A GUI for mitmproxy on Mac
mitmproxy is excellent, free, and scriptable to the moon. It's also a terminal program. Its browser view, mitmweb, helps, but if what you actually want is a native Mac window where you click a request and read it — without an addon, a Python script or a keyboard cheatsheet — that's a different tool. elcapture is built to be that window.
What mitmproxy is great for
Automation and scale. It's open source, runs on anything, and its Python addon API lets you rewrite, record and transform traffic in code. For CI, for a server, for a one-off script that mangles ten thousand requests, mitmproxy is hard to beat and costs nothing. If you're comfortable in the terminal and you want programmatic control, stay there.
Where a native GUI wins
Everyday interactive debugging is faster with your eyes and a mouse than with ? for help and arrow keys through a TUI. elcapture gives you the same man-in-the-middle capture — a local certificate, decrypted HTTPS, your own traffic — in an interface where the request list, headers, bodies and timing are just there, formatted, filterable, clickable.
The things you'd script in a mitmproxy addon are buttons here: pause a request on a breakpoint and edit it, map a response to a local file, rewrite a header, replay it in the API client. When a rule isn't enough, there's still a script engine. You trade mitmproxy's cross-platform, free-and-open nature for a native Mac app you buy once ($29 Pro, free during the beta), and for a lot of time you'd otherwise spend in config files.
Use both, honestly — mitmproxy for pipelines, elcapture when you want to look at traffic and move fast.