GameMaker' Visualizer is a web-based program with two primary functions:
1. DnD/GML highlighting: The program can take a piece of code or a snippet of "object information", highlight expressions and DnD block icons in it, and output HTML code (for sites/blogs) or BB code (for forums).
2. DnD->GML conversion: Given an aforementioned snippet of "object information" with DnD blocks, the program can convert it into equivalent GML code. The conversion process should be rather precise and any quirks (e.g. conditions/actions applying to an object type) are handled automatically.
A small introduction to functionality and reasoning:
A GIF of the thing in action:
The program is open-source and the code is available on Github.
Should be convenient.