Best Open-Source Security Tools in 2026: What Is Free and What It Costs to Run
Ten open-source security tools checked for license terms, free-tier caps and the paid rules, support and hosting that come after the install.
Short answer: the license is free for all ten tools, but the bill arrives after the install. For a 25-person company with 12 developers, two Snort sensors on business rules and one self-run service, our scenario costs $5,406 a year before staff time, based on vendor prices verified on 10 October 2026. The largest line is Semgrep's Teams plan, which starts once the team passes 10 contributors. For network work, OPNsense, Zeek and Suricata carry no license fee.
Key facts10 tools compared: OPNsense, Zeek, Suricata, Falco, Trivy, Keycloak, OpenBao, Semgrep…
- 10 tools compared: OPNsense, Zeek, Suricata, Falco, Trivy, Keycloak, OpenBao, Semgrep, Velociraptor, Snort 3
- Zeek (best for: SOC teams that want searchable network logs and will write their own detection scripts): Free under a BSD license that the README says allows free use with virtually no restrictions
- Suricata (best for: Teams that want one open engine for intrusion detection and prevention and will tune the rules themselves): Free under GPL-2.0; no engine price; commercial ET PRO rules are separate, with no price shown
- Falco (best for: Platform teams running containers or Kubernetes that want an alert when a workload does something it should not): Free under Apache 2.0; a CNCF graduated project with no paid plan in its repository
Cyberpresso data: Toolradar tracks 855 security tools as of 10 October 2026, and 45% of them are free, freemium or open source. Free is common in this category, but the license terms differ, and the paid step often sits in rules, contributor caps or support.
This guide reads the license and the paid tier of ten open-source tools, then prices the stack for one company. Toolradar's profiles for Falco, Trivy and Keycloak carry the wider listing.
For free scanners and free SIEM tiers, read our free vulnerability scanners guide and free SIEM guide. Their main picks stay out of this top ten.
Top Picks
Based on features, real-world fit, and value for money.
OPNsense is a free, open-source firewall and routing platform. Its paid Business Edition adds a web application firewall, proxy access and an extended blocklist.
Free under a simplified 2-clause BSD/MIT license; Business Edition price not published on the site
Small offices that want a full firewall on their own hardware and can run its updates themselves.
Zeek watches network traffic and writes structured logs for connections, files and protocols that a SIEM can search. The core costs nothing to license.
Free under a BSD license that the README says allows free use with virtually no restrictions
SOC teams that want searchable network logs and will write their own detection scripts.
Suricata is an open-source network IDS, IPS and network security monitoring engine. The Open Information Security Foundation, a community nonprofit, owns it.
Free under GPL-2.0; no engine price; commercial ET PRO rules are separate, with no price shown
Teams that want one open engine for intrusion detection and prevention and will tune the rules themselves.
| Tool | Pricing | Best for |
|---|---|---|
| OPNsense | Free under a simplified 2-clause BSD/MIT license; Business Edition price not published on the site | Small offices that want a full firewall on their own hardware and can run its updates themselves. |
| Zeek | Free under a BSD license that the README says allows free use with virtually no restrictions | SOC teams that want searchable network logs and will write their own detection scripts. |
| Suricata | Free under GPL-2.0; no engine price; commercial ET PRO rules are separate, with no price shown | Teams that want one open engine for intrusion detection and prevention and will tune the rules themselves. |
| Falco | Free under Apache 2.0; a CNCF graduated project with no paid plan in its repository | Platform teams running containers or Kubernetes that want an alert when a workload does something it should not. |
| Trivy | Free under Apache-2.0; Aqua builds a product on Trivy, and the repository shows no price for it | Engineering teams that scan container images, code and infrastructure files in their build pipeline. |
| Keycloak | Free under Apache-2.0; the repository lists no support subscription or price | Teams that want self-hosted single sign-on and can run, patch and upgrade the server themselves. |
| OpenBao | Free under MPL-2.0; no price is listed on the project's pages | Teams that ran HashiCorp Vault and need a secrets manager under an open-source license. |
| Semgrep | Free Edition $0 for up to 10 contributors; Teams from $30 per contributor per month for Code | Small development teams with 10 or fewer contributors that want code scanning in CI at no cost. |
| Velociraptor | Free under AGPL-3.0; no paid plan or support price listed in the repository | Incident responders who want to hunt for evidence across many endpoints and can run their own server. |
| Snort 3 | Free GPL-2.0 engine; Business rules $399 per sensor a year; Personal $29.99 a year, not for companies | Companies that already run Snort and will buy the Business rule set for each sensor. |
Pricing read from each vendor's own pricing page, checked Oct 2026. 1 of 10 publishes prices for some plans and quotes the rest.
