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Drools

kie.apache.org

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Spec score 8.0 #6 of 18 in Business Rules Management Software

What it is

Drools is a free, open-source rule engine for building expert systems with forward- and backward-chaining inference. Its DMN engine supports Conformance level 3, covering the features in that standard, and can statically analyze decision tables for gaps and overlaps. For event processing, it reasons over streams using temporal operators, sliding windows, and event expiration. Developers can define rules in DRL text files alongside Java code, or use Excel decision tables, rule templates, or a Java executable model API. Rule units organize rules with typed containers for input data, and Kogito can generate REST endpoints from them. Drools rules can also be called by a BPMN business rule task in jBPM within the same service. Apache KIE states that the DMN engine passes 99.9% of DMN TCK tests as of version 10.2.0. The project is available for API, Linux, and self-hosted use at free. Getting started requires an IDE, JDK 21 or 17, and Maven 3.9 or later. Apache KIE is undergoing incubation and has not yet been fully endorsed by the ASF.

Spec sheet

Purpose
Drools is a forward-chaining and backward-chaining inference-based rule engine used to build expert systems.Read 5 Oct 2026 · kie.apache.org
Integrations
Drools rules can be called directly by a BPMN business rule task in jBPM within the same service.Read 5 Oct 2026 · kie.apache.org
Security
The Apache Security Team coordinates handling of Apache project vulnerabilities and encourages private reports before public disclosure.Read 5 Oct 2026 · apache.org
Support
The project lists a users mailing list and Zulip chat as community contact channels.Read 5 Oct 2026 · kie.apache.org
Founded
2001Read 28 Sep 2026 · kie.apache.org
Decision modeling
Its DMN engine provides runtime support at Conformance level 3, covering every feature in the standard.Read 5 Oct 2026 · kie.apache.org
Developer prerequisites
The getting started guide lists an IDE, JDK 21 or 17, and Maven 3.9 or later as prerequisites.Read 5 Oct 2026 · kie.apache.org
DMN test results
The project states that as of Apache KIE 10.2.0, its DMN engine passes 99.9% of the DMN TCK tests.Read 5 Oct 2026 · kie.apache.org
DMN validation
The DMN engine statically analyzes decision tables to detect gaps and overlaps and check that table rules follow industry best practices.Read 5 Oct 2026 · kie.apache.org
Event processing
Its Complex Event Processing engine reasons over event streams using temporal operators, sliding windows, and event expiration.Read 5 Oct 2026 · kie.apache.org
Project status
Apache KIE is undergoing incubation, and the site says incubation means it has yet to be fully endorsed by the ASF.Read 5 Oct 2026 · kie.apache.org
Rule authoring
Rules can also be expressed through Excel decision tables, rule templates, or a Java executable model API.Read 5 Oct 2026 · kie.apache.org
Rule language
DRL lets developers define rules in plain text files alongside Java code and under version control.Read 5 Oct 2026 · kie.apache.org
Rule units
Rule units organize rules with typed containers for their input data, and Kogito can generate REST endpoints from them.Read 5 Oct 2026 · kie.apache.org

Plans and prices

Apache Drools (free) Free Apache software download and use at no cost · Java based Read 5 Oct 2026 · apache.org

Every Drools plan and price →

Strong points and limits

Strong points

  • Supports full DMN standard at Conformance level 3
  • Offers several rule-authoring methods
  • Includes event-stream processing capabilities
  • Free Apache software at free

Limits

  • Getting started requires an IDE and JDK
  • Requires Maven 3.9 or later
  • Apache KIE is still undergoing incubation

Who it suits

Drools suits developers building expert systems or working with decision models and event streams. The listed prerequisites include an IDE, JDK 21 or 17, and Maven 3.9 or later.

Verdict

Drools offers multiple ways to author rules and supports DMN and complex event processing. It is free to use, with specific development prerequisites and Apache KIE incubation status to consider.

Where Specifiction places it

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