Kotlin Code Formatter
Format and beautify Kotlin source code — re-indent by brace depth, normalize operator and comma spacing, sort imports, and add trailing commas to multi-line lists. Runs entirely in your browser.
Input
Formatting Options
Output
Guides
The Kotlin Code Formatter cleans up messy, minified, or inconsistently indented Kotlin source into readable, ktlint-style code. Paste a snippet or upload a .kt file, pick your options, and get properly indented output with normalized spacing — instantly, without installing Gradle, the Kotlin compiler, or an IDE plugin.
It is built for the quick cases where reaching for a full toolchain is overkill: tidying a Stack Overflow answer, cleaning a code-review paste, formatting a gist, or making a compressed snippet legible before you study it.
How to use it
- Paste your Kotlin code into the input box, or upload a
.ktfile. - Choose an Indent Size — 2 spaces, 4 spaces, or tabs.
- Toggle Sort imports alphabetically and Add trailing commas in multi-line lists to taste.
- The formatted result appears on the right, ready to copy or download as
formatted.kt.
Formatting runs as you type, so you can tweak options and watch the output update live.
What it does
- Re-indents every line by brace, parenthesis, and bracket nesting depth, so
fun,class,object,interface,if/else,when,for,while, andtry/catch/finallyblocks line up correctly. - Normalizes spacing around operators (
=,==,&&,||,?:,->), after commas and colons, and inserts a space after control-flow keywords before their parenthesis (if(x)becomesif (x)). - Preserves strings and comments untouched — string templates like
"$name"and"${user.id}", triple-quoted raw strings, line comments, and nested KDoc block comments are recognized so their contents are never re-spaced or re-indented. - Sorts consecutive import lines alphabetically (optional).
- Adds trailing commas to multi-line parenthesized and bracketed lists (optional), matching modern Kotlin style.
Does it check my code for errors?
No. This is a formatter, not a compiler. It re-lays-out whatever you give it and does not report syntax errors or change program behavior. Invalid Kotlin is reformatted as best it can, but it is not validated.
Is it a full replacement for ktlint or the IntelliJ formatter?
Think of it as a fast, zero-setup cleanup pass. It handles indentation and spacing — the things that make a paste unreadable — but it does not wrap long lines, reorganize declarations, or enforce every ktlint rule. For a canonical, project-wide style, keep using ktlint or your IDE in your build.
Can I format a whole file?
Yes. Use the file uploader to load a .kt file, format it, and download the result. There is no practical size limit for typical source files.
Which Kotlin features are supported?
Standard Kotlin syntax: functions, classes, objects, interfaces, data classes, sealed classes, enums, when expressions, lambdas and trailing-lambda blocks, string templates, and raw strings.
Privacy
This tool runs entirely in your browser. Your code is never uploaded to a server — formatting happens locally in JavaScript, so even proprietary or sensitive source stays on your own machine.
Use it from code
From 3 credits per callREST API
curl -X POST https://api.iotools.cloud/v1/tool/kotlin-code-formatter \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"kotlinInput": "fun greet(name:String):String{\nif(name.isEmpty()…",
"indent": "4",
"sortImports": "true",
"trailingCommas": "true"
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `kotlin-code-formatter` tool (Kotlin Code Formatter) on this input:
YOUR_INPUT_HEREPaste this at any agent connected to the IOTools MCP server, then add your input.