Does it merge and deduplicate patterns when I pick multiple templates?
Yes — each selected template becomes its own labeled section, and a line already emitted by an earlier template is dropped if a later template repeats it, so the file doesn't accumulate duplicate entries.
I already committed a file I want to ignore now — why is it still tracked?
.gitignore only affects untracked files. To stop tracking something already committed, run git rm --cached <file> (or -r for a directory), then commit that removal.
Should OS/IDE patterns go in this project's .gitignore, or somewhere else?
Common convention: keep language/framework patterns in the project's .gitignore (shared with your team), and put personal OS/IDE noise (.DS_Store, .idea/) in your global gitignore instead (git config --global core.excludesfile).
Which templates are supported?
30 templates covering languages (Node, Python, Java, Go, Rust, Ruby, Swift, C#, C++, PHP, Elixir), frameworks (React, Next.js, Vue, Angular, Django, Flutter, Android, Unity), build tools (Gradle, Maven, Docker, Terraform), and editor/OS noise (macOS, Windows, Linux, VS Code, JetBrains, Vim, dotenv) — a curated subset of the github/gitignore collection.