loadcell

LoadCell is a free desktop application for load testing HTTP endpoints. Load testing means sending many requests to a web address at once to see how it holds up under traffic, and most dedicated tools for this cost money on a subscription basis. LoadCell runs locally on your machine and produces the same kind of results without the monthly fee.

The app lets you choose how to shape the incoming traffic: a constant number of concurrent requests, a ramp that starts low and increases over time, or a hand-drawn curve where you sketch out a custom pattern with adjustable segments (linear, exponential, or stepped) and an optional noise layer. While a test runs, the app shows live metrics updated every 100 milliseconds, including response time percentiles (p50, p95, p99), requests per second, and breakdowns by HTTP status code so you can see how many responses are errors vs. rate limits vs. successes.

Beyond running tests, the app includes a Postman-style sidebar for saving HTTP requests, so you can define a target endpoint once, including headers and request body, and reuse it across tests. Every completed test run is saved to disk with its configuration and metric history, so you can pull up old runs and compare results over time.

LoadCell is built with Wails (a framework for building desktop apps in Go), a Svelte frontend, and D3 for the charts. Prebuilt downloads are available for macOS (Apple Silicon and Intel), Windows, and Linux. Building from source requires Go, Node, and the Wails command-line tool. The repository also includes a small Express-based test server with nine routes that return different response patterns, useful for trying out the app without pointing it at a real service.

The project is licensed under GPL-3.0 and is maintained by one developer as a side project.