I built a code runner for 14 languages - try to break it and test

Vojtěch Mikle — Wed, 27 May 2026 17:17:51 +0000

I wanted a fast way to test code snippets without opening an IDE or spinning up a repl. So I built simplelanguages.com.

You pick a language, type code, hit Ctrl+Enter. The backend compiles and runs it, sends back stdout/stderr/exit code/timing.

What it runs:

python, javascript, typescript, java, c, c++, c#, rust, lua, go, ruby, php, html, css

What's there:

Dark terminal UI, works on mobile
Web mode for HTML/CSS/JS with live iframe preview (renders client-side, no API call)
6 themes (Nord, Dracula, Monokai, CRT green, amber, solar flare)
Community plugin system — anyone can submit plugins, I approve them
Shareable URLs (code + language base64'd into the hash)
Ctrl+Enter to run, Ctrl+F for find/zen mode, Ctrl+Shift+S to copy share link

Stack:

Backend is Rust/Axum — receives code, spawns a process in a temp directory, kills it after 30 seconds if it hangs. Frontend is vanilla JS with CodeMirror 6, no framework. Hosted on GitHub Pages, backend on Render free tier.

Why I'm posting:

I've been staring at this for weeks and I'm blind to its flaws. I know things are broken, I just can't see them anymore.

If you've got a few minutes, open it up and try to break something. Weird edge cases, things that feel off, layout breaking on your phone, whatever. Don't tell me what's good - tell me what sucks.

https://rodancz.github.io/simplelanguages/

https://github.com/rodancz/simplelanguages

(Backend sleeps after 15min of inactivity on Render's free tier - first request takes about 30 seconds to wake it. Just wait, it'll load.)

Forem: Vojtěch Mikle

I built a code runner for 14 languages - try to break it and test