OPNsense
OPNsense is a free, open-source firewall and routing platform. Its paid Business Edition adds a web application firewall, proxy access and an extended blocklist.
- Pricing
- Free under a simplified 2-clause BSD/MIT license; Business Edition price not published on the site
Best for: Small offices that want a full firewall on their own hardware and can run its updates themselves.
Pros
- The platform is free to download and use under a simplified 2-clause license, and the site calls its sources open and verifiable.
- The firewall itself carries no license fee, so the budget moves to hardware, updates and staff time.
Cons
- The Business Edition price is not published, so a company cannot compare it on the site without asking for a quote.
- Threat feeds and rules are extra: the site describes ET PRO for Suricata rules and Q-Feeds threat intelligence as subscriptions, with no prices shown.
Zeek
Zeek watches network traffic and writes structured logs for connections, files and protocols that a SIEM can search. The core costs nothing to license.
- Pricing
- Free under a BSD license that the README says allows free use with virtually no restrictions
Best for: SOC teams that want searchable network logs and will write their own detection scripts.
Pros
- The README describes a BSD license with virtually no restrictions, so a company can run and change it without a license fee.
- Logs are structured by protocol, so the same fields can be searched across months of traffic.
Cons
- Zeek is a framework, not an alert console: the scripts, log storage and triage are your team's work.
- The repository lists no paid plan or support price, so the real cost is analyst time and the storage the logs need.
Suricata
Suricata is an open-source network IDS, IPS and network security monitoring engine. The Open Information Security Foundation, a community nonprofit, owns it.
- Pricing
- Free under GPL-2.0; no engine price; commercial ET PRO rules are separate, with no price shown
Best for: Teams that want one open engine for intrusion detection and prevention and will tune the rules themselves.
Pros
- Owned by the Open Information Security Foundation, a community-run nonprofit, according to its own site.
- One engine covers intrusion detection, intrusion prevention and network security monitoring.
Cons
- The rules decide the value, and the commercial ET PRO subscription is sold separately; OPNsense lists it with no price.
- The about page lists no support plan or price, so support is a separate decision for your team.
Falco
Falco is a runtime security tool for containers and Kubernetes. It alerts on suspicious system activity and is licensed Apache 2.0.
- Pricing
- Free under Apache 2.0; a CNCF graduated project with no paid plan in its repository
Best for: Platform teams running containers or Kubernetes that want an alert when a workload does something it should not.
Pros
- The repository states an Apache 2.0 license and that Falco is a graduated Cloud Native Computing Foundation project.
- It watches live workloads, so it catches behavior that a scan at build time cannot see.
Cons
- It only helps where workloads run in containers or Kubernetes, so a company with only servers and laptops gets little from it.
- Sysdig Secure uses Falco rules and is sold separately, so its price is left out of the scenario.
Trivy
Trivy is an Apache-2.0 scanner for container images, file systems and infrastructure-as-code, from Aqua Security.
- Pricing
- Free under Apache-2.0; Aqua builds a product on Trivy, and the repository shows no price for it
Best for: Engineering teams that scan container images, code and infrastructure files in their build pipeline.
Pros
- The repository shows an Apache-2.0 license and states no usage cap.
- It runs as a single tool in a build pipeline, so the scanning step needs no separate server.
Cons
- A scanner reports known issues; it does not run your triage, ticketing or patch workflow.
- The paid Aqua product is promoted in the repository with no price, so the step up cannot be costed.
