@protean Pymakr is indeed using the zlib.decompress() micropython function for this feature. Normal upload also still works of course, but this way is faster for large files. Let me give you some pointers on how to code it: The zlib function on the micropython side is documented here. Pymakr is compressing the files before uploading (here using this python file), writing the compressed file to the board with os.write() like always, and then decompressing them right after that (here). It'll definitely make uploading bigger files faster. Just realise that for files under 4k, it's actually slower because the overhead of compressing/decompressing is bigger than the savings of compressing the file.