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Articles, updated 8 min read

Free SIEM Tools in 2026: 8 Options and What They Really Cost

By UTMStack Team

“Free SIEM” covers three very different things: open source software you can run forever at no license cost, free editions of commercial products with a cap on how much you can do, and free trials that end. All three show up in the same search results, and picking the wrong kind is how teams end up rebuilding their security monitoring a year later.

This guide sorts the free options people actually use, says plainly what each one leaves out, and explains what a free SIEM still costs to run. We build UTMStack, one of the options, so weigh our view accordingly.

The short answer: the best free SIEMs are open source and have no time limit: UTMStack Community for a complete SIEM with response and compliance reports, Wazuh for endpoint monitoring, Security Onion for network monitoring, and OpenSearch or Elastic’s free tier if you want to build your own. Free tiers of commercial SIEMs, such as Splunk Free, are capped (500 MB of logs a day and no alerting). The software costs nothing; servers, setup and the time to watch alerts still do.

Three kinds of free

How long it stays free, and what the catch is

Free foreverOpen source and free editionsUTMStack Community, Wazuh, OpenSearch, Security Onion, Graylog Open, Elastic Basic. You run it; you pay for servers and time.
Free with a capFree tiers of commercial SIEMsFor example, Splunk Free: 500 MB of logs a day, no alerting, one user.
Free for a whileFree trialsFor example, Microsoft Sentinel's first 10 GB a day for 31 days. Good for testing, not for a program that runs for years.

The free SIEM options

1. UTMStack Community

A complete SIEM in one install, free under the AGPL-3.0 open source license. It collects logs from Windows and Linux agents, syslog and cloud accounts, checks every event against 600+ detection rules mapped to MITRE ATT&CK as it arrives, and turns related events into alerts and incidents. Response flows can block an address, disable an account or isolate a host through the agent, and it produces CMMC 2.0 and GDPR compliance reports from your own logs. UTMStack is listed in CISA’s catalog of free cybersecurity services and tools.

  • Limits of the free edition: the SOC-AI assistant, the other seven compliance frameworks (including PCI DSS, HIPAA, ISO 27001 and SOC 2), single sign-on, multi-tenancy, the macOS agent and 24/7 support are in the paid Enterprise edition. Help comes from the community on GitHub.
  • Runs on: one Ubuntu 24.04 or Red Hat compatible server; 4 cores, 16 GB of memory and 150 GB of disk cover about 50 data sources.
  • Best for: teams that want detection, response and audit evidence without assembling separate tools.

2. Wazuh

Free under GPLv2. Its agent does file integrity monitoring, configuration checks and vulnerability detection on almost any operating system, and the server correlates events into alerts.

  • Limits: playbooks and case management need extra tools such as Shuffle; separating customers for a managed service is your own design work.
  • Runs on: 4 vCPUs and 8 GB of memory for up to 25 agents, per its quickstart.
  • Best for: endpoint-focused monitoring on modest hardware. See our Wazuh alternatives guide for how it compares.

3. Security Onion

A free Linux distribution for network security monitoring, with Suricata, Zeek, packet capture and an analyst console.

  • Limits: the Elastic License 2.0 forbids offering it to others as a hosted or managed service, and a standalone install needs 24 GB of memory or more.
  • Best for: in-house teams hunting on network traffic.

4. Elastic Security (free Basic tier)

On self-managed deployments, Elastic’s free Basic tier includes the detection engine, Elastic’s prebuilt detection rules, the investigation timeline and case management.

  • Limits: machine learning, entity risk scoring and some connectors need a paid subscription; you design, size and maintain the cluster yourself.
  • Best for: teams with engineers who want a search-first platform.

5. OpenSearch Security Analytics

Apache 2.0 throughout, with Sigma detection rules and a correlation engine.

  • Limits: it is a search platform with a security layer; collection, response and reporting are yours to build.
  • Best for: teams already running OpenSearch.

6. Graylog Open

Free log collection, parsing, search, dashboards and alerting with no ingestion cap, under the SSPL.

  • Limits: correlation rules, Sigma rules and anomaly detection are in the paid Graylog Security product.
  • Best for: log management first, security second.

7. Splunk Free

The free license of Splunk Enterprise. It never expires and indexes up to 500 MB of data a day.

