Is there a good tool that checks the schema to determine custom fields and their use in triggers, page layouts, classes, etc? We have a couple objects that are getting close to the 500 max and it would be nice if there were a better way than having someone get a list of custom fields for an object manually and then searching every page layout, class, and trigger for use of each field.
Not exactly what you want but you can use FieldTrip, this App(free) checks all the records that match a given query and allows you to report on their usage. So you can tell which fields are being used and which ones are not really in use.
I'm not aware of any tools that automate this, but here are some ideas:
Pretty old thread but adding another option. I have a free and open source app that scans the fields in your Org and returns the components it's used in (Workflows, Processes, Page Layouts, Apex etc).
Keep in mind that returning fields in Apex and VF is not 100% accurate, as a field with the same API name on different objects would return as being found in a class, even though it might not (as others have mentioned).
Also, it can take quite a while to run on large Orgs.
Source Code: https://github.com/benedwards44/schemalister
I have a local java tool that does that but accuracy is ~95% and does not cover reports, email templates, LEX comps at this point.