Disclaimer: This guide assumes that you are already familiar with OMORI mod development, and that you know where some files need to go. You should also already know how to fix your OMORI installation, in case you break it.
Furthermore, some mods might not work in SDK mode.¹⁾

To get dev tools in OMORI, which can be very helpful in debugging your mod, you need to do a few steps:

1. Download the SDK edition of the exact same NW.js version that OMORI is using (for OMORI v1.0.8, that's nwjs-sdk-v0.29.0-win-x64.zip).
2. Drag all your files into the OMORI folder and choose replace / overwrite
3. Add this code to www/js/main.js to disable SDK mode protection:

   window.navigator.plugins.namedItem = function() {
       return null;
   }

4. Rename OMORI.exe to something else, like OMORI_old.exe, and rename the new file nw.exe to OMORI.exe
5. Launch the game and press F12 to open the dev tools.