API Performance Testing

Reuse your API tests
as performance tests.

Karate is the only open-source tool that lets you reuse your functional API tests as performance tests. Write tests once, run them at scale with Gatling under the hood — and get the same fuzzy assertions validating every response, even under load.

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UserPerfTest.java 
// Reuse your existing Karate feature
// file as a Gatling performance test
class UserPerfTest extends Simulation {

  val usersFeature = karateFeature(
    "classpath:features/users.feature")

  val scn = scenario("users").exec(usersFeature)

  setUp(
    scn.inject(
      rampUsers(100).during(10),
      constantUsersPerSec(50)
        .during(60)
    )
  ).assertions(
    global.responseTime.max.lt(2000),
    global.successfulRequests.percent.gt(99)
  )
}

Features

Write once, test everywhere

The same feature files that validate your functional tests also drive your load tests — with full assertions, rich reporting, and zero test duplication.

Test Reuse

Point Gatling at your existing Karate .feature files. No new scripts, no duplication — functional and perf tests stay in sync automatically.

Assertions Under Load

Unlike plain Gatling or JMeter, Karate validates every response against your fuzzy JSON matchers — so a degraded API returning 200-with-wrong-body fails your perf test too.

Rich HTML Reports

Full Gatling reporting built in: percentile latencies, error breakdowns, and failure line numbers so you know if you hit an infra bottleneck or an assertion mismatch.

CI/CD Native

Continuous perf testing out of the box. Hook into Jenkins, GitHub Actions, GitLab CI, or TeamCity — same pipeline as your functional tests, no separate perf stage.

Maven & Gradle

Works with any JVM project. Drop the karate-gatling dependency into your pom.xml or build.gradle and you're done.

Java Interop

Call Java utilities from your perf tests for custom data generation, auth flows, or database seeding — all with full access to your existing codebase and classpath.

Built on proven infrastructure

Gatling Maven Gradle Jenkins GitHub Actions GitLab CI Docker

Comparison

Karate vs traditional load testing

How reusable, assertion-driven perf testing compares to tools built for raw load.

Capability Karate Gatling (standalone) JMeter
Reuse functional tests as perf tests Yes — zero rewrites No No
Fuzzy assertions under load Built-in Basic status checks Basic status checks
No-code / Low-code scripts Gherkin syntax Scala DSL XML + UI
HTML reporting Yes — Gatling-powered Yes Yes (basic)
CI/CD pipeline integration Native Via Maven/SBT Via plugins
Java interop Full Scala only Limited
Learning curve Hours Days (Scala required) Days (UI + XML)
Open source Yes — MIT Yes Yes

Note: by default, Karate caps at ~30 RPS without thread-pool tuning — configurable for higher loads. See the docs for production setups.

Stop writing the same tests twice.

One syntax. Two use cases. Functional tests by day, performance tests by night — all from the same feature files.

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