Skip to content


Switch branches/tags

Name already in use

A tag already exists with the provided branch name. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Are you sure you want to create this branch?

Latest commit


Git stats


Failed to load latest commit information.
Latest commit message
Commit time

Spicy — Robust Parsers for Protocols & File Formats

Stable Development
Documentation Spicy Manual
Changelog Release Notes CHANGES
Build status Build status release Build status development


Spicy is a parser generator that makes it easy to create robust C++ parsers for network protocols, file formats, and more. Spicy is a bit like a "yacc for protocols", but it's much more than that: It's an all-in-one system enabling developers to write attributed grammars that describe both syntax and semantics of an input format using a single, unified language. Think of Spicy as a domain-specific scripting language for all your parsing needs.

The Spicy toolchain turns such grammars into efficient C++ parsing code that exposes an API to host applications for instantiating parsers, feeding them input, and retrieving their results. At runtime, parsing proceeds fully incrementally—and potentially highly concurrently—on input streams of arbitrary size. Compilation of Spicy parsers takes place either just-in-time at startup (through a C++ compiler); or ahead-of-time either by creating pre-compiled shared libraries, or by giving you generated C++ code that you can link into your application.

Spicy comes with a Zeek plugin that enables adding new protocol and file analyzers to Zeek without having to write any C++ code. You define the grammar, specify which Zeek events to generate, and Spicy takes care of the rest. There's also a Zeek analyzers package that provides Zeek with several new, Spicy-based analyzers.

See our collection of example grammars to get a sense of what Spicy looks like.


We provide pre-built Spicy binaries for several Linux platforms, as well as a Homebrew formula (and also binaries) for installation on macOS. You can also pull a Docker image from Docker Hub, or leverage one of several included Docker files as a starting point. Of course, you can also just build Spicy from source directly. See the installation instructions for more information on any of these options.


Please read the Spicy Manual, which provides the following sections:

Getting in touch

Having trouble using Spicy? Have ideas how to make Spicy better? We'd like to hear from you!


Spicy is open source and released under a BSD license, which allows for pretty much unrestricted use as long as you leave the license header in place. You fully own any parsers that Spicy generates from your grammars.


Spicy was originally developed as a research prototype at the International Computer Science Institute with funding from the U.S. National Science Foundation. Since then, Spicy has been rebuilt from the ground up by Corelight, which has contributed the new implementation to the Zeek Project.