Home/Free tools
// Free tools
Free online compilers that run in your browser
Ten languages, each on a real compiler that downloads into your own tab - no signup, no upload, no queue behind other people's jobs. Every runner on this page executes in your own browser tab. Your code is never uploaded, never queued behind anyone else, and never stored anywhere but your own browser.
A real analytical SQL database, close to PostgreSQL, running in your tab. It is the same engine the graded SQL practice runs on.
Open the SQL compiler →PythonThe standard Python 3.14 interpreter, running in your tab. Not a subset and not a transpiler - the same Python you run on your own machine.
Open the Python compiler →JavaScriptA complete ES2023 JavaScript engine, sandboxed away from the page. It is served with this page rather than from another site, so the first run starts almost at once.
Open the JavaScript compiler →TypeScriptThe TypeScript 6.0 compiler typechecks your code, then a sandboxed engine runs the JavaScript it emits. Type errors are the compiler's own, word for word.
Open the TypeScript compiler →JavaA real Java compiler, running in your tab. It compiles your class into a program that then runs right there in the tab.
Open the Java compiler →C#The real C# compiler on the .NET 10 runtime - your code is compiled to IL and executed, in the tab.
Open the C# compiler →C++A real C++20 compiler and linker, running in your tab. Your program is compiled and linked into a real binary there, then executed.
Open the C++ compiler →CA real C17 compiler and linker, running in your tab, with the undefined-behavior sanitizer on. Read past the end of an array or overflow a signed int and the program stops on that line and says so.
Open the C compiler →GoThe real Go 1.27 compiler and linker, running in your tab. Your program is compiled and linked into a binary there and then executed - it is not interpreted and it is not a translation of Go into something else.
Open the Go compiler →RubyReal Ruby 3.4 - the reference interpreter - running in your tab. Not a subset and not a translation into JavaScript.
Open the Ruby compiler →Nothing you type is sent to a server. Your code is saved only in this browser, the engine is downloaded once and cached, and once it has loaded the page keeps running your code with the network off.
// How this works
The compiler comes to you
An online compiler normally means a server: your code is uploaded, queued, run in a container with a time limit, and the output is sent back. Every one of these tools inverts that. The compiler itself comes to your browser, which downloads it once and then does the work - which is why there is no account, no rate limit and nothing to store.
What that buys you
- Your code stays on your machine. Nothing is uploaded, logged or kept.
- No queue and no rate limit: the only machine involved is yours.
- Once the engine has loaded, the page keeps working with the network off.
What it costs you
- A one-time download per language, the first time you press Run. Your browser keeps it afterwards.
- No network, no filesystem and no threads inside the sandbox.
- A few seconds of wall clock per run, which is the ceiling that stops a runaway loop.
// The engines
Real compilers, not simulators
These are the same engines that grade the practice on Prepshotz, which is the only reason ten of them exist. Nothing here is a reimplementation of a language: each one is the real compiler, interpreter or database, running in your tab.
// Questions
Free online compilers - FAQ
01Which languages can I run here?
Ten: SQL, Python, JavaScript, TypeScript, Java, C#, C++, C, Go and Ruby. Each one runs on its own real compiler, interpreter or database, right in your browser.
02Do these really run in my browser?
Yes. Each compiler is downloaded to your browser the first time you press Run, then cached. Your code is compiled and executed on your own machine, so there is no upload, no queue and no per-run cost to us. That is why it is free with no account.
03Is my code uploaded or stored?
No. The compiler comes to your code rather than the other way round, so nothing you type is sent to a server, logged or stored. Closing the tab is the whole of the cleanup.
04What is the catch?
There is no catch and no upsell in the tools themselves. They exist because Prepshotz already runs these ten engines in the browser for its graded practice, so offering them on their own costs us nothing per run. If you want the graded version - real problems, real test cases, a track that adapts to what you keep missing - that is the product, and it is free while we are in beta too.