Keycloak
Keycloak is an Apache-2.0 identity and access server for single sign-on, OpenID Connect and SAML logins.
- Pricing
- Free under Apache-2.0; the repository lists no support subscription or price
Best for: Teams that want self-hosted single sign-on and can run, patch and upgrade the server themselves.
Pros
- The repository shows an Apache-2.0 license, and its README names no user-count cap.
- One server handles OpenID Connect and SAML logins for several applications.
Cons
- The license is free, but the server, its database and each upgrade are the real cost, and they land on your team.
- The repository lists no support plan or price, so vendor support is a separate decision.
OpenBao
OpenBao is a community fork of HashiCorp Vault under the MPL-2.0 license, managed under the Linux Foundation's OpenSSF.
- Pricing
- Free under MPL-2.0; no price is listed on the project's pages
Best for: Teams that ran HashiCorp Vault and need a secrets manager under an open-source license.
Pros
- The repository states MPL-2.0, while Vault 1.15.0 and later are under the Business Source License.
- The project describes open-governance principles and sits in the Linux Foundation's OpenSSF, per its homepage.
Cons
- It is a fork, so feature and API match with Vault is not guaranteed; check the features you use before you migrate.
- Hosting, backups and key handling stay with your team, and no support price is published.
Semgrep
Semgrep's open-source engine finds code issues with pattern rules under LGPL-2.1. The hosted free plan stops at 10 contributors and 10 repositories.
- Pricing
- Free Edition $0 for up to 10 contributors; Teams from $30 per contributor per month for Code
Best for: Small development teams with 10 or fewer contributors that want code scanning in CI at no cost.
Pros
- The engine is LGPL-2.1 on GitHub, and the free edition includes Code and Supply Chain scanning for up to 10 contributors.
- Rules are written as readable patterns, so a developer can see what a finding matched.
Cons
- The 11th contributor moves a company onto a paid tier, and Secrets adds $15 per contributor per month on top of Code.
- A contributor is anyone who committed to a scanned private repository in the last 90 days, so the count can grow faster than headcount.
Velociraptor
Velociraptor is an open-source endpoint visibility and forensics tool under AGPL-3.0, used to query and collect evidence from many machines.
- Pricing
- Free under AGPL-3.0; no paid plan or support price listed in the repository
Best for: Incident responders who want to hunt for evidence across many endpoints and can run their own server.
Pros
- The AGPL-3.0 license is published in the repository, and an internal team can run it without a license fee.
- It is built to query and collect evidence from many endpoints from one console.
Cons
- AGPL-3.0 requires offering the source of a modified version to users who reach it over a network, so a changed build exposed to outsiders carries duties.
- No support plan or price is listed, so the server, upgrades and hunting queries sit with your team.
Snort 3
Snort 3 is an open-source intrusion detection engine under GPL-2.0. The paid rule sets are where the subscription bill sits.
- Pricing
- Free GPL-2.0 engine; Business rules $399 per sensor a year; Personal $29.99 a year, not for companies
Best for: Companies that already run Snort and will buy the Business rule set for each sensor.
Pros
- The engine is GPL-2.0 on GitHub, and the community ruleset is free for all users, per Snort's product page.
- Paying subscribers get new rules 30 days before registered free users, per the same page.
Cons
- The Personal set is for home networks or education only, so a company has to buy the Business set for each sensor.
- Free registered users get rules later than paying customers, which matters most for a new exploit.
What it is
An open-source security tool is software whose source code you can read, run and change under a published license. The license is the part that costs nothing. Running the tool costs hosting, rule sets or subscriptions, and staff time, and those costs set the real bill.
Six open-source licenses appear in this list.
Apache-2.0 and BSD licenses carry the fewest duties, and MPL-2.0 keeps changed files open. GPL-2.0, LGPL-2.1 and AGPL-3.0 add duties when you change or share the code, and AGPL adds a duty for modified software that users reach over a network.
The Business Source License on HashiCorp Vault is source-available, not open source, which is why it gets its own warning below.
