Official repo: https://github.com/miktaew/yet-another-idle-rpg
Official release: https://miktaew.github.io/yet-another-idle-rpg/
Dev repo: https://github.com/miktaew/yet-another-idle-rpg-dev
Dev release: https://miktaew.github.io/yet-another-idle-rpg-dev/
Be warned, the game balance remains a WIP Using the "export" feature every now and then is highly recommended, even on main release, since there's always a risk of some gamebreaking bugs having made it through the testing undetected
To run the project locally, you will need a server - even some basic static server will be enough, as it's only about CORS policy. Npm module 'live-server' works perfectly for this purpose https://www.npmjs.com/package/live-server
Making actual changes in code will require either running the build script after installing esbuild, or simply changing script source in index.html from dist/bundle.js to src/main.js
For modding purposes, it's recommended to at the very least take a look at the dev repository, as there's always a possibility it already contains things you wanted to add, or has code changes that will make your work easier, or at least has a fix to a bug you found
Please keep in mind that the default branch you will see here is the master branch, while the one that's hosted is the gh-pages branch; on dev, the former might often have code that does yet not correspond to what you will see while playing
Consider also calling Verify_Game_Objects() in the console, which is a custom built-in tool that will go through most of the content, checking things like properties having acceptable values, or references to other objects being correct. While neither infallible nor covering everything, it might save you a lot of time and annoyance.
If you make an actual mod, it will be highly appreciated if you either make it as a fork of either repository, or if you at least let me know about its existence.