What problems does the linter catch?

It catches tab characters used for indentation, duplicate keys in the same mapping, a missing space after a mapping colon, unbalanced flow brackets, trailing whitespace, and ambiguous unquoted values that YAML coerces.

Why is yes flagged as a warning?

Under YAML 1.1, bare words like yes, no, on, and off are coerced to booleans. If you intended the literal string, the value must be quoted. The linter warns so you can decide which you meant.

Why can a leading zero be a problem?

A value such as 0755 or 01.2 can be interpreted as octal or as a malformed number depending on the parser. The linter warns so you quote it when you want the exact literal preserved.

Does it fully parse and load the YAML?

No. It is a focused linter that detects the highest-value real-world mistakes without building a full document tree. For full schema validation, run it through your application's own loader as well.

Is my YAML uploaded anywhere?

No. All scanning runs in your browser with JavaScript, so files containing API keys, passwords, or other secrets never leave your device.

YAML Linter — Gera Tools

YAML is whitespace-sensitive and quietly forgiving, which makes its failure modes especially nasty: a tab where a space belongs, two keys with the same name where only the last survives, or an unquoted yes that silently becomes a boolean. This YAML linter scans for those exact gotchas in your browser and explains each one.

How it works

The linter walks your file line by line, tracking quote state so that a # or colon inside a string is not mistaken for a comment or a mapping separator. For each line it checks several rules:

A tab character in the indentation is an error, because YAML forbids tabs for indentation.
Two keys at the same indent under the same parent are reported as a duplicate-key error; in real YAML only the last would win.
A mapping colon must be followed by a space or end of line, so key:value is flagged.
Flow collections must have balanced [ ] and { } on the line.
Trailing whitespace is reported as a warning.

Ambiguous values

YAML 1.1 coerces bare words like yes, no, on, and off into booleans, and a value such as 0755 can be read as octal. The linter warns on these so you can quote them when you mean the literal string or number. For example, in the sample, version: 01.2 and enabled: yes both raise warnings.

Notes

This is a practical linter, not a complete YAML processor — it targets the mistakes that cause real outages rather than building a full document model. Use it as a fast first pass, then load the file through your own application’s parser to confirm the final structure. Everything runs locally, so configs containing secrets stay private.