The workflow
Open or paste YAML → choose a profile → review syntax and type findings → pick a preset → compare the diff and the semantic status → Apply → download. Apply is one undoable step; Undo restores the exact previous text.
Preview results carry the revision of the source they were made from. If you edit the source, the preview is marked stale and Apply is disabled until it is regenerated.
Status words
Verified equivalent: the output parses to the same graph. Equivalent, keys reordered: same values, different key order (only from Sort keys). Unverified: equality could not be proven; review and confirm to apply. Blocked: the output would change a value, lose a comment or does not parse. Syntax errors: the source does not parse; nothing is formatted.
YAML 1.1 versus 1.2
YAML 1.2 (2009, revised 2021) narrowed which plain words are special. In YAML 1.1, yes/no/on/off/y/n are booleans, 0123 is octal 83, 1_000 is 1000, 12:30 is 750 (base 60) and 2001-12-14 is a timestamp. In YAML 1.2 core, all of those are strings except 0123, which is decimal 123. Many tools still load YAML 1.1, so the Types tab flags these values and can keep them quoted.
Keyboard
Every control is reachable with Tab. In the source editor, Tab moves focus out of the editor rather than inserting a tab, because tabs are not valid YAML indentation. Findings in the Checks tab jump to their line when activated.
Questions
- Which parser does FormatYAML use?
- The open-source yaml package (v2.9.1) by Eemeli Aro, used through its document and token APIs, with FormatYAML’s own lexeme preservation, comment review and graph comparison on top.
- Does it validate Kubernetes or CI files?
- No. FormatYAML checks YAML syntax, structure and value preservation. Platform schemas are out of scope.
- Does it run templates or custom tags?
- Never. Template markers and unknown tags are kept as inert text; no constructor or template engine runs.