JSON to YAML Converter

Two ways of writing the same thing

JSON and YAML hold the same things: text, numbers, true and false, null, and lists and mappings of those. What differs is the punctuation. JSON marks structure with braces, brackets and commas; YAML marks it with indentation and dashes, which is why a Kubernetes manifest reads like a document and an API response reads like a machine wrote it. Converting between them is re-punctuation, not translation — which is precisely why the few things that do not survive the trip are worth naming.

Why this page asks the direction instead of guessing

Since YAML 1.2, every valid JSON document is also a valid YAML document — with one asymmetry worth knowing: a duplicate key such as {"a":1,"a":2} is resolved silently to its last value by JSON.parse, while the same key written twice in YAML is refused outright. That exception aside, then, a converter that detected what you had pasted would see JSON, correctly conclude "this is YAML", and hand it straight back. The direction is a choice here because the alternative is a tool that is wrong in one direction and cannot tell.

The three mistakes that break YAML

Almost every YAML file that will not parse fails for one of three reasons. A tab was used to indent a line, which YAML forbids outright — and which is invisible in most editors. A line is indented to a level that lines up with nothing above it. Or the same key appears twice in one block, which YAML does not allow. This page names which of the three it is and the line it is on; most converters print the parser's own words, which describe the parser's state rather than your mistake.

What the trip to JSON loses

Comments. JSON has nowhere to put them, so they are dropped, and this page says so under the result rather than letting you discover it in a code review. Anchors and aliases are expanded into the values they stand for, because JSON cannot refer to a value twice. And two things YAML can hold have no JSON spelling at all — .inf and .nan — so rather than write them as null, which is what the browser's own JSON.stringify does without a word, this page refuses and tells you which value it was.

Dates stay strings

Under YAML 1.2's core schema, 2001-12-14 is text unless something asks for it to be a date. Older tools built on YAML 1.1 turn it into a timestamp, and turn no into false and 012 into ten — the famous "Norway problem", where the country code NO becomes a boolean. This converter reads by 1.2, so NO and dates stay strings — though 012 becomes the number 12, as 1.2 says it should. And it writes YAML that a 1.1 reader cannot misread either: strings like "NO", "yes" and "2001-12-14" are quoted on the way out, so the file means the same thing to PyYAML as it does here.

If the JSON side is the problem

A document that will not convert because the JSON itself is broken gets the same treatment the JSON Formatter gives it: the line, the column, and what the mistake actually was — a trailing comma, a single quote, a stray Python True.

Nothing is uploaded

Your browser does the work. Nothing is sent anywhere, and the test suite for this page checks every request the converter makes and fails if one of them could carry the text. YAML files are configuration, and configuration is where the credentials live.