Why it matters
The license tells you whether you may run the tool at all, the free tier tells you how far it stretches, and the paid add-ons set the bill. Snort shows the pattern.
Its community rules are free for all users, but a company that runs sensors on the business rule set pays for each sensor, and the personal plan does not cover company use.
Hosting is the next line. A self-run service on a DigitalOcean Droplet with 4 GiB of RAM and 2 vCPUs costs $24 a month, or $288 a year, before anyone configures it.
Staff time is the line no vendor prices, so this guide does not put a dollar figure on it. Budget it as its own line, with a named owner for each tool.
Key features to look for
Pricing
How we ranked: we read each project's license file and each paid plan on its own page on 10 October 2026. We ranked the ten tools by three tests: the license terms a company must accept, how much of the job the free version covers without a paid add-on, and the bill that appears after install.
We did not test the tools ourselves. Where a vendor publishes no price, the page says so and never estimates one.
Snort's product page lists the Business rule set per sensor for a one-year subscription and the Personal set at $29.99, for home networks or education only.
Semgrep's pricing page lists the free edition at $0 for up to 10 contributors and prices Teams per contributor per month.
DigitalOcean's Droplet pricing lists a 4 GiB, 2 vCPU plan at $24 a month.
The scenario has 25 staff, 12 developers committing to private repositories, two Snort sensors on Business rules and one self-run service.
Snort costs 2 x $399 = $798 a year. Semgrep costs 12 x $30 = $360 a month, or $4,320 over twelve months at the monthly rate, since the page shows no annual price. The Droplet costs $24 x 12 = $288 a year. The total is $798 + $4,320 + $288 = $5,406 a year, before staff time, hardware and any support contract.
A team with 10 or fewer contributors pays nothing for Semgrep's Code and Supply Chain scanning on the free edition.
| Plan | Price | Best for |
|---|---|---|
| OPNsense community edition | Free | Simplified 2-clause BSD/MIT license; the firewall platform itself has no license fee |
| OPNsense Business Edition | Not published | Adds a web application firewall, proxy access and an extended blocklist; no price on the site |
| Suricata engine | Free | GPL-2.0 engine; the commercial ET PRO rules are a separate subscription with no price shown |
| Zeek | Free | BSD license; the repository lists no paid plan or support price |
| Snort 3 Personal rules | $29.99 a year | One-year subscription for home networks or education only; rules 30 days ahead of registered users |
| Snort 3 Business rules | $399 per sensor a year | One-year subscription for business, nonprofit, education and government use in production |
| Semgrep Free Edition | Free | Up to 10 contributors and 10 repositories; Code and Supply Chain included, Secrets not included |
| Semgrep Teams | From $30 per contributor a month | Code and Supply Chain scanning; Secrets adds $15 per contributor a month |
| Falco | Free | Apache 2.0, CNCF graduated; Sysdig Secure uses Falco rules and is sold separately |
| Trivy | Free | Apache-2.0; Aqua builds a product on Trivy and shows no price in the repository |
| Keycloak | Free | Apache-2.0; no support plan or price in the repository |
| OpenBao | Free | MPL-2.0 fork of Vault; the project lists no price |
| Velociraptor | Free | AGPL-3.0; no paid plan or support price listed in the repository |
| DigitalOcean 4 GiB, 2 vCPU Droplet | $24 a month | Example host for one self-run service; $0.03571 an hour |
The bottom line
For a 25-person company, the open licenses are real, and the bill comes from rules, contributor caps and hosting. In our scenario the stack costs $5,406 a year before staff time, and Semgrep's paid tier is the largest line.
OPNsense, Zeek and Suricata cost nothing to license, and Falco, Trivy and Keycloak are also free to license for container, build and login work. Read the license before rollout: Vault 1.15.0 and later is not open source, and OpenBao is the open-source fork under MPL-2.0.
For the free scanners and SIEM tiers this list leaves out, start with our free vulnerability scanners guide and free SIEM guide.
Cite this: Cyberpresso, "Best Open-Source Security Tools in 2026: What Is Free and What It Costs to Run", vendor prices checked 10 October 2026.
Frequently asked questions
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