Is it possible to use the /app/recordscatalog/rcendpoint.nl endpoint on server side restlet or only within a client side suitelet? This is Tim's suitelet query tool I'm referencing. The XMLHttpRequest seems to only work client side.

no, clientside only

That’s unfortunate, thanks @battk. I was attempting to automate export of schema. I’ve tried using the suitetalk meta data apis, but they include fields you can’t actual query within suiteql. I guess I’ll just make a suitelet that I manually run whenever my schema needs a refresh.