Hostflip – a macOS /etc/hosts switcher that detects external edits

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Hostflip – a macOS /etc/hosts switcher that detects external edits

Hi HN — I built hostflip, a native macOS menu bar app for switching /etc/hosts profiles. It is free and open source under the MIT license. The problem I wanted to solve was not just editing hosts entries. It was sharing /etc/hosts with Docker Desktop, VPN clients, scripts, and manual edits without one writer silently erasing another's changes. On first run, hostflip captures a read-only baseline (called Base Hosts) from the existing file and keeps the untouched original as hosts.orig. Active profiles are appended after the baseline in a clearly marked block. Writes are still atomic whole-file replacements under the hood. Before each write, the daemon hashes the live file and compares it with the expected hash. If they differ, it refuses the write; the app shows a diff and asks the user to reconcile the change first. A few other details: - Profiles can live in groups. At most one profile per group is active, while active profiles from different groups and standalone profiles stack together. - After a one-time approval in System Settings, subsequent switches no longer prompt for a password. The root helper is registered through SMAppService and exposes a single XPC operation: atomically replace the hosts file with merged content. The app and daemon verify each other's signing identity. - The bundled CLI shares the same workspace as the app and supports structured JSON output. hostflip doctor dev.example.com traces a hostname from profiles through the merged output and the live /etc/hosts file to the system resolver. - Remote profiles can refresh from HTTPS sources on a schedule. There is also an importer for existing SwitchHosts configurations. - The editor has cross-profile hostname/IP search, comment toggling, basic validation for malformed hosts lines, and stays responsive with large remote profiles. The app is built with Swift and SwiftUI, distributed through Homebrew or a signed and notarized DMG, and currently requires macOS 14 or later on Apple silicon. Intel, Windows, and Linux are not supported. I would especially like feedback on the conservative drift behavior: if another process changes /etc/hosts, hostflip blocks further writes to the system file until the user reviews the diff. How do you handle multiple writers to the hosts file, and would you expect a different reconciliation model?