Jazzer vs Schemathesis

Jazzer is a free, coverage-guided fuzzer for JVM applications, running in-process and based on libFuzzer. It supports Java, Kotlin, Scala, and Clojure targets, as well as JNI and native libraries. With JUnit 5.9.0 or newer, fuzz tests can run alongside regular unit tests. The @FuzzTest annotation lets Jazzer generate and mutate method inputs, including primitives, strings, arrays, and standard library classes. JUnit fuzz tests can use saved crashing inputs in regression mode or generate and mutate inputs to explore coverage. Built-in sanitizers detect Java security issues such as SSRF, file path traversal, and OS command injection, and provide feedback to guide fuzzing. The README documents use with Maven, Gradle, and Bazel. Jazzer can also run as a standalone binary or through its Java main class. Supported systems are Linux x86_64 and arm64, macOS 12 or newer on x86_64 and arm64, and Windows x86_64. The jazzer-junit package is available on Maven Central, and the repository identifies the project as licensed under Apache-2.0.

Schemathesis generates property-based tests from OpenAPI and GraphQL schemas to help engineers find API bugs. Its cases probe boundary values, type mismatches and constraint violations, and it validates API responses against the OpenAPI specification. For multi-step workflows, it chains operations using links inferred from a schema. During a run, it can learn validation rules, resource IDs and authentication requirements from server responses, then reuse them. Users can add Python checks for business rules alongside built-in checks. It supports OpenAPI 2.0, 3.0, 3.1 and 3.2, plus GraphQL schemas. Authentication options include Bearer tokens, Basic authentication and API keys, with environment variable substitution and Python hooks for dynamic flows. Integrations include a GitHub Action, Docker image, pip or uvx installation, and pytest. Reports can be exported as JUnit, VCR, HAR, NDJSON, JSON or Allure; failures can also be saved with curl commands for replay. The tool is self-hosted and licensed under MIT.