I really like it. I particularly like that you've resisted the temptation to include SQL itself or the jq queries in the DSL.

The validation piece makes it feel a bit a bit like the Rails mindset for people who work better in FP.

I'd make a could of suggestions for the docs: Maybe a bit more discussion of how we'd test our webpipe code. I see why you've called them 'middlewares' but, maybe the term 'macros' or 'pipeline functions' might avoid confusion with express/connect middlewares

Ooh, I like “pipeline functions”!

And thanks for the motivation to for figuring out a good way to talk about testing and generally clean up the (very messy) docs.

It’s comments like yours that give someone the drive to continue.