Format, validate and inspect YAML without losing a single comment.
100% client-side — your config never leaves your browser.
Validation answers whether a parser will accept the file. The Lint tab covers what parses cleanly but will not mean what you intended.
Most online YAML formatters are built on js-yaml, which parses your file into a plain object and throws the rest away. Format a commented Kubernetes manifest with one and every `#` explaining why a value is what it is disappears. This one is built on the yaml package's document model, so comments, anchors, aliases and key order all survive the round trip — and everything runs in your browser, so the config never leaves your machine.
Header comments, inline notes, anchors, aliases and merge keys come out the other side exactly as you wrote them. This is the single biggest gap in the online YAML tools that rank today, and the reason people give up and paste into an editor instead.
Valid YAML can still be wrong. The tool flags unquoted no/yes/on/off (the Norway problem), duplicate keys that silently discard your earlier value, version numbers like 1.10 that collapse to 1.1, file modes like 0755 that lose their leading zero, and IDs too long to survive as floats. No other online formatter checks any of this.
Set 2, 4 or 8 spaces, and choose whether sequence items indent under their key or sit flush against it — the one YAML style argument that actually divides Kubernetes and Ansible codebases. Expand inline flow collections to block style, sort keys for stable diffs, or leave the order exactly as authored.
Kubernetes manifests are almost always several documents separated by ---. Each one is parsed, validated and formatted independently, and the separators stay where they belong instead of collapsing into a single broken document.
Turn YAML into JSON, paste JSON to get YAML back, or collapse the whole document to compact flow style when you need it on one line. Aliases are resolved on conversion so the JSON is complete.
Parsing, formatting, linting and conversion are JavaScript running in your tab. There is no backend, so there is no file-size cap and no copy of your secrets sitting in someone's logs. It keeps working with the network off.
No signup, no install, no plugin. It works the same on desktop and mobile.
Paste it into the editor, press Open File to pick a .yaml, .yml, .k8s or Compose file from your device, or drag one onto the workspace. Large files are fine — there is no server, so there is no upload limit.
Syntax problems appear with an exact line and column and a plain-English cause. The Lint tab separately lists the things that parse fine but will bite you later, each with the fix.
Choose indent width, sequence indentation, key sorting and flow expansion, then press Format. Your comments and anchors stay put. Minify collapses the document to flow style when you need it compact.
Copy the result, switch to the Convert tab for JSON, or download it as a file. Your settings and last document are remembered locally, so the page opens the way you left it.
A formatter that drops comments is not formatting, it is rewriting. Because this one works on the document tree rather than a parsed object, the only thing that changes is whitespace and the style options you deliberately chose.
Every experienced engineer has been bitten by a country code turning into false, a duplicate key silently winning, or a version string losing its trailing zero. These parse cleanly, so a validator will never mention them. The lint panel does.
YAML files are where credentials, internal hostnames and infrastructure layouts live. Pasting one into a tool that posts it to a backend is a genuine risk, and often against policy. Here the parser is the page itself.
The workspace uses the full width of your screen, the editor is the engine behind VS Code, and it loads after the page is interactive. No interstitials, no signup wall, no ad wedged between the toolbar and your document.
The tools that rank for this term do the basics competently. These are the specific things they leave on the table.
YAML Checker and most of the smaller formatters are built on js-yaml, which has no concept of a comment once parsing is done. Online YAML Tools' prettifier is the same. Format a documented config with any of them and you get your data back without the explanations. That is usually discovered after pasting over the original.
The largest formatter sites offer a save feature that stores your YAML at a public URL with no authentication — an easy click to make by accident with a file full of environment variables. There is no such button here; download writes to your own disk.
Online YAML Tools offers a single spacing control. Sequence indentation, key sorting, flow expansion, quote style and line width are the settings people actually reach for when preparing a config for review, and they are all here.
Every competitor stops at 'is it valid YAML'. None of them tell you that the value you just wrote is valid and wrong. The Norway problem alone has caused enough production incidents to be worth a checkbox.
Several tools mangle or reject a file containing --- separators, which describes almost every real Kubernetes manifest. Each document here is parsed and formatted on its own.
Deployments, services and ConfigMaps are multi-document YAML where indentation is the whole syntax. Format before applying, and catch the duplicate key that would have silently dropped half your env block.
