Github user pvillard31 commented on the issue: https://github.com/apache/nifi/pull/2587 Hey @JohannesDaniel - just made new tests and can't reproduce what I saw previously... so let's forget about it :) (thanks for the unit tests though!) I tested the EL support for tag validation, working well, thanks for the addition. I'd just make one suggestion: right now for the record tag, "in the case of a mismatch, the respective record will be skipped". I'd suggest to make this behavior configurable through a parameter in the CS: skip the record (current behavior) or throw an exception for the flow file (as you're doing for the root tag validation). Regarding the performance test, it was a GFF => ConvertRecord (XML to JSON) => UpdateAttribute. Don't remember the exact numbers but IIRC it was around 1300 flowfile per second with an XML payload of 6KB (single record in my case). Overall, it's really cool! I'll try to have a look over the code during the week.