YAML Formatter & Validator

YAML ("YAML Ain't Markup Language") is a human-readable data format used for configuration files across almost every modern developer tool — Docker Compose, Kubernetes manifests, GitHub Actions workflows, Ansible playbooks, and countless application config files all use it. Its appeal is that it reads almost like plain English: indentation defines structure instead of the braces and brackets JSON needs, so a YAML file tends to be shorter and easier to skim than the equivalent JSON. That same reliance on whitespace is also YAML's biggest source of bugs. Because indentation is meaningful, a single misplaced space can silently change what a key belongs to, or break parsing outright. Tabs are not permitted for indentation in standard YAML (only spaces), and mixing tab and space indentation is one of the most common causes of "why won't my CI pipeline parse this file" bug reports. This formatter re-indents a document to a clean, consistent 2-space standard, which both fixes cosmetic inconsistency (mixed 2-space and 4-space blocks in a file edited by different people) and, as a side effect of round-tripping through a parser, surfaces structural mistakes that were previously hidden by inconsistent whitespace. This tool implements a lightweight, hand-rolled YAML parser and serializer covering the constructs people actually hit day to day: nested mappings (key: value blocks), sequences (- item lists, both block style and inline flow style like [a, b, c]), scalar values (strings, numbers, booleans, null), inline flow mappings ({a: 1, b: 2}), and quoted strings (both single and double quotes, including escaped characters in double-quoted strings). It deliberately does not implement the full YAML 1.2 specification — in particular it does not support anchors and aliases (&anchor / *alias), custom tags (!!type), multi-document streams (--- separators for multiple documents in one file), folded/literal block scalars with all their chomping-indicator edge cases (| and > with +/- modifiers), or merge keys (<<:). If a document uses any of these, format/validate may report an error or produce an approximation rather than a byte-perfect equivalent — for those advanced features, a dedicated YAML library (like js-yaml) is the right tool, and this widget will say so clearly if it hits a construct it does not recognise. There is no "minify" concept for YAML in the way there is for JSON or CSS, because YAML's structure depends on line breaks and indentation — removing them would either produce invalid YAML or force a switch to YAML's alternative "flow" syntax (the JSON-like {}/[] form), which is really a different serialization rather than a compressed version of the same one. Rather than bolt on a confusing pseudo-minify button, this tool offers exactly two actions: Format (pretty, block-style, 2-space indent) and Validate (parse and report errors) — both fully useful, neither pretending to be something it is not. The validator reports the first parsing problem it encounters together with the line number where it occurred, which is normally enough context to find and fix the issue (an unclosed quote, an unexpected indent level, a list item at the wrong depth). Because everything happens client-side, you can safely paste real configuration files — including ones with secrets in them for a quick formatting check — without that content ever leaving your browser tab.