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Jazzer

Jazzer is Code Intelligence's Apache-2.0 coverage-guided, in-process fuzzer for the JVM, based on libFuzzer, with JUnit integration and bug detectors.

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Introduction

Jazzer is a coverage-guided, in-process fuzzer for the JVM platform from Code Intelligence, built on libFuzzer. It brings libFuzzer-style fuzzing to Java and other JVM languages, and fuzz tests can be written as JUnit tests.

The source code is at CodeIntelligenceTesting/jazzer on GitHub under the Apache-2.0 licence, with about 1,300 stars; the most recent commit was on 9 November 2026.

Features

  1. JUnit fuzz tests: @FuzzTest style integration.
  2. Coverage-guided: libFuzzer engine.
  3. Bug detectors: Detect injection and other issues at runtime.
  4. Structured inputs: Helpers for typed data.
  5. OSS-Fuzz support: Used for JVM projects in OSS-Fuzz.

Pros

  1. Free to use: Open source under Apache-2.0.
  2. Maintained: Commits as recent as 9 November 2026.

Cons

  1. JVM only: Single platform.
  2. Harness design: Good targets take thought.

Add the Jazzer JUnit dependency, then write:

@FuzzTest
void fuzz(FuzzedDataProvider data) {
    MyParser.parse(data.consumeRemainingAsString());
}

Resources:

Pricing

Jazzer is free and open source under the Apache-2.0 licence.

  1. Java teams adding fuzzing to unit tests.
  2. Library maintainers hardening parsers.
  3. Not a fit for non-JVM code.

Conclusion

Jazzer brings practical coverage-guided fuzzing to the JVM through JUnit.

Alternatives

Other tools on CheckOps that cover similar ground. Open a page, or compare one with Jazzer side by side.