Guides

Fixes for the problems that stop a project on your Mac, step by step, with the Terminal commands first.

How to run Claude Code in parallel with git worktrees

One repository, several Claude Code sessions, no collisions. Each gets its own worktree, branch, port and database, and you keep the task list in one place.

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How to give each git branch its own database copy

Branches keep your code apart, but not your data. A copy of the development database per branch stops one branch's migration from breaking another.

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Error: listen EADDRINUSE: address already in use (how to fix it on Mac)

Node is telling you another program already holds the port. Here is how to find that program, stop it safely, and keep it from coming back.

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How to find and stop the process using a port on Mac

One Terminal command shows what is listening on any port. Then check what it is, and stop it the right way, because a database needs different care than a dev server.

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How to use a custom local domain instead of localhost:3000 on Mac

Port numbers are hard to remember and easy to mix up. A name per project, like shop.localhost, fixes both. Here is which endings to use and how to set one up.

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How to switch Node version per project on Mac

Pin each project to its Node.js version with .nvmrc, switch automatically with nvm or fnm, and make the wrong version fail loudly instead of strangely.

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Port 3000 already in use on Mac: how to find it and free it

The error means another program already holds the port. Find it with one Terminal command, check who started it, stop it safely and keep it from coming back.

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How to keep project notes and todos out of Git

Every project collects notes, links and half-ideas. Here is where to keep them so they stay next to the project, never land in a commit, and your AI tools can read them.

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Run multiple Claude Code, Cursor and Codex agents on one project

Give each agent its own Git worktree, port, database copy and .env, so Claude Code, Cursor and Codex can work on one project without breaking each other.

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Why won't my project start? A checklist for local development on Mac

Five checks cover almost every "it worked yesterday" on a Mac. Go through them in this order and you will usually find the cause in a few minutes.

Also see the comparisons and the documentation.