  • Limits: no alerting, no user accounts, and search is disabled if you exceed the daily limit more than three times in 30 days. Without alerting it is a search tool rather than a working SIEM.
  • Best for: learning Splunk’s search language.

8. Microsoft Sentinel free trial and free data sources

Sentinel is billed by the gigabyte, but new workspaces get their first 10 GB a day free for 31 days, and some data, such as Azure activity logs and Office 365 audit logs, can be ingested at no charge.

  • Limits: after the trial, everything else is billed by volume, so it is a paid SIEM with a free start.
  • Best for: organizations already deep in Microsoft’s cloud that want to test before buying.

At a glance

OptionKind of freeAlertingAutomated responseCompliance reportsMain limit
UTMStack CommunityOpen source (AGPL-3.0)YesBuilt inCMMC 2.0, GDPRSeven more frameworks, SSO and multi-tenancy are paid
WazuhOpen source (GPLv2)YesActive response scriptsFramework mappingsCases and playbooks need extra tools
Security OnionSource-availableYesLimitedNoHeavy hardware; no managed service use
Elastic BasicFree tierYesLimitedNoSome features paid; you build the stack
OpenSearchOpen source (Apache 2.0)YesNoNoCollection and response are yours to build
Graylog OpenSource-availableBasicNoNoCorrelation and Sigma rules are paid
Splunk FreeCapped free tierNoNoNo500 MB a day, one user
Sentinel trialFree for 31 daysYesYesThrough add-onsBilled by volume after the trial

What a free SIEM still costs

The license is the only part that is free. Plan for the rest before you start:

What you still pay for with a free SIEM

The costs that remain when the license is free

  1. A serverFor UTMStack, 4 cores, 16 GB and 150 GB of SSD cover about 50 sources
  2. SetupInstall, connect sources, turn on the right logging: a few days
  3. TuningThe first weeks of cutting false alarms
  4. Someone watchingA few hours a week for a small company, more as you grow
Automated response lowers the last cost: blocking a brute-force source or disabling a compromised account does not need a person awake at 3 a.m.

For the full picture of paid options, see how much a SIEM costs. To size the server, use the SIEM sizing calculator.

When free stops being enough

A free SIEM is a good fit as long as someone on your team can install, update and tune it. These are the usual signs you have outgrown it:

  • An auditor needs a framework the free edition does not cover, such as PCI DSS or HIPAA reports.
  • Nobody can watch alerts at night, and you need support or analysts behind you.
  • You serve several customers or business units and need their data kept apart.
  • You want single sign-on, custom roles or an AI assistant for your analysts.

With UTMStack, moving up does not mean starting over: the Enterprise edition runs on the same servers, and UTMStack Cloud runs the same platform as a dedicated hosted instance. Both are priced per device, never by log volume.

How to start for free

  1. Click through the live demo with sample data to see whether the workflow suits you. No sign-up is needed.
  2. Install the free edition on a spare server or virtual machine; the installer takes 15 to 30 minutes.
  3. Connect three sources first: a domain controller or main server, your firewall, and Microsoft 365 or another cloud account. They catch the most common attacks.

For a deeper comparison of the open source options, read the best open source SIEM tools. Small businesses should also read SIEM for small business.

Frequently asked questions

Is there a completely free SIEM? Yes. UTMStack Community, Wazuh and OpenSearch are open source with no time limit or log cap; Security Onion, Graylog Open and Elastic’s Basic tier are free to run but source-available. You still pay for the servers and the time to run them.

What is the best free SIEM for a small business? One that works without a team of engineers. UTMStack Community puts detection, automated response, incidents and compliance reports in one install. Wazuh is lighter if endpoint monitoring is what you need most.

Is Splunk free? Splunk Free is a free license of Splunk Enterprise that indexes up to 500 MB a day, with no alerting and no user accounts. It suits learning, not monitoring a business.

Is Wazuh free? Yes, under GPLv2, including for commercial use.

What is the difference between a free SIEM and an open source SIEM? Open source means you may run, change and redistribute the code under its license. Free can also mean a capped free tier or a trial of a commercial product, which can change or end.

Can a free SIEM meet compliance requirements? It can collect, protect and keep the logs that frameworks require. UTMStack’s free edition also produces CMMC 2.0 and GDPR reports; other frameworks need its Enterprise edition, and most free tools leave reporting to you.

Sources

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