Rust Online Compiler | Free Online Compiler

Code

fn main() {
    println!("Hello, Rust!");
}

STDIN (optional)

Args (space separated)

Output

What Is the Rust Online Compiler?

This tool lets you compile and run Rust programs directly in your browser without installing the Rust toolchain on your machine. Whether you are learning Rust for the first time or quickly testing ownership and borrowing concepts, this compiler provides a fast way to write and execute Rust code online.

Your code must include a fn main() entry point, which is the standard starting function for Rust programs. You can use the println! macro to print output, along with other standard library features like iterators, pattern matching, and error handling with Result and Option.

All code executes on a remote sandboxed server powered by the Piston API. Your browser sends the source code to the server, which compiles it with rustc and runs the resulting binary inside an isolated container. Rust's memory safety features, including ownership, borrowing, and lifetime checks, are fully enforced during compilation.

How It Works

Write your Rust code in the editor panel. The editor starts with a simple "Hello, Rust!" example using fn main(), but you can replace it with any valid Rust program.
Provide input in the STDIN field if your program reads from standard input using std::io::stdin() or read_line. Leave this field empty if your program does not require input.
Add command-line arguments in the Args field if your program reads from std::env::args(). Enter arguments separated by spaces.
Click the Run button to send your code to the Piston execution server. The server first compiles your Rust source code with rustc, then executes the resulting binary and captures all output.
View the results in the Output panel. You will see everything your program prints to standard output, along with any compiler errors including borrow checker violations, type mismatches, or runtime panics.

Step-by-Step Example

Suppose you want to write a program that reads a name from standard input and prints a greeting using pattern matching. Here is how you would do it using this compiler:

First, type the following code into the editor panel:

use std::io;

fn main() {
    let greeting = String::from("Hello");
    let mut name = String::new();

    io::stdin()
        .read_line(&mut name)
        .expect("Failed to read line");

    let name = name.trim();

    match name.is_empty() {
        true  => println!("{}, stranger!", greeting),
        false => println!("{}, {}!", greeting, name),
    }
}

This example demonstrates several Rust features: let bindings for variable declaration, String for heap-allocated text, read_line for reading from stdin, and pattern matching with match.

Next, go to the STDIN field and type a name, for example Alice. This value will be read by read_line when the program runs.

Now click the Run button. The compiler first builds your Rust source code with rustc, then executes it with the provided input. After a moment, the Output panel displays the result:

Hello, Alice!

If you leave the STDIN field empty and click Run again, the output changes to show the fallback branch of the match expression. This workflow makes it easy to test different inputs and observe how pattern matching behaves.

Use Cases

Learning Rust fundamentals. Beginners can experiment with variables, ownership, borrowing, lifetimes, structs, enums, and traits in a zero-setup environment.
Testing ownership and borrowing rules. Quickly verify how the borrow checker responds to mutable references, moves, and lifetime annotations without a local Rust installation.
Practicing algorithms and data structures. Implement sorting algorithms, tree traversals, graph searches, and other common problems using Rust's standard collections like Vec, HashMap, and BTreeMap.
Exploring error handling patterns. Experiment with Result, Option, the ? operator, and match expressions to understand how Rust handles recoverable and unrecoverable errors.
Preparing for coding interviews. Many interview questions can be solved in Rust. Use this compiler to practice problems, test edge cases, and refine solutions quickly.

Limitations and Notes

Single file execution only. This compiler runs a single Rust file (main.rs). Multi-file projects and separate modules in different files are not supported.
No Cargo support. The Cargo build system and package manager are not available. You cannot use Cargo.toml or build scripts.
No crates.io dependencies. External crates from crates.io cannot be imported. Only the Rust standard library (std) is available.
Standard library is available. You can use modules like std::io, std::collections, std::fmt, std::fs (limited), and other standard library features.
No file I/O access. The sandboxed environment does not allow reading from or writing to the filesystem. File operations will fail at runtime.
Execution timeout applies. Programs that take too long or enter infinite loops are terminated automatically to prevent resource exhaustion.
Unsafe blocks have limitations. While unsafe syntax is accepted by the compiler, certain low-level operations may be restricted by the sandboxed execution environment.

Frequently Asked Questions

What Rust version does this compiler use?

It uses the latest stable Rust version provided by the Piston execution engine.

Can I use the standard library?

Yes, the std crate is fully available including collections, io, fmt, and other standard modules.

Can I use external crates?

No, there is no Cargo or crates.io support. Only the standard library is available.

Does the borrow checker work?

Yes, the full Rust compiler runs including the borrow checker. You will see ownership and lifetime errors just like in a local environment.

Can I use stdin?

Yes, use std::io::stdin() to read input. Provide your input data in the STDIN field before running.

Is there a compilation step?

Yes, rustc compiles your code first. You will see compiler errors for type mismatches, borrow violations, and syntax issues before execution.

Can I use async/await?

Basic async syntax works but no async runtime such as tokio or async-std is available. You would need to poll futures manually.

Does this support macros?

Yes, standard macros like println!, vec!, format!, assert!, and other built-in macros all work as expected.

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