k6, JMeter, Locust and Artillery are excellent at one question: how much traffic can the backend absorb. None of them answer the other half — whether the phone in a customer's hand can execute, lay out and paint your page without stalling. Redline is that half.
| Dimension | k6 / JMeter / Locust / Artillery | Redline |
|---|---|---|
| What it measures | Server throughput under concurrent virtual users | Device capability under a real rendering workload |
| Where it runs | CLI, cloud runners, your own infrastructure | The browser on the device you are holding |
| Setup | Scripts, scenarios, runners, often credits | Open a URL, press start, five seconds |
| Finds | Capacity limits, error rates, latency at scale | The slowest device your site still has to serve |
| Output | Percentile latency graphs | A device score, cohort ranking and AI fixes |
| Who runs it | SRE, platform, performance engineering | Frontend, QA, product — anyone with a phone |
A load test that passes at 10,000 virtual users tells you nothing about a four-year-old Android on a throttled network. Run the load test in CI against staging, and run Redline against the devices your analytics say your users actually own.
Run the device test