Compose files grow by accretion until indentation drifts. Reformatting gives a consistent shape and confirms the file still parses before you spend a minute waiting for a failed up.
GitHub Actions, GitLab CI and CircleCI configs fail slowly — you push, wait, and get a syntax error. Validating locally first turns a five-minute round trip into a five-second one.
Playbooks and chart values rely heavily on anchors and aliases to avoid repetition. A formatter that discards them is worse than useless here; this one keeps them intact.
APIs speak JSON, configuration speaks YAML. Convert in either direction to feed a config into a script, or to turn an API response into something a human will maintain.
Consistent indentation and optional key sorting mean a pull request shows what actually changed instead of a wall of reformatting noise.
The first two break the parse. The rest parse perfectly and hand your program the wrong value — which is why they reach production.
YAML forbids tabs in indentation; only spaces count. A file can look perfectly aligned and still refuse to parse because one line was indented with a tab. Set your editor to insert spaces for .yaml files.
Every key at the same level needs the same indentation, and nested blocks must be indented further than their parent. Unlike most languages, in YAML the whitespace is the structure — there are no braces to fall back on.
Under YAML 1.1 — still used by PyYAML and many CI systems — unquoted no becomes the boolean false, so the country code NO turns into false. YAML 1.2 treats it as a string. Quote the value as "no" and it means the same thing everywhere.
Defining the same key twice in one mapping is not an error in most parsers. The last value silently wins and the first disappears, so half your configuration never takes effect. The lint panel points at every occurrence.
Unquoted 1.10 is a number, and the trailing zero is gone — you now have version 1.1, a different release. Unquoted 0755 loses its leading zero, and under YAML 1.1 it is read as octal instead. Quote anything where the exact digits matter.
An account number or snowflake ID beyond 16 digits exceeds what a 64-bit float can hold exactly, so the value silently changes. Quote it to keep it a string.
Everything worth knowing about formatting YAML in your browser.
Yes, and that is the main reason to use it. Header comments, inline comments after a value, anchors, aliases and merge keys are all preserved, because formatting operates on the document tree rather than on a plain object parsed out of it. Most online formatters use js-yaml, which discards comments during parsing and cannot put them back.
No. Parsing, formatting, linting and conversion all run as JavaScript in your browser tab, and there is no backend to receive your file. You can confirm it in DevTools: the page loads its own assets and, like most free tools, analytics and ad scripts — but formatting or converting triggers no request, and nothing you paste appears in any request body.
That is the Norway problem. YAML 1.1 treats unquoted y, yes, on, n, no and off as booleans, so a field holding the country code NO evaluates to false. YAML 1.2 treats them as strings. Since parsers in the wild disagree, quote the value. The lint panel flags every occurrence and shows what each version resolves it to.
Both are valid YAML and parse identically. Kubernetes examples usually indent them; many Ansible and Compose codebases keep them flush against the parent key. Pick whichever matches your repository and set the toggle — the point is consistency, not correctness.
Yes. Documents separated by --- are parsed, validated and formatted individually, and the separators are preserved. Converting a multi-document stream to JSON produces an array with one entry per document.
Validation answers 'will a parser accept this file' — unclosed brackets, tabs in indentation, broken structure. Linting answers 'will it mean what you intended' — ambiguous booleans, duplicate keys, numbers that lose digits. A file can pass validation and still fail lint, and those are the failures that reach production.
None imposed by the tool, since nothing is uploaded — the only constraint is your device's memory. Multi-megabyte files format fine on a normal laptop, though very large documents take a moment to render in the editor.
Yes. Once the page has loaded, every feature keeps working with no connection, which also makes it usable where pasting infrastructure config into an external website would breach policy.
Focused syntax checking with real-time error detection when you only need to know whether it parses.
A dedicated converter when moving between the two formats is the whole job.
The same treatment for XML — beautify, validate, tree view and an XPath tester.
Format, validate and explore JSON with a collapsible tree view.
Compare two formatted configs side by side and see exactly what changed.
Every YAML formatter, validator and converter on the site, all running client-side.
No registration, no tracking of your content, no server uploads. Don't just take our word for it:
Your files and text are processed entirely on your device. Nothing is ever sent to us.
Once loaded, this tool keeps working with your Wi-Fi turned off. Try it.
Open your browser's DevTools → Network tab. You'll see zero requests carrying your data.
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