Try the free tool below. It runs in your browser, with no sign-up and no download.
What Is the YAML Formatter and Validator?
YAML is a plain-text format used for settings files, automation rules, and app configuration. It is easy to read, but it is strict about spaces: one wrong indent can break a whole file. Our YAML formatter and validator checks your YAML and rewrites it in a clean, even layout, so you can spot mistakes fast and share a tidy file.
The tool uses js-yaml, a well-known YAML library, and everything runs in your browser. Your text never leaves your device, which matters when a settings file holds server names, project details, or other private values. Paste, format, and copy the result.
How to Use It
Paste your YAML into the box and press Format. The tool reads the text, and if it is valid, it prints it back with two-space indents, one item per line, and lists laid out clearly. If it is not valid, the tool shows the error message from the parser, which usually points at the line and the problem, such as a bad indent or a stray tab.
Press Validate when you only want a yes-or-no answer without changing your text. That is useful before you save a file or paste it into a server, because a quick check now can save a failed deploy later.
Common YAML Mistakes
The most common mistake is mixing tabs and spaces. YAML forbids tabs for indentation, so use spaces only. The next most common is uneven indentation: items under one key must line up exactly. A third common mistake is an unquoted value that looks like something else, such as yes, no, or a date, which YAML may read as a boolean or a date instead of plain text.
Quoting values that could be misread is a good habit. If a value starts with a special character, contains a colon followed by a space, or looks like a number you want to keep as text, wrap it in quotes.
Who Is It For?
This tool suits developers editing GitHub Actions workflows, Docker Compose files, Kubernetes settings, and app configs. It also suits students learning YAML and anyone who received a broken settings file and needs to find the fault quickly.
Because it works offline in your browser once the page loads, you can use it on a plane, in a meeting, or on a machine where you cannot install software.
Frequently Asked Questions
Is my YAML sent to a server? No. The check and the formatting run in your browser.
What does the formatter change? It rewrites spacing and layout. It keeps your keys, values, and structure the same.
Why does my file fail with a tab error? YAML does not allow tabs for indentation. Replace tabs with spaces.
Can I download the result? Yes. The download button saves the formatted text as a .yaml file.
A Worked Example: Fixing a Broken File
Imagine a settings file that fails with a vague error. The first step is to paste it into the validator and read the exact message, which often names a line number. Go to that line and check the indentation of every line around it, counting spaces carefully. A common culprit is a list item that sits one space too far left or right, which changes which key it belongs to. Another is a line that mixes a tab with spaces, which looks fine on screen but breaks the parser. Fix the spacing, validate again, and repeat until the message clears. Then press Format to rewrite the file cleanly, and compare the formatted version with your original to see what changed. This loop of validate, fix, and format again is the standard way professionals clean up YAML, and it works just as well for a ten-line file as for a thousand-line one. Keep the formatted version as your saved file, because its even layout makes the next edit easier and less error-prone.
One more habit helps: validate after every small edit, not only at the end. Catching a mistake right after you make it takes seconds, while hunting it later in a long file can take far longer.
Also in Spanish
This tool is also available in Spanish: Formatear y Validar YAML Gratis – Ordena y Revisa tu YAML.