When your Mac isn't right

Slow, hot, out of memory, out of space or draining its battery: what's causing it, and how to fix it with the tools already on your Mac.

• Why is my Mac so slow?A Mac slows down for five reasons: memory, one busy app, heat, a full disk or background work. How to tell which one it is in a minute, and fix it.
• Port 3000 is already in use on my Mac. How do I free it?EADDRINUSE on a Mac? Find what's holding port 3000 (or 5000, 8080) with one command, stop it safely, and why port 5000 is often AirPlay Receiver.
• Claude Code is using too much memory on my Mac. What do I do?Every open Claude Code session holds memory, and so do the MCP servers and dev servers it started. How to find forgotten sessions on a Mac and close them.
• Why is my Mac's fan so loud, and why is it running hot?A hot Mac or a loud fan means something is working the chip hard. How to find the app responsible, what's normal, and how to cool your Mac down.
• What does memory pressure mean on a Mac?Memory pressure, not Memory Used, says whether your Mac is short of memory. What green, yellow and red mean, what swap and compression are, and what to do.
• My Mac's storage is full. What's taking up the space?What's in System Data, where developer caches hide (Xcode, Docker, node_modules, AI models), and what's safe to delete when your Mac's storage is full.
• Why is my MacBook's battery draining so fast?Which app is draining your MacBook's battery? How to find it with Activity Monitor's Energy tab, the usual causes, and how to check battery health.
• Why is my Mac slow after a macOS update?After a macOS update your Mac re-indexes, re-analyses photos and re-syncs iCloud, which can take a day. What's normal, what isn't, and how to speed it up.