Guides
Fixes for running local dev servers
The problems that come with running a project on your own machine, each answered first with the command that fixes it today, then with how localhost keeps it fixed.
Port 3000 is already in use
Find what holds the port with lsof, ss or netstat, stop it, and why the error keeps coming back.
Kill leftover dev servers
List every process listening on a port, stop the whole tree, not just the parent, and keep it that way.
Claude Code started a second dev server
Stop the duplicate, then connect Claude Code to localhost mcp so it starts the Services you already run.
Run frontend and backend together
concurrently, a Procfile runner or tmux in one command, and when a window with Dependencies fits better.
How do I run this project again?
Where a project’s commands hide (package.json, Compose, Procfile, Cargo), and how to never look again.
Looking for how a feature works? Read the docs, or seehow localhost compares to pm2, tmux, Docker Compose and others.