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 every feature in the standard, and statically checks decision tables for gaps, overlaps, and rule practices. The project says that as of Apache KIE 10.2.0, the engine passes 99.9% of DMN TCK tests. For event processing, Drools reasons over streams using temporal operators, sliding windows, and event expiration. Developers can define rules in DRL text files alongside Java code and version them, or use Excel decision tables, rule templates, and a Java executable model API. Rule units group rules with typed input-data containers; 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. The getting-started guide lists an IDE, JDK 21 or 17, and Maven 3.9 or later as prerequisites. Apache KIE is in incubation and is not yet fully endorsed by the ASF. Community contact options include a users mailing list and Zulip chat.
Who it is for
Drools suits developers building expert systems, decision models, or event-processing applications. Its guide lists an IDE, JDK 21 or 17, and Maven 3.9 or later as prerequisites.
What is good
- DMN engine covers all features at Conformance level 3
- Supports stream processing with temporal operators and sliding windows
- Rules can be authored in several formats
- Free Apache software
What to know first
- Requires an IDE, JDK 21 or 17, and Maven 3.9 or later
- Apache KIE is still in incubation
Verdict
Drools provides multiple rule-authoring paths alongside DMN and event-processing capabilities. Developers should account for the listed prerequisites and Apache KIE’s incubation status.
Drools plans and pricing
All plansCompared on business rules management software
- Decision tables
- Yes
- Visual rule authoring
- Yes
- Rule testing tools
- Yes
- DMN support
- Yes
- Natural-language rules
- Yes
- Execution access
- both
