rakyll/hey

Hey is a command-line tool for load testing web applications. Load testing means sending a large number of HTTP requests to a server in a controlled way to see how it performs under pressure, how fast it responds, how many requests it can handle at once, and whether it fails or slows down when traffic spikes. Hey is positioned as a modern replacement for ApacheBench (ab), the classic but aging load testing tool. The tool is a single small binary, you download it and run it directly with no installation required. You point it at a URL and specify how many requests to send and how many to send at the same time (concurrency). After the test finishes, it prints a summary with statistics like response times, throughput, and status code distribution. It also supports running a test for a fixed duration instead of a fixed number of requests, rate limiting, custom HTTP headers and methods, request bodies, basic authentication, HTTP/2, and proxies. The examples in the README show the typical patterns clearly: sending 1,000 requests with 100 workers running in parallel, running a 30-second load test, making POST requests with custom data, or adding authorization headers. Results can also be exported as CSV for further analysis. You would use Hey when deploying a new API or web service and wanting to verify it can handle expected traffic levels, when diagnosing a performance regression, or when comparing two server configurations. It is written in Go and available as pre-built binaries for Linux, macOS, and Windows, and can also be installed on macOS via Homebrew.