Why use Karate for performance testing instead of a dedicated tool like JMeter alone?

JMeter and similar dedicated performance tools are powerful but require building and maintaining a separate set of test scripts, typically in a different format or UI than the functional API tests already exist as, which means the two suites can drift apart as the API evolves.

Karate's Gatling integration lets the exact same feature files already used for functional testing be executed under load, so there's only one place request logic, headers, and payloads are defined and maintained. When an endpoint's request shape changes, updating the one feature file keeps both the functional test and the performance test correct, rather than needing the same change applied in two unrelated tools.

This isn't a universal replacement for a dedicated performance tool: JMeter has a much larger ecosystem of protocol support, plugins, and specialized load-testing features built up over a longer history, so teams with complex, large-scale performance-testing needs beyond what Gatling covers may still reach for JMeter or a similar dedicated tool specifically for that purpose, while using Karate for the functional layer regardless.