Staaarter Tools

Rust Formatter

Paste Rust code and get back a reindented version based on brace nesting depth. This is a lightweight structural reindenter, not a full formatter like rustfmt, which requires the Rust toolchain. A free online tool from Staaarter, right in your browser.

Runs locallyUpdated 2026-07-24
formattingrust

Overview

Introduction

Rust code pasted from documentation or a non-rustfmt-formatted source often has indentation that doesn't match its brace structure.

This tool reindents each line based on `{ }` nesting depth, entirely in your browser, without requiring the Rust toolchain.

What Is Rust Formatter?

A lightweight reindenter that tracks brace, parenthesis, and bracket depth line by line and re-indents accordingly.

It's a whitespace-only pass: tokens and logic are never touched, only leading indentation.

How Rust Formatter Works

Each line is scanned for `{}/()/[]` characters to compute a running nesting depth.

Lines that start with a closing brace are dedented one level before printing, matching their opening brace.

When To Use Rust Formatter

Use it when a Rust snippet's indentation has drifted after manual edits.

It's a quick visual check that braces are balanced.

Often used alongside C Formatter, Go Formatter and Java Formatter.

Features

Advantages

  • Runs entirely client-side with no Rust toolchain required.
  • Fixes indentation drift instantly for typical brace-delimited code.
  • Handles arbitrarily deep nesting without any configuration needed.

Limitations

  • Not a real parser: brace characters inside string literals, lifetimes, or comments still affect depth.
  • For rigorous style enforcement, use `rustfmt` locally, which the Rust community expects verbatim.

Examples

Drifted indentation

Input

fn greet(name: &str) -> String {
format!("Hello, {}", name)
}

Output

fn greet(name: &str) -> String {
    format!("Hello, {}", name)
}

Content inside the function body indents one level deeper, matching the opening brace.

Best Practices & Notes

Best Practices

  • Use this only for a quick visual cleanup; always run the real `rustfmt` before committing Rust code.
  • Check whether the final line's indentation returns to depth zero, that's a quick sign no closing brace is missing.

Developer Notes

Implemented as a single-pass line scanner that tracks a running brace/paren/bracket balance; it does not tokenize strings, lifetimes, or comments.

Rust Formatter Use Cases

  • Quickly cleaning up indentation in a pasted Rust snippet before running rustfmt
  • Spotting an unbalanced brace by eye

Common Mistakes

  • Committing this tool's output directly instead of running it through the real `rustfmt`.
  • Assuming brace characters inside string literals, macros, or comments are ignored, they aren't; the scanner counts every `{`, `}`, `(`, `)`, `[`, or `]` regardless of context.

Tips

  • Always pipe the final code through `rustfmt` locally; this tool is a stopgap for quick browser-based cleanup, not a replacement.
  • Diff the reindented output against your original before running rustfmt, so you can see exactly which lines shifted.

References

Frequently Asked Questions