Introducing LightAtom

Open Activity Monitor’s Network tab and you’ll see numbers: bytes in, bytes out, per process. What you won’t see is where those bytes go. Which servers? Which companies? Which countries? Which of the hundred background processes is responsible?

LightAtom is a Mac app built to answer exactly that.

What it shows

• Connections. Every open connection, grouped by the app that made it, with the remote address, port, protocol and how much data it has moved.
• Domain names. The name each app looked up, shown beside the connection that followed. An IP address owned by a CDN tells you little; the domain name usually tells you everything.
• The map. Where your traffic goes, drawn live from a location database on your Mac. With an honest caveat: CDN and anycast addresses don’t really have one location, and the map tells you so.
• Ports. What’s listening on your Mac, which app owns each port, and whether it’s reachable from the network.
• Traceroute. The path to any server, hop by hop, on the same map.

What it doesn’t do

LightAtom doesn’t block anything. That’s deliberate. Firewalls such as LuLu and Little Snitch already do blocking well, and an app that can break your network with one click has to ask you a lot of questions. LightAtom just shows you what’s happening, so you can decide what, if anything, to do about it. It works alongside any firewall.

It also doesn’t read the contents of your traffic. It sees connections, not data.

Privacy

LightAtom runs on your Mac and keeps what it sees on your Mac. There’s no account, and nothing it sees is saved or uploaded.

Free tools, too

Alongside the app, this site has free tools that run in your browser — a DNS speed test, a subnet calculator and more — plus guides to the network commands built into macOS and fixes for common errors. They’re useful whether or not you ever install the app.