I've been building promptslice.com as a way to create, test, and optimize prompts + tools + context. I needed it when building agents for other use cases so I built it. Unlike Langsmith and some of the other prompt editors, this has a first class editor for your prompt with "Cursor style" chat where you can ask it to make tweaks, overhaul sections, optimize ambiguity, etc.

The demo on the homepage is neat. I see the advantage of the editor.