Ask HN: What is a (non-existant) service or tool that you want as a developer?

Dynamic image generation / hosting.

I give you a baseline image. You dynamically modify that image and host it for me based upon (ideally encrypted) parameters that I pass you.

Example use case: I send an email that features a thermometer that shows how far from $100 your balance is. It dynamically calls this service to generate a thermometer showing your $96 as meaningfully different from my $22.

Anything PDF or something like that on demand, have it generate the templates and whatnot instead of relying in write it all by hand with the technology that recquires me to do so.