Suricata is an open-source IDS, IPS and network security monitoring engine from the Open Information Security Foundation. Zeek is an open-source passive network traffic analyser, best known as a network security monitor that turns packets into high-fidelity transaction logs and a scripting platform. Both are free to run. Both are staples of blue-team pipelines. They solve overlapping problems in very different ways. We read the project sites, the manuals, the licences and the current release notes. Checked on 28 October 2026.
Documentation review: not tested. We have not used the products in this review. It is a structured reading of published evidence, linked throughout. How we review products explains what that covers.
Status: correct as at 28 October 2026. Both projects are free under open-source licences; there is no commercial list price for the engines themselves.
Disclosure: no vendor sponsored, reviewed or saw this review before publication, and there are no affiliate links. Our independence policy explains how we work.
Verdict
Pick Suricata when you need signature detection and the option of inline blocking; pick Zeek when you need protocol-aware transaction logs and a scripting language for investigations. Most mature NSM stacks run both.
- Good for: Suricata suits teams that want multi-threaded IDS/IPS with Emerging Threats-style rule feeds and structured EVE JSON alerts. Zeek suits teams that want conn/dns/http/ssl-style transaction data, file extraction and custom detection written as scripts rather than signatures.
- Not for: Suricata is a poor sole choice if your primary need is rich, judgement-free protocol history rather than alerts. Zeek is a poor sole choice if you need classic signature IDS or inline packet drop; its own docs point signature work at Suricata or Snort.
- Price: Both engines are free. Suricata is licensed under GPL-2.0 (opens in a new tab). Zeek ships under a BSD-style LBNL/ICSI licence (opens in a new tab). Hardware, SPAN/TAP, and optional commercial rule feeds are separate costs.
- Score: No numeric score (documentation review)
What each project is
Suricata’s own documentation (opens in a new tab) describes it as a high-performance Network IDS, IPS and Network Security Monitoring engine developed by the Open Information Security Foundation (OISF). It is multi-threaded, supports hardware acceleration options documented by the project, and can run in IDS (passive) or IPS (inline) modes. Output is built around the Extensible Event Format (EVE) JSON channel for alerts, flows, HTTP, DNS, TLS and file metadata, among other event types.
Zeek’s documentation (opens in a new tab) describes it as a passive, open-source network traffic analyser. Operators commonly use it as a network security monitor: by default it emits a compact, richly annotated set of transaction logs covering every connection and many application-layer protocols (HTTP with URIs and headers, DNS, SSL/TLS certificates, SMTP and more). Detection beyond logging is expressed in Zeek’s domain-specific scripting language. The same docs state plainly that Zeek is not a classic signature-based IDS, and that users seeking that model are better served by Suricata or Snort. They also state that Zeek does not participate in the kernel’s packet-forwarding decisions, which rules out inline IPS as a design goal.
Versions and licences (28 October 2026)
Suricata’s current stable release is 8.0.7 (opens in a new tab), published 15 September 2026; the download page also lists 7.0.17 as the last 7.x line, marked end of life on 7 July 2026. The engine is licensed under the GNU General Public License version 2 (COPYING (opens in a new tab) on the OISF/suricata repository).
Zeek’s Get Zeek (opens in a new tab) page lists current release 9.0.1 and previous LTS 8.0.11, both dated 26 October 2026. The project began as Bro at Lawrence Berkeley National Laboratory in the mid-1990s and was later renamed; the history is documented in the Book of Zeek (opens in a new tab). The source tree carries a BSD-style licence from LBNL and ICSI (COPYING (opens in a new tab)).
Head-to-head
| Dimension | Suricata | Zeek |
|---|---|---|
| Primary role | IDS, IPS and NSM engine | Passive NSM and traffic analysis platform |
| Inline blocking | Yes (IPS/inline documented for Netfilter, AF_PACKET, DPDK) | No (passive; no packet-forwarding role) |
| Detection model | Signature/rules-first (plus app-layer parsers) | Scripting-first; notices; not signature-centric |
| Default output | EVE JSON (alerts, flows, HTTP, DNS, TLS, files…) | Tab-separated or JSON protocol logs (conn, dns, http, ssl…) |
| Threading / scale | Multi-threaded engine; runmodes in suricata.yaml | Clusters with front-end load balancing across workers |
| Rule / intel feeds | Emerging Threats open/Pro and other rulesets named by the project | Intel framework and packages; not ET-style IDS rules |
| Licence | GPL-2.0 | BSD-style (LBNL/ICSI) |
| Stable / current (checked 28 Oct 2026) | 8.0.7 (15 Sep 2026) | 9.0.1 and LTS 8.0.11 (26 Oct 2026) |
| GitHub stars (28 Oct 2026) | 6,785 (OISF/suricata) | 8,146 (zeek/zeek) |
| Gartner Peer Insights | Not verified for this review | Not verified for this review |
GitHub star counts are a crude activity signal, not a quality score. We include them only because they are public, dated and reproducible from the repository APIs on the day of the check. They do not replace peer reviews.
Suricata: signatures, EVE and the IPS option
If your mental model of network defence still starts with “match this pattern, raise that alert”, Suricata is the straight answer. The features page (opens in a new tab) lists IDS, IPS and NSM in one engine, multi-threading, HTTP/SSL/TLS/DNS protocol parsers, file extraction and identification, and EVE JSON as the modern logging path. Rule management is a first-class concern: the project documents how to load and update rules, and names Emerging Threats and VRT-style sources among the rulesets people actually run.
