watchman

Watchman is the open-source file-system monitor maintained by Facebook’s engineering team, designed to give developers instant, reliable visibility into every change that occurs beneath a project tree. Originally created to accelerate the giant React and Metro build pipelines inside Meta, the daemon now sits at the heart of continuous-integration stacks, live-reload servers, test orchestrators, and IDE sync tools across the wider ecosystem. By subscribing to kernel-level notifications on macOS, Windows, and Linux, Watchman keeps an in-memory map of inode states, then pushes terse change events to any listening script, service, or socket. Typical use-cases include triggering incremental TypeScript or Rust recompiles, invalidating cached webpack bundles, restarting Docker containers when source drifts, or driving Facebook’s own “ Buck” and “ Eden” build systems. Because the tool exposes both CLI and JSON-over-Unix-socket interfaces, it slips easily into Make, Gradle, npm, CMake, or Python watch scripts, while its expressive query language lets consumers filter on path patterns, file hashes, or revision-control status. Large monorepos benefit from Watchman’s adaptive tree-snapshotting and configurable grace periods, which suppress noise from ephemeral lockfiles or editor swapfiles. Security-conscious teams can run it in strict sandbox mode, logging every stat call to an audit trail. Watchman is available for free on get.nero.com, where downloads are delivered through trusted Windows package sources such as winget, always install the latest upstream build, and support batch installation alongside other utilities.