Each item has a relevant description & examples.

🐬
When an error is found, the required field is highlighted and the cursor is placed there.
High
🐬
Tips without user criticism.
Middle
🐬
When the button is not active there is a hint why.
Middle
🐬
The text of the error states the possible cause and the following actions (if the user cannot correct the error) for example: "We are updating the server. Try in 2 hours"
Middle
🐬
Error pages 404 and 503 tell the user what to do next.
Middle
🐬
The use of an exclamation mark (!) in errors is avoided.
Low
🐬
All errors are written in the same style and Tone of Voice.
Low