Proofpoint still publishes the Emerging Threats open rules (opens in a new tab); the open/ tree on that index was updated on 27 October 2026 when we checked. That matters for teams who want a free signature baseline without inventing every rule themselves. Commercial ET Pro and other paid feeds exist; we did not price them here because this review covers the engines, not a particular feed contract.
The IPS story is real, not marketing gloss. Suricata 8.0 documentation includes a dedicated Setting up IPS/inline for Linux (opens in a new tab) chapter covering Netfilter/NFQUEUE, Layer-2 AF_PACKET IPS and DPDK IPS. That is the operational difference that makes Suricata a firewall peer rather than a pure sensor. Inline mode is also where you get to discover that your SPAN port was the wrong tool for the job — but that is an architecture problem, not a Suricata problem.
EVE JSON is the other practical reason shops stick with Suricata. Alerts, flows and protocol events land in one schema that SIEM and data-lake pipelines already know how to ingest. You still have to tune rules and manage false positives; the engine will not do that for you. Documentation reviews never prove how noisy a default ruleset is on your network, and we will not pretend otherwise.
Zeek: logs, scripts and clusters
Zeek starts from a different question: what actually happened on the wire, recorded as structured transactions rather than as judgements. The Why Zeek? (opens in a new tab) page places it in the network security monitoring tradition — transaction data, extracted content and some alert/notice capability — and is candid that full-content capture and classic signature IDS are better handled by other tools. Suricata is named explicitly in that comparison.
Out of the box you get the familiar log set: conn.log (opens in a new tab) for every connection, plus dns, http, ssl, files and a long list of protocol-specific logs documented in the Book of Zeek. Logs can be tab-separated or JSON. That feed is gold for threat hunting, incident response timelines and “show me every DNS query for this domain last Tuesday” work. It is less useful if all you wanted was a red banner that says DROP.
Custom detection lives in Zeek’s scripting language — described in the docs as a domain-specific, Turing-complete language with a large standard library. That is power and a learning curve in the same package. Teams that already think in “write a small programme against protocol events” tend to love it; teams that only want to toggle signature IDs tend to bounce. Clustering is a first-class scale path: a front-end load balancer can slice traffic across workers, coordinated by a manager, as described in the what-is and cluster documentation.
Together, not instead
The cleanest reading of both projects’ own documentation is that they are complements. Our free threat hunting toolkit for small teams already names both engines in the wider stack; this piece is the head-to-head on the engines themselves. Suricata covers signature detection and optional inline response; Zeek covers deep protocol logging and scriptable analysis. Plenty of open-source NSM distributions ship both for that reason. Choosing only one is fine when your use case is narrow — a small shop that only needs ET-style alerts, or a research network that only needs Zeek logs — but the published design intent of each project points at coexistence more often than at a cage match.
Licence posture differs in a way that can matter to product teams. Suricata’s GPL-2.0 copyleft is straightforward for internal SOC use and more careful if you are shipping a proprietary appliance around a modified engine. Zeek’s BSD-style licence is generally more permissive for redistribution; read the COPYING file and take counsel for your own case rather than treating this paragraph as legal advice.
Where they sit in the stack
Neither tool is a SIEM, an EDR or a full packet-capture archive. Suricata and Zeek sit on a tap, SPAN or inline path and emit events and logs for something else to store and query. In practice that “something else” is often Elasticsearch, OpenSearch, Splunk, or a data lake; open-source NSM distributions such as Security Onion historically wire both engines into that pipeline. We already covered Security Onion in a separate SIEM piece for small teams, so this review stays on the two engines alone. For endpoint hunts beside the network sensors, see our Velociraptor DFIR review.
Operational cost is mostly people and packets, not licences. You still need reliable traffic visibility, disk for logs, and someone who understands either rule tuning or Zeek scripting. The free licence removes the purchase order; it does not remove the on-call rota.
What we could not verify
- Gartner Peer Insights (or equivalent) product scores for Suricata or Zeek as standalone network products. We found no public, citeable score page we could confirm on 28 October 2026 without inventing figures, so the table marks both as not verified.
- Throughput claims on specific hardware. Project marketing and community posts quote multi-gigabit figures under lab conditions; we did not reproduce them and do not repeat unverified numbers here.
- Commercial Emerging Threats Pro or other paid rule-feed list prices on the day of review.
- Hands-on false-positive rates, CPU cost or operator workload on any live network.
Who should pick which
Choose Suricata if you need an open-source IDS that can also sit inline, you already operate (or plan to operate) Emerging Threats-style rules, and your SIEM expects EVE JSON alerts and flow records. It is the closer spiritual successor to the classic Snort workflow, with multi-threading and modern protocol parsers built in.
Choose Zeek if your priority is durable network truth — connection and application logs you can query months later — and you have (or can grow) staff who will write and maintain Zeek scripts. Use it when “what did this host talk to?” matters more than “which signature ID fired?”.
Run both if you are building a serious NSM capability and can afford the sensor footprint. That is what the projects themselves imply when Zeek’s docs defer signature IDS to Suricata, and when Suricata’s NSM features stop short of Zeek’s scripting depth.
Neither project replaces endpoint telemetry, cloud audit logs or a human who can read a timeline. They are network sensors with very different personalities. Pick the personality that matches the question you ask most often — or, if staff time and rack space allow, refuse the false choice and keep both.
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