Visual Shader Studio is a complete HLSL shader creator for Windows which allows importing and exporting direclty to Game Maker Studio.

Features:

Live HLSL shader editing.
2D and 3D previewing.
Import and Export as full GM:S HLSL supported shader files.
Color formatted text.
Familiar interface similar to Game Maker Studio Shader editor.
Drag and drop texture for sampler stages.
Code snippets to get you started and help with learning HLSL.
Example shaders provided.