Locust vs Grafana k6

Free and open source

From $19 per month (Grafana Cloud Pro platform fee; k6 usage is billed on top)

Free and open source. You pay in engineering time and CI minutes.

Self-hosted is free and unlimited. On Grafana Cloud the free tier includes 500 virtual-user-hours a month, then k6 bills from $0.150 per virtual-user-hour on top of the $19 Pro platform fee — the VU-hours, not the platform fee, are where budgets go.

Everything, self-hosted

The k6 CLI is fully open source with no virtual-user limits when self-run.

Widely used

OSS community · since 2011

Category standard

Grafana Labs · since 2016

• Test scenarios are plain Python, so any logic is expressible without workarounds.
• Distributed mode is conceptually simple and works well on Kubernetes.
• Live web UI is useful during an exploratory ramp-up.

• Excellent resource efficiency — thousands of virtual users from one modest machine.
• Thresholds make performance a build gate rather than a report nobody reads.
• Native Grafana and Prometheus integration ties load results to server-side metrics.

• Python's per-user overhead is higher than k6 or Gatling; big loads need more machines.
• Reporting is basic — plan on exporting to Grafana.
• HTTP-centric; other protocols require writing your own client.

• The JavaScript runtime is not Node — no npm modules unless bundled, which surprises people.
• Browser-level load testing exists but is much heavier and less mature than protocol-level testing.
• Distributed execution requires either the cloud product or your own orchestration.

Python teams who want load scenarios expressed in their own language.

Engineering teams that want performance regression tests running in CI.