The Nmap Licensing Model

The law sits in the fine print, but the source code tells a bigger story. Nmap, the open-source network scanning tool, is released under a unique dual-licensing model that blends the GNU General Public License (GPL) with additional usage terms. This model is designed to protect Nmap’s integrity, prevent misuse in proprietary scanners, and ensure the tool remains free for security research, education, and legitimate operational use.

At its core, Nmap’s license is GPLv2. That means you can run, study, share, and modify it, provided that any distributed modifications are also open under the same terms. The GPL helps guarantee freedom for the code and its users. But Nmap’s authors add important clauses that go beyond stock GPL. These clauses restrict the integration of Nmap or its code into proprietary products without permission. The goal is to stop companies from embedding Nmap’s engine into commercial scanners or closed-source security products without sharing their own source code.

This approach creates a balance. Developers and organizations can use Nmap freely for testing, security audits, and operational monitoring. Commercial vendors can also use it—but must either comply with the GPL’s reciprocity or obtain a separate commercial license from the Nmap Project. The commercial license removes the copyleft requirement, enabling proprietary use for a fee, while funding ongoing development.

The Nmap Licensing Model is notable for its clarity in defending open-source principles while still offering a path for legal, proprietary adoption. It’s a rare instance of an open-source project wielding licensing as both shield and revenue model. For teams integrating scanning into their products, ignoring these terms risks legal exposure and public scrutiny. For engineers and legal teams, understanding the GPL plus Nmap’s custom terms is non-negotiable before deployment.

Read the full license text on the official Nmap site. Then build something that complies, scales, and ships fast. You can see it live in minutes at hoop.dev.