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Whistle

Free#7 of 27 in Web Debugging Proxies

Whistle: A flexible open-source proxy for inspecting, replaying, and mocking network traffic. Ranked #7 of 27 in Web Debugging Proxies by our editors (8.6/10); pricing: Open source; best for open-source teams needing flexible proxy modes.

8.6/10Editor score

Visit Whistle

Whistle8.6 Visit Whistle

At a glance

Editor score
8.6 / 10
Pricing
Open source
Best for
Open-source teams needing flexible proxy modes
Paid from
Free
Facts checked
20 Sep 2026

Where it wins
- Captures and modifies HTTP, HTTPS, HTTP/2, WebSocket, and TCP traffic
- Supports proxy modes, replay, custom requests, and response mocking
- Runs across macOS, Windows, Linux, and headless environments
Where it doesn't
- Dedicated breakpoint rules are not established as a feature
- Its workflow centers on proxy traffic rather than general app observability
- Protocol and interface expansion relies on plugins

Our verdict on Whistle

Whistle is an open-source network debugging proxy for developers and technical teams working across desktop, browser, and command-line environments. It captures and modifies HTTP, HTTPS, HTTP/2, WebSocket, and TCP traffic, while also supporting HTTP, HTTPS, SOCKS, and reverse proxy modes. Its feature set covers request and response editing, replay, redirection, response mocking, WebSocket and TCP frame control, and remote DOM inspection through Weinre and Log.

Whistle uses an open-source model and is distributed under the MIT license. A desktop client is available for macOS, Windows, and Linux, while the command-line version supports headless Linux servers and other environments. This makes it a practical fit for teams that need the same proxy-oriented debugging approach across local development and server-side workflows. Plugins can extend protocol and interface capabilities, giving teams a way to adapt the tool beyond its built-in behavior.

Its strongest area is the depth of traffic handling: rules can modify requests and responses, the Network interface supports replay and editing, Composer constructs custom HTTP requests, and local files or inline content can provide mocked API responses. WebSocket and TCP frames can also be inspected and controlled. Teams choosing Whistle should value flexible proxy modes and open-source extensibility. Teams that specifically need a verified breakpoint-rule workflow or broader application observability should choose a tool focused on those capabilities instead.

Your product? Our editors can test Whistle in depth and publish a review, labelled as paid · from $149/mo →

Whistle pricing

Plans Open sourceFree Free to use — no paid tier required for the core job.

See plans on wproxy.org

Whistle fact sheet

Free plan	Not verified
Paid from	Free
Platforms	Not verified
Request/response editing	Yes
Breakpoint rules	Not verified
Traffic replay	Yes
Response mocking	Yes
WebSocket inspection	Yes
Proxy chaining	Yes
Deployment	Desktop, Self-hosted
Platforms	Web, Windows, macOS, Linux
Support	Docs, Community
Built for	Solo, Small business, Mid-market (editorial estimate)
Pricing	Open source
Website	wproxy.org
Facts checked	20 Sep 2026

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The editor score above is our own research. What this page doesn't have yet is a reader's view — what you used Whistle for, what worked and what didn't. No stars are seeded and no review is paid for; an editor reads every one before it appears.

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Featured on iTechGuides

Whistle is listed in our Web Debugging Proxies directory. Add the badge to your site — it links back to this page.

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Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026

Advertiser disclosure: iTechGuides is reader-supported. Vendors can pay for top positions in our rankings and for a place on other products' pages, and we may earn a commission when you click some links. Bought places stand at the number bought; this page and our disclosure say so. Paying vendors may get a fuller, more detailed review from our editors, and that review can change their score. How we rank.

Last updated 7 Oct 2026 · How we research and update