The most common mistakes
- Unquoted template. brightness: {{ … }} breaks YAML on the brace. Always write "{{ … }}" in quotes.
- Unquoted on and off. Home Assistant reads YAML with rules where on, off, yes, no mean true and false. to: on never matches; write to: "on".
- Tabs and indentation. Spaces only, usually two. One space off moves a key into another block; the checker reports it as an unknown key.
- entity_id with capitals or spaces. Correct: binary_sensor.hall_motion. Find the exact id in Settings → Entities.
The 2024 syntax
Since 2024.8 a service call is written action: instead of service:, and since 2024.10 triggers:, conditions:, actions: are plural and trigger: state replaces platform: state. The old form still works, so the checker marks it as a tip, not an error.
Errors from the Home Assistant log: Invalid config, Template variable warning. ESPHome configs: ESPHome generator.