@misha Thanks a lot for your feedback! As a next step I planned to improve the error reporting for the client, so that in case the validation fails, the client receives some message indicating which part of the FIX message is invalid. I could make use of spec's granular error reporting there I think. I will also have a look at custom generators and think about how I could apply them to the internal edn representation of the parsed FIX messages. A nice encoder to produce FIX messages also sounds like a good idea! 👍