k6
Modern load testing tool written in Go with JavaScript test scripts. Write test scenarios in JavaScript (TypeScript supported), run them against HTTP endpoints, WebSockets, or gRPC services. Outputs performance metrics (response times, throughput, error rates) to stdout, Grafana Cloud, InfluxDB, or Prometheus. Used for performance benchmarking agent APIs and LLM endpoints.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
Load testing tool that generates high traffic — only run against systems you own or have permission to test. k6 Cloud results may contain sensitive response data — review data retention policy.
⚡ Reliability
Best When
You need to performance test HTTP APIs, agent backends, or LLM endpoints with realistic concurrent load and metrics integration with Grafana/Prometheus.
Avoid When
You need browser-based load testing or multi-protocol support — use Locust for Python-native load tests or Gatling for JVM-based testing.
Use Cases
- • Load test agent HTTP API endpoints to measure throughput, latency percentiles, and error rates under realistic concurrent load
- • Performance benchmark LLM API response times under simulated multi-user agent workloads
- • Verify agent service SLOs under load with k6 thresholds that fail if response times or error rates exceed limits
- • Stress test agent WebSocket connections and streaming endpoints at scale
- • Integrate performance tests into agent CI/CD pipelines with k6 cloud or local execution with pass/fail thresholds
Not For
- • Functional E2E browser testing — use Playwright or Cypress for browser-based functional testing
- • Protocol testing beyond HTTP/WebSocket/gRPC — k6 is focused on these protocols
- • Very high-scale distributed load testing without k6 Cloud — single-machine k6 has memory limits; k6 Cloud distributes load
Interface
Authentication
k6 Cloud requires API token. Local k6 execution is free with no auth. k6 extension ecosystem for cloud backends.
Pricing
Apache 2.0 license for k6 CLI. k6 Cloud is Grafana Labs' managed service for distributed load testing.
Agent Metadata
Known Gotchas
- ⚠ k6 uses a custom JavaScript runtime (goja, not Node.js) — many Node.js APIs (fs, process.env, require) are unavailable in k6 scripts; use k6 modules (k6/http, k6/metrics) instead
- ⚠ Virtual Users (VUs) are goroutines, not processes — each VU runs the same script concurrently; shared state between VUs requires k6's SharedArray for efficient data sharing
- ⚠ k6 metrics are summarized after the test — real-time streaming requires k6 cloud or an output destination (influxdb, prometheus); local stdout only shows end-of-test summary
- ⚠ HTTP keep-alive is enabled by default — connections are reused between requests which is realistic for most APIs but may not represent stateless API call patterns
- ⚠ k6 thresholds abort the test if exceeded only when abortOnFail: true is set — by default thresholds mark the test as failed but don't stop execution early
- ⚠ sleep() calls are required in VU scripts to simulate realistic user think time — without sleep(), k6 hammers the endpoint as fast as possible which may not reflect realistic usage
Alternatives
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for k6.
Scores are editorial opinions as of 2026-03-06.