Best practices for custom tags that interop with Lightroom

[winterminute]

I'm working on a custom app that will produce metadata for a photo.  I could store this in a completely separate database and then build an app to read that database, but Lightroom-based workflow might be the easiest.  I know that photo metadata is the wild-west.  What is the best way to write custom metadata back to the file such that I can search/filter on it in Lightroom?  I know I'll have to explicitly read the metadata in LR, but it's not clear how custom tags work.  I'd prefer not to overload Keywords.

[StarGeek]

What is the best way to write custom metadata back to the file such that I can search/filter on it in Lightroom?

I doubt that custom metadata can be searched/filtered in LR.  Though to be fair, my LR is very old so I can't test it. LR is probably only going to read what data it has been programmed to, i.e. data that follows the standard metadata specs.

You can test it out by downloading the example.config file and then writing to example XMP tag there.  Save the config file in the same directory as exiftool and then use this command
exiftool -config example.config -NewXMPxmpTag=Test testfile.jpg

Then load the test file into LR and see if you can find the NewXMPxmpTag tag.

As an alternative, Photool's IMatch uses exiftool on the back end and because of that, any metadata read by exiftool can be added and searched upon.  For example, in this post, IMatch can now read GUANO (Grand Unified Acoustic Notation Ontology i.e. bat sound recordings) data.  The linked post shows what ended up displayed in Imatch. It is pricey, but it is not a subscription service, and there is a bit of a learning curve.