head to head · open source
opa vs ossec-hids
opa has 12,425 GitHub stars, 1,706 forks, 310 open issues and last shipped yesterday. ossec-hids has 5,070 stars, 1,074 forks, 125 open issues and last shipped 2 days ago. opa leads on adoption by 145% (12,425 vs 5,070 stars). opa is written in Go under Apache-2.0; ossec-hids is written in C under GPL-2.0. opa has attracted 14% as many forks as stars, ossec-hids 21%. opa was the more recently maintained of the two, and both are self-hostable with no licence fee. The two share 1 topic tag (compliance), so they are genuine substitutes rather than adjacent tools.
Two open source projects, one decision. Both are free and self-hostable — the differences are community size, license terms, language stack and release pace.
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Side by side
| opa | ossec-hids | |
|---|---|---|
| GitHub stars | ★ 12K | ★ 5.1K |
| License | Apache-2.0 | GPL-2.0 |
| Written in | Go | C |
| Last push | 2026-11-04 | 2026-11-03 |
| Forks | ⑂ 1.7K | ⑂ 1.1K |
| Self-hosting | Yes | Yes |
| Data ownership | Your server | Your server |
pick opa if
- You weight community size — 12K stars and counting
- You want the Apache-2.0 license terms
- Your stack matches Go
- You value the larger contributor base for long-term maintenance
pick ossec-hids if
- You want the ossec-hids feature set and don't need the biggest community
- You prefer the GPL-2.0 license terms
- Your stack matches C
- You evaluated both and ossec-hids fits your workflow better
About opa
Open Policy Agent Open Policy Agent (OPA) is an open source, general purpose policy engine that enables unified, context aware policy enforcement across the entire stack. OPA is proud to be a graduated project in the Cloud Native Computing Foundation (CNCF) landscape. For details read the CNCF announcement. Get started with OPA Write your first Rego policy with the Rego Playground or use it to share your work with others for feedback and support. Have a look at the Access Control examples if you're not sure where to start. Install the VS Code extension to get started locally with live diagnostics, debugging and…
About ossec-hids
OSSEC v4.3.0 Information about OSSEC OSSEC is a full platform to monitor and control your systems. It mixes together all the aspects of HIDS (host based intrusion detection), log monitoring and SIM/SIEM together in a simple, powerful and open source solution. Visit our website for the latest information. www.ossec.net Current Releases The current stable releases are available on the ossec website. Releases can be downloaded from: Downloads Release documentation is available at: docs Development The development version is hosted on GitHub and just a simple git clone away. Screenshots File Integrity Monitoring…
read the full ossec-hids overview →
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Frequently asked questions
Is opa or ossec-hids more popular?
opa has 12,425 GitHub stars and ossec-hids has 5,070. opa has the larger community by that measure.
Are opa and ossec-hids free?
Both are open source. opa is licensed under Apache-2.0 and ossec-hids under GPL-2.0. Neither carries a licence fee.
What is the difference between opa and ossec-hids?
opa is written in Go and ossec-hids in C. The practical differences are community size, licence terms, language stack and release cadence — all compared in the table above.
Which should I choose, opa or ossec-hids?
Choose opa if you want the larger community (12,425 stars) or its Apache-2.0 licence terms. Choose ossec-hids if its feature set, stack or GPL-2.0 licence fits better. Both are self-hostable.