Pick the tool that matches your team's language, then start with one critical API journey. k6 uses JavaScript or TypeScript, runs from the command line, and turns thresholds into a build pass or fail. JMeter has a desktop GUI, the widest protocol coverage (JDBC, JMS, LDAP) and a thread-per-user model that needs more resources. Gatling uses a Scala, Java or Kotlin DSL and is known for high virtual-user density and built-in HTML reports. Run a single-user smoke test first, then a baseline load test, and add thresholds in CI once you know what normal looks like.

The core difference between k6 and JMeter is architecture:

| | Apache JMeter | Grafana k6 | | :--- | :--- | :--- | | Execution model | One JVM thread per virtual user | Each virtual user is its own JavaScript runtime, scheduled by the Go runtime | | Scripting | XML test plans, usually built in the GUI | JavaScript or TypeScript | | Memory per virtual user | Grows with the test plan and listeners | 1-5 MB for simple scripts, more with large modules or files | | CI fit | Needs plugins or wrapper scripts | A failed threshold exits with a non-zero code |

k6's own guidance is to measure memory on a small run and scale linearly, because the figure depends heavily on the script.

Sources: Vervali comparison, QASkills comparison, Grafana k6 course, k6: running large tests