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safing/portmaster

Free, open-source application firewall for Windows and Linux that monitors and controls each app's network traffic, with built-in secure DNS and tracker blocking.

Open-source alternative to:Little SnitchGlassWire

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What is it?

Portmaster is a desktop application firewall that sits between your applications and the network. It records which app opens which connection and lets you allow or block each one, with defaults meant to improve privacy without manual setup. Users can also set global rules, per-app rules, and rules based on domain, IP, or country.

On Linux it hooks into the network stack via nfqueue and uses eBPF and /proc to identify connection owners. On Windows it relies on a kernel driver (WFP) and the IP Helper API. DNS queries are rerouted through the firewall and resolved over DoT or DoH, and filter lists block known malware, ad, and tracker domains. The core runs as a system service, while the UI runs in the user session.

Paid tiers add network history stored locally and searchable, per-app bandwidth monitoring, and SPN, a multi-hop privacy network positioned between VPN and Tor. The project is GPL-3.0 licensed and developed in Austria.

Key features

  • 01Monitors network connections and attributes them to individual applications.
  • 02Blocks or allows traffic by app, domain, IP, country, or network scope.
  • 03Reroutes DNS queries through secure DoT/DoH resolvers.
  • 04Blocks malware, ad, and tracker domains using filter lists.
  • 05Runs entirely locally with automatically signed and applied updates.

Use cases

  • Stopping apps on a Windows or Linux desktop from phoning home unnoticed.
  • Applying one privacy baseline across all applications without per-app configuration.
  • Inspecting which domains and services a given program contacts.
  • Enforcing encrypted DNS on a personal computer.

Quick start

  1. 1

    Download Portmaster for free from the official download page

  2. 2

    Install Earthly CLI to build from source

  3. 3

    Install Docker Engine as a build prerequisite

  4. 4

    Build the release with Earthly, then find artifacts in ./dist

    earthly +release

Things to know

  • Supports only Windows and Linux, not macOS.
  • Some advanced features such as network history, bandwidth usage and SPN require a paid plan.
  • The main UI still uses Electron, and the README says the build process is a work in progress.

In collections

Privacy & local-first toolsDesktop GUI apps & toolkits

Topics

#privacy#firewall#dns#networking#security-tools#desktop#ad-blocking#go#application-firewall#golang

FAQ

What is portmaster?
Free, open-source application firewall for Windows and Linux that monitors and controls each app's network traffic, with built-in secure DNS and tracker blocking. Portmaster is a desktop application firewall that sits between your applications and the network. It records which app opens which connection and lets you allow or block each one, with defaults meant to improve privacy without manual setup. Users can also set global rules, per-app rules, and rules based on domain, IP, or country.
Is portmaster free to use? What license does it have?
portmaster is open source under the GPL-3.0 license. Check the license terms before using it in commercial products.
Is portmaster still maintained?
Actively maintained. The last commit to portmaster was on Oct 21, 2026.
What can I use portmaster for?
Stopping apps on a Windows or Linux desktop from phoning home unnoticed. Applying one privacy baseline across all applications without per-app configuration. Inspecting which domains and services a given program contacts. Enforcing encrypted DNS on a personal computer.
How do I install portmaster?
Download Portmaster for free from the official download page Install Earthly CLI to build from source Install Docker Engine as a build prerequisite Build the release with Earthly, then find artifacts in ./dist: earthly +release
Where can I get portmaster?
The source code and installation instructions are on GitHub: https://github.com/safing/portmaster

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