About Circuit

Circuit is a free online C compiler and browser-based coding environment for learning, experimentation, and small programs. Its purpose is simple: give you a place to write C, run it, and return to your saved work without setting up an account or installing a desktop toolchain.

From an idea to a running program

The workspace brings together a syntax-highlighted editor, program tabs, and an interactive terminal. You can test a function, practice pointers, or step through the output of a loop. When a program asks for input, reply directly in the terminal and continue with the next question.

How it is built

The compiler uses LLVM Clang compiled to WebAssembly, distributed through YoWASP, with WASI libraries and a browser runtime. It executes in a Web Worker on your device. Circuit provides the surrounding workspace and program manager; it does not build a new C compiler or send your programs to a remote compilation service.

LLVM, Clang, WebAssembly, and the other third-party components belong to their respective projects; Circuit is not their official service.

Local by design

Programs are stored in your browser using IndexedDB. Export and import let you move your own backups between browsers or devices. There is no account-based synchronization, and browser storage is not a substitute for a backup.

Scope and limitations

The Learn C guides explain the language behind the workspace, and the examples library connects those ideas to complete, testable programs. The goal is to help you understand and check your own work, not merely copy an answer. See the documentation for actual features, storage behavior, and execution limits.

Circuit is intended for short, single-source C programs. It is not a full operating system, project build server, or production testing service. Some native libraries and operating-system APIs are unavailable. Execution and memory limits apply, and compatibility depends on your browser and device.

Open the online C compiler, read our Privacy Policy, or see Contact for feedback and support information.