HLSLDebugger is available as a website or a standalone desktop program.

This is a debugger for HLSL code. HLSLDebugger can run HLSL either on the CPU using HLSLInterpreter, or on the GPU using WebGPU. It supports typical debugging workflows with breakpoints and stepping, and can debug both fragment and vertex shaders. To start debugging, simply click on a pixel or vertex in the viewport.

The debugger has the ability to import and transpile ShaderToy-flavored GLSL code to HLSL, so that it can be debugged. I've made a Chrome extension that adds a button to the ShaderToy website to do this.