Finicky is a macOS application that acts as a user-configurable default browser router. When the OS hands an http/https/finicky URL to Finicky, the Go core captures the originating app (name, bundle ID, path, window title), expands known short URLs via redirect following, and evaluates a user-provided JavaScript or TypeScript configuration inside an embedded goja runtime. The configuration supports wildcard, regex, and function matchers, URL rewrites, per-browser profiles, and custom launch arguments. The resolved target browser is then opened via the macOS `open` command with appropriate profile flags for Chromium and Firefox. The app also includes a WKWebView-based configuration and troubleshooting window built with Svelte, a JSON rules fallback mode for users who don't want to write JS, and a browser extension for alt-click or context-menu opening through Finicky.