Checker · runs in your browser
Find the line that broke your config
Home Assistant tells you the config is invalid and not much else. Paste it here and get the line number, what is wrong with it, and how to fix it.
The mistakes this catches
Tabs
The number one killer. YAML forbids tab characters for indentation, and most editors insert them without telling you. One tab stops the entire file loading.
Templates that aren't quoted
A value starting with {{ has to be in quotes. Without them YAML thinks you are opening a map and gives up halfway through the line.
on: as a key
YAML reads on, off, yes and no as true and false. So on: quietly becomes true: and everything underneath it never runs — with no error anywhere.
Keys defined twice
The second one wins and the first disappears without a word. Easy to do after copying a block from a forum.
Invisible characters
Copying from a web page often brings non-breaking spaces along. They look exactly like a space and YAML rejects them.