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Fusillade vs k6: Why Teams Are Switching

10 min read

k6 has been the go-to open source load testing tool for many teams. But as performance requirements grow and cloud testing costs increase, an increasing number of engineering teams are evaluating alternatives. Here is how Fusillade compares to k6 across the dimensions that matter.

At a Glance

FeatureFusilladek6
EngineRust (tokio)Go (goja JS)
ScriptingJavaScript (global APIs)JavaScript (k6 modules)
Throughput (20K workers)165,017 RPS74,411 RPS
P95 Latency (20K)1.18 ms99.5 ms
Memory (20K workers)302 MB5,926 MB
Cloud Regions33 regionsGrafana Cloud k6
Protocol SupportHTTP, WebSocket, SSE, gRPC, MQTT, AMQPHTTP, WebSocket, gRPC
Browser TestingChromium (built-in)Chromium (extension)
LicenseAGPL v3AGPL v3
Cloud PricingFrom $0 (100 min/mo free)Free tier + paid plans

Architecture: Rust vs Go

k6 is written in Go and uses goja, a JavaScript interpreter written in Go. Each virtual user runs inside a goroutine with its own goja runtime. While Go's goroutines are lightweight compared to OS threads, each goja VM instance carries significant memory overhead and the JS-to-Go bridge introduces latency on every HTTP call.

Fusillade is built in Rust on top of tokio with a custom QuickJS-based JavaScript engine. HTTP requests are executed directly through hyper with zero-copy buffer management. Each VU is a tokio task -- orders of magnitude lighter than a goja VM.

The architectural difference explains Fusillade's 84x lower latency and 20x lower memory usage. Fusillade's Rust engine doesn't have a garbage collector pausing execution, doesn't marshal data between language runtimes, and uses async I/O natively rather than through a compatibility layer. Each worker gets its own independent connection, making it a true concurrent user simulation.

Performance Deep Dive

The benchmark numbers above come from controlled tests on identical hardware. Here is what those numbers mean in practice.

Throughput
2.2x faster

165,017 vs 74,411 RPS with 20,000 concurrent workers on the same machine.

Latency
84x lower P95

1.18 ms vs 99.5 ms. Sub-millisecond overhead means accurate measurements.

Memory
20x less RAM

302 MB vs 5,926 MB for 20K workers. k6 needs nearly 6 GB.

Install Fusillade and run your own benchmarks to see the difference firsthand.

Scripting: Familiar but Different

Both tools use JavaScript for test scripts, but the API surface differs. k6 uses a module-based import system where you import from k6/http, k6/ws, etc. Fusillade exposes global APIs -- no imports needed for built-in functionality.

Fusillade
// No imports needed
export const options = {
vus: 100,
duration: "30s",
};
export default function() {
http.get("https://api.example.com");
sleep(0.1);
}
k6
import http from 'k6/http';
import { sleep } from 'k6';
export const options = {
vus: 100,
duration: '30s',
};
export default function() {
http.get('https://api.example.com');
sleep(0.1);
}

Fusillade's global API approach means less boilerplate and no need to remember import paths. The http, ws, check, sleep, and other APIs are available everywhere. Local imports work for your own modules -- you just don't need them for the built-in APIs.

If you are migrating from k6, the concepts are identical. Remove the k6 imports, keep your test logic, and your scripts work as-is.

Cloud Execution

k6's cloud offering is Grafana Cloud k6, which provides managed load zones and various pricing tiers. Fusillade Cloud provides 33 global regions with workers that spin up on-demand and are destroyed after each test.

The key difference is billing model. Grafana Cloud k6 pricing scales with VU count and test duration. Fusillade bills by worker-minutes: straightforward, predictable, and the free tier includes 100 minutes per month with up to 1,000 workers.

For multi-region testing, Fusillade lets you distribute workers across any combination of 33 regions. See our distributed load testing guide for details on multi-region test design.

Protocol Support

Both tools support HTTP/1.1, HTTP/2, WebSocket, and gRPC. Fusillade additionally supports SSE (Server-Sent Events), MQTT, and AMQP natively -- protocols that are increasingly important for real-time applications and event-driven architectures.

ProtocolFusilladek6
HTTP/1.1 & HTTP/2✓✓
WebSocket✓✓
gRPC✓✓
SSE✓✗
MQTT✓✗
AMQP✓✗

When k6 Might Be the Right Choice

k6 has a large ecosystem and mature Grafana integration. If your team already uses Grafana for observability and wants unified dashboards, k6's native Grafana integration is convenient. k6 also has a larger library of community extensions through its xk6 system.

That said, for teams where raw performance, lower cloud costs, and broader protocol support matter, Fusillade is the stronger choice. And since both tools use JavaScript for scripting, migrating existing tests is straightforward.

Try Fusillade free

100 minutes of cloud testing per month. No credit card required. Migrate your k6 scripts in minutes.

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