Finch

A tiny, fast macOS browser router. Set it as your default browser; it routes each URL to the right browser based on rules in ~/.finch.js.

• ~700 LOC Swift + a 1.5KB embedded JS URL polyfill
• ~5µs hot-path latency on the common case (well under perceptible)
• Native JavaScriptCore, no bundler, no transpiler, no Electron
• Config is real JavaScript — simple cases look like data, full power available

Why

Existing macOS browser pickers either lack power (Browserosaurus, Bumpr) or carry significant complexity (Finicky ships ~2,900 LOC plus a Babel/esbuild/goja config pipeline). Finch keeps the powerful parts of Finicky's design (graduated match types, opener context, URL rewriting) but compiles config helpers to native Swift code so the hot path stays in Swift, not JS.

How Finch compares

	Finch	Finicky	Velja	Choosy	Browserosaurus
Source LOC	~700	~2,900	closed	closed	~4,200
Hot-path latency	~5 µs	unknown	—	—	—
Memory footprint	~17 MB	~30 MB	—	—	~150 MB
Programmable rules	✅	✅	🚧 URL only	❌	❌
Modern ES2020+ in config	✅	❌ (ES5.1)	—	—	—
Caller app routing	✅	✅	✅	✅	❌
URL rewriting	✅	✅	✅	❌	❌
Tracking-strip helper	✅	🚧 manual	✅	❌	❌
Bundler / transpiler	none	Babel + esbuild + goja	—	—	Vite + Forge
Open source	✅ MIT	✅ MIT	❌	❌	✅ (archived)
Free	✅	✅	$8	$10	✅
Actively maintained	✅	✅	✅	✅	❌ (Aug 2025)

Full feature matrix across all 18 alternatives we evaluated: COMPARISON.md. Finch's own implementation status and roadmap: FEATURES.md.

Install

Requires macOS 13+ and Xcode Command Line Tools (xcode-select --install).

Via Homebrew (recommended):

brew install --cask expelledboy/finch/finch

The cask builds from source on your machine — no Developer ID needed, no Gatekeeper warnings. See docs/homebrew.md for how the distribution works and the release process.

From source:

git clone https://github.com/expelledboy/finch
cd finch
make run

Then launch Finch (🐦 in your menu bar), open System Settings → Desktop & Dock → Default web browser and select Finch. Edit ~/.finch.js to define your rules — see examples/finch.example.js.

Finch handles http, https, and mailto URLs only — it deliberately does not register as a viewer for local HTML files. open foo.html is a separate LaunchServices binding (public.html) that routes to whatever app you've chosen via Finder → Get Info → "Open with… → Change All", or programmatically with duti:

brew install duti
duti -s app.zen-browser.zen public.html  all   # replace with your bundle id
duti -s app.zen-browser.zen public.xhtml all

Configuration

Drop a JavaScript file at ~/.finch.js. See examples/finch.example.js.

module.exports = {
  default: "zen",

  browsers: {
    zen:    "app.zen-browser.zen",
    prisma: "com.talon-sec.Work",
    chrome: { id: "com.google.Chrome", args: ["--profile-directory=Work"] },
  },

  // All matching rewrites apply, in order
  rewrite: [
    strip("utm_*", "fbclid", "gclid"),
  ],

  // First matching rule wins
  rules: [
    { match: domain("paymentology.atlassian.net", "datadoghq.com", "zoom.us"),
      open: "prisma" },

    { match: /github\.com\/(paymentology|tutuka)\//, open: "prisma" },

    // Full power: any predicate function works
    { match: (url, ctx) => ctx.modifiers.option, open: "zen" },
  ],
};

Match types

Syntax	Matches	Notes
"example.com"	hostname, exactly or as subdomain	Most common — bare strings are hostname patterns, not full URLs
domain("a.com", "b.com")	any of these hostnames	Compiled to a single fast check
from("com.tinyspeck.slackmacgap")	URL was opened by this app	Caller bundle ID
running("us.zoom.xos")	this app is currently running
/regex/	regex against full URL	For path-specific rules
(url, ctx) => bool	anything	Slow path (~5µs extra), full power

The ctx argument has ctx.url, ctx.opener.bundleId, and ctx.modifiers.{shift,option,command,control}.

Browser targets

Syntax	Means
"zen"	Look up zen in browsers dict
"app.zen-browser.zen"	Direct bundle ID
{ id: "com.google.Chrome", args: ["--incognito"] }	Bundle ID with launch args
(url, ctx) => "zen"	Dynamic target
null	Suppress — do nothing

Rewrite rules

Syntax	Effect
strip("utm_*", "fbclid")	Remove these query params (supports * suffix)
{ match: ..., url: "..." }	Replace URL when match hits
{ match: ..., url: (u, ctx) => ... }	Transform URL via JS

A URL constructor is available inside predicates and rewrites for parsing.

Commands

make build                          # build Finch.app
make run                            # build + register + launch
make test URL="https://..."         # dry-run a URL through the rules
make clean

To reload config after editing ~/.finch.js:

kill -HUP $(pgrep -f Finch.app/Contents/MacOS/Finch)

Or use the menu bar icon → Reload Config.

The binary also has --bench N <url> for in-process resolve benchmarking.

Performance

Measured on Apple Silicon, macOS 15, release build, 100k iterations.

Path	Latency
Default fallback (no rule match)	5.2µs
domain() match	5.4µs
Subdomain match	4.9µs
Regex match	4.5µs
Tracking strip + match	8.7µs
User function predicate	~10µs

For comparison: macOS dispatching the Apple Event from the originating app to Finch takes ~1–5ms. Finch's contribution to click-to-browser latency is in the noise.

The trick: domain(), from(), strip() etc. return marker objects like {__type: "domain", hosts: [...]} that Swift recognizes at config load and compiles to native NSRegularExpression / Set<String>. The Swift→JS bridge is only crossed for user-written (url, ctx) => ... predicates.

Architecture

File	LOC	Responsibility
Sources/Finch/main.swift	6	Bootstrap
Sources/Finch/AppDelegate.swift	112	Apple Event handler, hot path entry, NSWorkspace.open
Sources/Finch/Loader.swift	46	Read ~/.finch.js, evaluate via JSC, return module.exports
Sources/Finch/Helpers.swift	101	Embedded JS prelude: URL polyfill + domain/from/strip helpers
Sources/Finch/Engine.swift	442	Marker compilation + native hot-path resolver

License

MIT — see LICENSE.