$ yamlcheck
Syntax check with the error line. Data never leaves the browser.
input
Typical YAML errors
Tabs instead of spaces. YAML forbids tabs in indentation. «found character that cannot start any token» is almost always a tab.
Mixed indentation. Sibling keys with different space counts. In Helm charts — usually a wrong nindent value.
Unquoted special characters. Values with :, #, {, leading * or & need quotes.
The Norway problem. In YAML 1.1 no, yes, on, off parse as booleans, and 3.10 as the number 3.1. Country code NO becomes false. Quotes fix it.
Multiline values. | keeps line breaks, > folds them — a common ConfigMap bug source.