Every time I changed an API endpoint, the ritual was the same.
Build the request in Postman. Confirm it works. Then re-describe the
exact same endpoint in a k6 script to see if it held under load. Two tools. Two configs. Two places to forget to update.
The load test always drifted out of sync with what I'd actually built - which is a great way to ship a regression you "tested." And lately there's a second tax: my client wants an account, and my endpoints sync to someone else's cloud.
These were never two problems
Building a request and breaking it are the same workflow. The only reason they live in two tools is that no GUI client could push real load - Electron and Node.js hit a wall long before the network does.
So I built Vayu: a REST/GraphQL client and a native load tester in one desktop app. The request builder feels like Postman. Underneath it is a C++20 engine.
"Native speed" - show me
Fair. Same mock server, same MacBook Pro M3 Pro, matched concurrency,
measured from the CLI:
| Client | req/s @ 128 conns |
|---|---|
| wrk | 56,802 |
| vegeta | 53,811 |
| Vayu | 52,825 |
~93% of wrk and on par with vegeta - from inside the GUI you build requests in, with the dashboard streaming metrics the whole time. The full methodology and a one-command reproduction script are here.
The part I care about most
No account. No cloud. No telemetry. Every byte stays on your machine - so it works behind corporate firewalls and on air-gapped networks where SaaS clients simply can't.
How it works (briefly)
A native C++ engine runs as a local sidecar; the Electron UI talks to it over local HTTP. The UI never blocks on the request load, so it stays responsive even at tens of thousands of req/s.
Try it
Free, open source, runs on macOS, Windows, and Linux (one-command install on Mac). If the two-tool tax has ever bitten you, I'd love your honest feedback - ⭐ the repo, open an issue, tell me where it breaks.
athrvk
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vayu
Open-source API client with a native C++ load-testing engine. Postman-style requests + k6-level load tests in one local app
Vayu — REST/GraphQL Client and Native Load Tester, in One Desktop App
Build a request like you do in Postman. Load test the same endpoint at tens of thousands of requests per second — driven by a native C++ engine. Fully local. No account, no cloud, no quotas.
Vayu is a free, open source desktop app for Windows, macOS, and Linux that merges two tools API teams normally split: a full REST + GraphQL request builder with collections, environments, and scripting, and a high-throughput load tester powered by a C++20 engine. The request UI will feel familiar coming from Postman or Insomnia — but underneath, a native event loop pushes load-test throughput that Electron + Node.js clients cannot reach, with every byte staying on your machine.
See it in action
The load-test dashboard. Throughput, latency percentiles, and error counters stream live from the C++ engine while the UI stays responsive.
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