How to limit the number of characters for an input field

for example the subject field on an event should only be 25 characters long.

You should be able to limit this in the salesforce field settings. I believe you can olso opt to override the meta data settings by clicking on the field in the model editor (not in a layout) and then define max chatacters for text fields

Hi Jaime,

Raymond is correct. Here’s how to do it in the metadata settings of a specific field, although I would say that it’s generally best practice to change this on the Salesforce side first.

Sincerely,
Karl