Bandwidther

SwiftUI menu bar app for monitoring application bandwidth use.

Note

This app was vibe coded using Claude Opus 4.6 and GPT-5.4. I do not have deep knowledge of macOS networking or SwiftUI such that I can confidently evaluate the end result.

Features

• Live per-process download/upload rates via nettop
• Internet vs LAN connection classification
• Reverse DNS resolution for remote destinations
• Sparkline bandwidth graph (last 60 seconds)
• Two-column popover panel from the menu bar

How measurement works

Bandwidther uses macOS command-line networking tools rather than packet capture or private APIs.

• Per-process bandwidth comes from nettop in per-process summary mode. The app runs nettop in delta mode, takes a baseline sample plus a 1-second follow-up sample, and uses that second sample as the current download/upload rate for each process.
• The cumulative byte totals shown in the UI come from the baseline nettop sample. Those are process-level totals reported by nettop, not totals maintained independently by the app.
• Connection summaries come from lsof -iTCP -n -P. The app parses active TCP sockets, attributes them to processes using lsof output, and classifies remote endpoints as internet or LAN/local using address heuristics.
• Reverse DNS is done separately in the app using getnameinfo, so destination names are best-effort and may be missing even when the raw IP address is shown.

Important limitations:

• The connection view is a snapshot of currently visible TCP sockets. It is not a packet-level audit and it does not currently include UDP traffic in the summary panels.
• LAN vs internet classification is heuristic. Private IPv4 ranges, loopback, link-local IPv6, and unique-local IPv6 are treated as local.
• If nettop or lsof is unavailable or denied by the system, the app may be unable to collect some measurements. Recent versions of the app surface nettop failures in the UI instead of silently showing zero traffic.

Building

git clone https://github.com/simonw/bandwidther
cd bandwidther
swiftc -parse-as-library -framework SwiftUI -framework AppKit -o Bandwidther BandwidtherApp.swift
./Bandwidther

Requires macOS and Xcode command line tools (xcode-select --install).