Carball

What Carball Actually Is and How to Use It

Carball is a lightweight command-line utility that sits between your browser and local development servers. It started as a personal project to solve a specific caching problem, and grew into something people actually use in production pipelines. I'm going to walk through what it does, how to install it, and where it breaks. The core problem it solves is that modern dev servers tend to serve stale assets when you're working with multiple entry points or hot-reload cycles. Carball watches your build output and rewrites asset URLs on the fly so your browser always gets the right version without manual cache busting. It's not a build tool. It doesn't replace webpack, Vite, or Turbopack. It's a proxy layer.

How to Install and Run Carball

Installation is straightforward if you have Node.js 18 or later. Run npm install -g carball, then configure a simple JSON file in your project root called carball.config.json. The default config takes three fields: dev server URL, output directory, and optional middleware plugins. Start it with carball --config ./carball.config.json and point your browser at localhost on the port it prints. Here's what the config looks like in practice:

{
  "devServer": "http://localhost:5173",
  "outputDir": "./dist",
  "port": 8080,
  "middleware": []
}

That's it. Your dev server keeps running on 5173. Carball proxies everything from 8080, injects correct asset hashes, and serves your static files from the output directory directly instead of through the dev server. The difference in load times is noticeable on larger projects — we're talking 30 to 60 percent faster page loads during development depending on how many assets you're pulling in. I ran into a specific issue last month that took me about four hours to track down. I was using Carball alongside a GraphQL endpoint that lived on the same dev server. The proxy was intercepting requests to /graphql and returning HTML instead of JSON because Carball defaults to serving index.html for anything it can't match in the output directory. The fix was adding a routes override in the config that explicitly excluded /graphql and any other API paths from proxy handling. Once I added "passthrough": ["/graphql", "/api"] to the config, everything worked cleanly.

Advanced Behavior You Should Know About

Most people configure Carball and forget about it. That's fine until it starts behaving unexpectedly. The asset rewriting logic has a few edge cases that trip people up. The first thing that catches developers off guard is how Carball handles absolute paths in your source code. If you hardcode /assets/images/logo.png in your JS or CSS, Carball will rewrite that to include the correct hash. But if you use template literals with dynamic segments like \`/assets/\${name}.png\`, the proxy can't detect those at parse time. The browser will request the unhashed URL, Carball won't rewrite it, and you'll get a 404. The workaround is to switch to relative paths or use Carball's inject hook to run a custom regex replacement before serving responses. I wrote a small plugin that scans for common dynamic patterns and that cut my debugging time significantly. Another thing that matters is cache invalidation strategy. Carball uses content-hash-based filenames by default, which is correct for production but creates a subtle problem during development. If you change a file and rebuild, the old hashed files stay in the output directory until your build process cleans them. Carball will serve the new hash correctly, but any orphaned files from previous builds just sit there. On a project with heavy asset generation, that directory can grow to several hundred megabytes over a week. The practical fix is to either run a cleanup step before each build or configure Carball's "cleanupInterval" option, which automatically removes files older than a specified number of hours from the output directory.

There's also a limitation around server-side rendering. If your framework does SSR and Carball is sitting in front of it, the SSR response comes back with relative asset paths. Carball rewrites those on the client side after hydration, which means the initial HTML sent to the browser has incorrect URLs. This causes a brief flash of broken assets before the client-side JavaScript fixes them. The solution isn't in Carball itself — it's in configuring your SSR setup to inject the base URL before the response is sent. Most frameworks have a way to do this, but Carball doesn't handle it for you.

When Carball Is the Wrong Tool

Carball works well for single-page applications and static-heavy projects. It does not work well for server-rendered apps that depend on precise URL routing, real-time WebSocket communication through the proxy, or projects that serve large binary files through the dev server. In those cases, you're better off configuring your build tool's dev server directly with cache-busting enabled, or using a proper reverse proxy like nginx in front of your application. I've seen people try to run Carball in front of microservice architectures where each service lives on a different port. It technically works for the static asset part, but the proxy overhead becomes noticeable under load, and debugging connectivity issues across multiple proxied services is frustrating. A simple host-level configuration or Docker networking handles that better.

Getting Carball in Your Project

You can find the package on npm at carball or check the source on GitHub. The README has more detailed configuration options, middleware examples, and troubleshooting guides. Installation through npm or yarn takes about 30 seconds. Configuration usually takes another 10 minutes if you've never set up a proxy layer before. The project is open source and actively maintained. Issues are responded to within a few days on weekdays. If you run into the passthrough problem I mentioned earlier, searching the issues tab will show you the exact config pattern others have used to solve it. One final note that beginners often miss: Carball adds roughly 5 to 15 milliseconds of latency per request because every response passes through the proxy. For most development workflows that's irrelevant. If you're doing performance-critical testing or load simulation, measure with Carball disabled and use it only for day-to-day development work.