Fuzzilli

7.0easy start · #7 of 27
in Fuzz Testing Software

Free to practise onyes
Free trialnot on record
Well documentedyes
Runs where you worknot on record

Runs on Linux, Mac, self-hosted.

Fuzzilli is ranked #7 of 27 in fuzz testing software on The Geeks Club. It runs on Linux, macOS, Self-hosted. There is a free plan.

Fuzzilli plans and pricing

All plans

Fuzzilli Free Apache-2.0 licensed source code · requires building the fuzzer and a supported, instrumented JavaScript engine github.com · 4 Oct 2026

Compared on fuzz testing software

Input generation methods: mutation, generation, hybrid
Target types: JavaScript programs and JavaScript engines/interpreters
Coverage guidance: Yes
Crash triage: Yes
Execution mode: hybrid
Supported languages: JavaScript
CI/CD support: Yes

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The record

What it does: Fuzzilli is a coverage-guided fuzzer for dynamic language interpreters, built around a custom intermediate language called FuzzIL that can be mutated and translated to JavaScript.
Mutations: Its documented mutators can change data flow, generate or splice code, combine corpus programs, and modify operation parameters.
Fuzzer components: The listed components include a mutation fuzzer, script runner, corpus, environment, minimizer, evaluator, and lifter.
Execution: Fuzzilli uses a read-eval-print-reset-loop mode in which a modified target engine accepts scripts over pipes or shared memory, executes them, resets, and waits for the next script.
Scaling: Multiple instances can synchronize within one process or over a TCP-based protocol, allowing scaling across cores and machines.
Supported targets: The repository lists JavaScriptCore, JerryScript, QuickJS, QtJS, Serenity, SpiderMonkey, V8, XS, Duktape, and njs target directories.
Build requirements: The usage instructions call for compiling a supported JavaScript engine with coverage instrumentation using clang 4.0 or later, then building Fuzzilli with Swift Package Manager.
Deployment: The project says Fuzzilli and supported engines can be built and run inside Docker and on Google Compute Engine.
Cloud tooling: Its Cloud directory contains Docker scripts and files, Google Compute Engine setup and teardown scripts, and rudimentary crash triaging.
Security results: The repository’s bug showcase lists security issues found with Fuzzilli across engines including WebKit/JavaScriptCore, SpiderMonkey, V8, Duktape, JerryScript, and Hermes.
Security disclosure: The project asks users to send a short note, possibly with a CVE number, or open a pull request to have a vulnerability found with Fuzzilli considered for the bug showcase.
License: The repository identifies its license as Apache-2.0.
Support status: The repository states that Fuzzilli is not an officially supported Google product.
Intended users: The project describes Fuzzilli as a tool for fuzzing dynamic language interpreters and invites patches and other contributions.
Price from: Free

Where it ranks on The Geeks Club

Best Fuzz Testing Software in 2026#7 of 27

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Sources

github.com/googleprojectzero/fuzzilli· checked 3 Oct 2026
github.com/googleprojectzero/fuzzilli/tree/main/Ta· checked 3 Oct 2026
github.com/googleprojectzero/fuzzilli/tree/main/Cl· checked 3 Oct 2026
github.com/googleprojectzero/fuzzilli/blob/main/CO· checked 4 Oct 2026