reading before the model finishes.
Errors tied to the exact span. When rustc points at a range, the editor underlines that range and attaches a suggested fix, instead of leaving you to count line and column numbers.
Two ways to read an error. A toggle switches between the raw rustc output and a plain-English explanation of the same diagnostic. The raw text is never replaced, only folded away.
A composer built for the loop. Type / for commands, @ to pull in context from the file, and hit stop when a response is going the wrong way.
Honest feedback while you wait. A loader with a live timer, and a status chip that says whether the run was compiled, served from cache, or skipped.
Server-side compile caching. Identical snippets do not get recompiled. Repeat runs come back immediately, which is most runs when you are iterating on one function.
What I learned
The editor was never the interesting part. The feedback loop is. Two things moved the needle more than anything else: cutting the wait on repeat compiles so the loop feels closer to instant, and keeping the raw compiler output visible next to the explanation. Hiding rustc entirely would teach people to depend on the tool. Showing both teaches them to read the real thing.