OPNsense is a firewall and network security appliance that provides the GUI, API, and systems backend for an open source firewall platform built on FreeBSD.
The project addresses the need for a modern, extensible firewall solution by offering a complete management interface and backend system. It handles core firewall functionality including routing, VPN, intrusion prevention, proxy services, traffic shaping, and captive portal capabilities. The codebase is structured around a documented architecture designed to support gradual evolution rather than disruptive rewrites, with a build system intended to be accessible to developers who want to contribute or customize the software for their own use.
OPNsense suits organizations and individuals seeking an open source alternative to proprietary firewalls, particularly those comfortable with FreeBSD-based systems. The project welcomes contributions through testing, bug reports, and pull requests. Developers working on the codebase have access to a range of development tools including linting, style checking with PSR12 and PEP8 standards, and automated sanitizers. The build process is designed to be straightforward, with a Makefile providing targets for packaging, updating, upgrading, and collecting changes from running systems. An optional debug plugin is available to provide additional development tools within an OPNsense VM environment.
The project maintains active code quality monitoring through automated scanning. Development follows a structured contribution process documented in the repository, with all contributions required to be licensed under the 2-Clause BSD license. The codebase is written primarily in PHP for the management layer, with supporting build infrastructure and tooling available in a separate tools repository.
