The best free firewall software depends on your platform: Windows Firewall is built in and on by default, TinyWall and ZoneAlarm Free Firewall add more control on Windows, LuLu covers Mac, UFW and netfilter cover Linux, and pfSense runs on a dedicated box. GlassWire's free tier is a network monitor; its firewall controls sit behind Premium.
I've sorted this by platform, because a firewall is only useful if it runs on the machine you're trying to protect. Every item below says what its own page states about cost and licence, as of Nov 2026. Eight made the cut. One popular name, GlassWire, sits in its own section at the end, because calling its free tier a free firewall would be misleading.
A quick reality check first: most people already have one. If you're on Windows, you've got a firewall running right now. The question isn't usually whether you need free firewall software, it's whether you want more control than the built-in one gives you.
| Firewall | Platform | What its own page says about cost or licence |
|---|---|---|
| Windows Firewall | Windows | Included with the operating system, enabled by default |
| TinyWall | Windows | Completely free, no ads, no upgrades |
| ZoneAlarm Free Firewall | Windows 11 and 10 | Download Free |
| Comodo Firewall | Windows | Provides free firewall protection |
| LuLu | Mac | Free, open-source firewall |
| UFW (with Gufw) | Ubuntu Linux | Ubuntu's default firewall configuration tool |
| netfilter (iptables, nftables) | Linux | GNU General Public License version 2 |
| pfSense | Router or appliance | Open source firewall |
Windows: four free options
Windows Firewall
Microsoft's Windows Firewall overview describes it as a host-based firewall that's included with the operating system and enabled by default on all Windows editions. Its default behaviour is to block all incoming traffic unless it's solicited or matches a rule, and to allow all outgoing traffic unless it matches a rule. It also switches profiles, applying stricter public network settings on coffee shop Wi-Fi than on your home network. For most home users, this is enough.
TinyWall
TinyWall calls itself a free, lightweight and non-intrusive firewall for Windows, and its page goes further than most: 100% free, no ads, no artificial limitations, no upgrades, and no data collection or telemetry. It adds tampering protection, blocklists, temporary firewall rules and boot-time filtering. Version 3.6 brought wildcard support and block reason attribution. If Windows Firewall feels too hidden, this is the one I'd try first.
ZoneAlarm Free Firewall
ZoneAlarm's page says its free firewall is compatible with Windows 11 and 10 and protects against inbound and outbound attacks, blocks unwanted traffic and controls which programs reach the internet. Expect upsells: the same page promotes paid suites and renewal offers.
Comodo Firewall
Comodo's firewall page says it provides free firewall protection, backed by a safe-list of over two million known PC-friendly files and apps, a Training Mode that creates allow rules automatically, and an Auto Sandbox for untrusted programs. Comodo's firewall page doesn't list supported Windows versions in its text, and the same page also sells paid Internet Security packages, so read each download button carefully.
Mac: LuLu
LuLu, from Objective-See, is described on its own page as a free, open-source firewall that blocks unknown outgoing connections. That's the catch worth knowing: LuLu only monitors outgoing traffic, so its rules only apply to outgoing connections. It needs macOS 10.15 or later, and if you're on Sequoia, Objective-See says to be on at least macOS 15.3, because Apple broke parts of networking in the first release of macOS 15.0. It also bundles Netiquette, a network monitor, if you want to see live connections. It's the one I'd put on any Mac where you care about what your apps phone home to.
Linux: UFW and netfilter
On Ubuntu, the Ubuntu Wiki says the default firewall configuration tool is ufw, short for Uncomplicated Firewall. It was built to make iptables easier, and it creates IPv4 or IPv6 host-based firewall rules. Here's the bit people miss: by default UFW is disabled. Having it installed doesn't mean it's protecting you, so switch it on. If you'd rather click than type, Gufw is a graphical frontend for it.
Underneath sits netfilter, the project behind iptables and nftables. Netfilter.org says it provides packet filtering for the Linux 2.4.x and later kernel series, and that its kernel software is released under the GNU General Public License version 2. Most people won't touch it directly; tools like UFW write the rules for you.
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Router or appliance: pfSense
pfSense bills itself as the world's most trusted open source firewall, used by thousands of enterprises, and the site has a Download link for the software. You'd run it on a spare computer or a dedicated box to protect a whole network rather than one device. Be aware the same home page sells cloud instances and Netgate appliances running pfSense Plus, so make sure you're on the open source download rather than a paid product. This is the pick for a small office that wants one firewall in front of everything, as part of taking information security seriously.
GlassWire: the free tier is a monitor
GlassWire comes up in every list like this, so let's be straight about it. Its own pricing page describes the free tier as being for users with basic network monitoring needs. The comparison grid does list firewall controls, such as Click-to-Block Firewall and Bidirectional Firewall Control, but the page pushes Premium for the full feature set. So the free version is useful for seeing which apps use your connection, but it's not a free firewall in the sense of the eight above. I've left it out of the count on purpose.
Which one I'd install
On Windows, leave Windows Firewall on and add TinyWall if you want visible control over which programs can connect. On a Mac, install LuLu. On Ubuntu, enable UFW, because it's off until you do. For a business network, put pfSense in front of the router. And if you handle sensitive board or client documents, a firewall is only one layer; secure board portal security matters just as much.
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Quick answers
Is Windows Firewall good enough?
For most home users, yes. Microsoft says it's included with Windows and enabled by default, blocking unsolicited incoming traffic while allowing outgoing traffic unless a rule says otherwise.
What's the best free firewall for Mac?
LuLu from Objective-See is a free, open-source firewall for macOS 10.15 or later. It only filters outgoing connections.
Is UFW on by default in Ubuntu?
No. The Ubuntu Wiki says UFW is disabled by default, so you need to enable it before it protects anything.
Is GlassWire a firewall?
GlassWire's pricing page lists firewall controls, but pitches its free tier at basic network monitoring needs and pushes Premium for the full feature set. Treat the free version as a monitor rather than a free firewall.
