k6

Load testing tool with JavaScript tests on a Go runtime, now owned by Grafana Labs

As of 30 August 2026, k6 is free to use. A command line load testing tool where tests are ES6 JavaScript executed by a Go engine, so npm packages generally do not work. Softwr lists it under Testing. k6 is made by Grafana Labs, available on Windows, macOS, Linux, Self-hosted.

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Overview

What k6 does

k6 runs performance tests defined as JavaScript modules: virtual users execute a scripted scenario against HTTP, WebSocket, gRPC or browser targets, and pass or fail is decided by thresholds declared in the test rather than read off a chart afterwards. The core tool is AGPL-3.0 licensed, runs as a single binary, and prints results to the terminal or streams metrics to Prometheus, InfluxDB or Grafana Cloud. The runtime is the detail that decides adoption. Tests are written in JavaScript but executed by a JavaScript engine embedded in Go, not by Node.js, and there is no browser DOM in a protocol test. Practically this means npm packages usually cannot be required, anything depending on Node built-ins fails, and shared helper code has to be bundled to plain JavaScript first. Teams that expected to reuse their existing Node test utilities find this out on day one. In exchange the tool generates far more load per machine than a Node-based runner, which is why thousands of virtual users on a laptop is realistic. k6 was built by Load Impact and acquired by Grafana Labs, and that ownership shapes what gets built. Investment goes to the parts that make k6 a data source for Grafana: cloud test results, dashboards, correlation with existing observability data. Anyone selecting it as a standalone load testing tool should expect the standalone path to stay functional but receive less attention than the Grafana Cloud integration, and the cloud service bills by virtual user hour, a unit that makes long soak tests disproportionately expensive compared with short high-concurrency spikes.

What people use it for

Gating a deployment pipeline on a threshold such as 95th percentile latency under a defined arrival rate
Generating tens of thousands of requests per second from a small number of machines without a load generator fleet
Testing gRPC and WebSocket services with the same tooling and thresholds used for HTTP endpoints
Correlating a load test against existing dashboards for an organisation already running Grafana and Prometheus

Where it falls short

Concrete and checkable, so you can decide whether any of them matter to you. This is the half of a review a vendor will not write about k6.

Tests run on a JavaScript engine embedded in Go rather than on Node.js, so npm packages, Node built-ins and existing shared test utilities generally do not work without being bundled to plain JavaScript, and often not even then.
The open source binary runs on a single machine, so distributed load requires the Kubernetes operator or the cloud service, and the operator is infrastructure your team has to run and debug.
The AGPL-3.0 licence on the core requires legal review at any company that intends to embed k6 in a product it distributes or offers as a service, which is a slower path than a permissively licensed tool.
There is no result storage in the open source tool, so trend history means standing up Prometheus, InfluxDB or Grafana Cloud before load testing produces anything comparable over time.
Since the Grafana Labs acquisition the roadmap serves the Grafana observability stack, so a buyer choosing k6 as a standalone tool should expect the standalone experience to receive less investment than the cloud and dashboard integration.
Grafana Cloud billing is by virtual user hour, so a long soak test at modest concurrency costs far more than its peak load suggests, and cost planning has to be done in virtual user hours rather than in test runs.

Cross-shopped

What people choose instead of k6

Each pairing was judged by two reviewers asking whether a buyer would genuinely weigh the two against each other. The ones that failed were deleted rather than published.

k6vs
Playwright
Playwright: If the requirement is functional browser testing rather than measuring how a service behaves under concurrent load
k6vs
GitHub Actions
GitHub Actions: If you only need to run existing performance scripts on a schedule and store the output as CI artefacts

Pricing

What k6 costs

Taken from the vendor's own pricing page. Prices move, so check before you buy.

k6 OSS

Free

AGPL-3.0 licence
Full test engine, no virtual user limits
Runs on one machine unless distributed yourself
No hosted result storage

Grafana Cloud free tier

Free

Includes a monthly allowance of virtual user hours
Hosted test results and dashboards
Shared with the rest of the Grafana Cloud free tier

Grafana Cloud k6

On request

Billed by virtual user hours consumed
Load generation from multiple regions
Retained test history and comparison
Pricing on application beyond the included allowance

Capabilities

Features

JavaScript test scripts
Scenarios written as ES6 modules and run by a Go-embedded JavaScript engine, not Node.js
Thresholds and checks
Pass or fail criteria declared in the test so a load run can gate a CI pipeline
Protocol coverage
HTTP/1.1, HTTP/2, WebSocket, gRPC and Redis targets from the same script
Browser module
Drives Chromium over the DevTools protocol to measure real page metrics alongside protocol load
Executors
Constant arrival rate, ramping, shared iterations and other load profiles instead of a single ramp model
xk6 extensions
Custom protocols and outputs compiled into a bespoke k6 binary in Go
Metrics output
Streams to Prometheus, InfluxDB, Datadog, New Relic or Grafana Cloud for retention
Kubernetes operator
Distributes a test across pods for load beyond one machine without the cloud service

Answered, with sources

Questions people ask

Each answer names the page it came from, so you can check it rather than take our word for it.

Can I use npm packages in a k6 test?

Usually not. Scripts run on a Go-embedded JavaScript engine with no Node.js runtime, so packages depending on Node built-ins fail and pure JavaScript libraries must be bundled first.

Is k6 free?

The core tool is free under AGPL-3.0 with no virtual user limits. Grafana Cloud k6 is a paid service billed by virtual user hours, with a free monthly allowance.

Does the Grafana acquisition affect the open source tool?

The tool remains open source and maintained, but investment is directed at making it a data source for Grafana, so standalone use is supported rather than prioritised.

Can k6 replace a browser testing tool?

No. The browser module measures page-level metrics under load, but functional browser testing belongs in Playwright or a similar tool.

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Softwr does not host reviews and shows no star rating for k6, because a rating we did not collect is not ours to publish. What is here is the pricing and platform detail from the vendor’s own pages, limitations we could state concretely, and alternatives a reviewer confirmed people weigh against it. Tell us if any of it is wrong.

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