Are There any Open Source Rules Engine?

Compare the top open-source rules engines for your business needs. Learn about their features, benefits, and pricing to choose the best one for you.

Prabhat Gupta

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Are There any Open Source Rules Engine?
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In the ever-evolving landscape of software development and business rule automation, open-source rules engines are becoming increasingly important. These engines serve as the backbone for decision-making processes, enabling businesses and developers to define, manage, and execute complex rules efficiently.

In this blog, we will explore the world of open-source rules engines, their applications, and how they can streamline decision-making in various domains. We will delve into a variety of open-source rules engines, from those compatible with popular programming languages to specialized solutions. By the end of this blog, you will have a comprehensive understanding of the open-source rules engine landscape and be able to make informed decisions about which one might best suit your needs.

So, let's embark on this journey into the world of open-source rules engines and discover the power they bring to the table in automating decision-making processes, enhancing software development, and driving business efficiency.

What is a Rule Engine?

A rule engine is a specialized software system designed to manage and execute business rules efficiently. Business rules are conditional statements or logical expressions that define the behavior, decisions, and policies of an organization. Rule engines play a crucial role in automating decision-making processes, ensuring consistency, and enabling dynamic responses to changing conditions.

Core Components of a Rule Engine:

To understand rule engines better, let's explore their core components:

  1. Rule Repository: This is where business rules are stored, managed, and organized. Rules are typically defined in a human-readable format, making them accessible to non-technical stakeholders.
  2. Rule Authoring Interface: Rule engines often provide user-friendly interfaces for business analysts and domain experts to define, modify, and test rules without the need for coding skills. These interfaces may include graphical rule editors, decision tables, or domain-specific languages (DSLs).
  3. Rule Execution Engine: The heart of the rule engine is its execution engine. It interprets and evaluates rules based on input data and executes actions associated with rules that are evaluated to be true. This process is often referred to as rule inference.
  4. Rule Evaluation: Rule engines evaluate rules by matching input data against conditions specified in the rules. If a rule's conditions are met, it is considered true, and associated actions are executed. Multiple rules can be evaluated sequentially or concurrently.
  5. Action Execution: When a rule evaluates to true, the rule engine triggers predefined actions. These actions can include updating databases, sending notifications, generating reports, or making decisions that affect a business process.

In summary, a rule engine is a critical tool for organizations looking to automate decision-making processes, ensure consistency in rule execution, and respond dynamically to changing conditions. It simplifies rule management, allows for non-technical rule authoring, and finds applications across a wide range of industries.

Are There any Open Source Rules Engine?

Yes, there are several open-source rules engines available that empower developers and businesses to implement rule-based decision-making processes efficiently.

Open-source rules engines abound in the software development and business automation landscape, providing flexible, cost-effective, and collaborative solutions for managing and executing rules. In the sections that follow, we will explore these open-source rules engines, shining a spotlight on some of the notable options available.

But first let’s see some popular open-source language-based rule engines:

Node.js Rule Engines

Node.js has gained immense popularity as a runtime environment for building server-side applications using JavaScript. When it comes to rule engines in the Node.js ecosystem, there are a few noteworthy options:

1. Nools (Node.js Rules Engine): Nools is a powerful, production-ready Node.js rule engine. It's designed to be easy to use and highly efficient. With Nools, you can define rules using a simple JavaScript-like syntax, making it accessible for developers familiar with the language. It's particularly suitable for scenarios where real-time rule evaluation and execution are required.

// Import the Nools package
const nools = require('nools');

// Define a simple rule file in a string
const ruleFile = `
rule "Example Rule" {
    when {
        m : Message m.text == "hello";
    then {
        console.log("Nools: Hello detected!");

// Create a new flow from the rule
const flow = nools.compile(ruleFile, { name: "example" });
const Message = flow.getDefined("message");
const session = flow.getSession(new Message("hello"));

// Fire the rules
    function () {
        console.log("Nools: Rule execution completed.");
    function (err) {

// Define a simple message class
function Message(text) {
    this.text = text;

2. json-rules-engine: As the name suggests, json-rules-engine allows you to define rules using JSON, which can be advantageous for scenarios where rule configurations need to be dynamic or manageable externally. It provides a straightforward way to create and execute rules within a Node.js application.

// Import the json-rules-engine package
const { Engine } = require('json-rules-engine');

// Create a new rules engine
const engine = new Engine();

// Define a rule
const rule = {
    conditions: {
        all: [{
            fact: 'message',
            operator: 'equal',
            value: 'hello'
    event: {
        type: 'messageDetected',
        params: {
            message: 'json-rules-engine: Hello detected!'

// Add the rule to the engine

// Define a fact
const facts = { message: 'hello' };

// Run the engine with the defined facts
    .then(results => { => console.log(event.params.message));

These Node.js rule engines offer flexibility and efficiency for businesses and developers looking to implement rule-based systems within their JavaScript-based applications. Depending on your specific use case and requirements, you can choose the one that aligns best with your project.

Java Rule Engines

Java is renowned for its versatility and robustness in building enterprise-level applications. When it comes to rule engines in the Java ecosystem, several options cater to diverse needs.

Here’s an example of a simple rule application where rules are evaluated based on given data:

import java.util.*;

// Assuming a simple rule interface for demonstration
interface Rule {
    boolean evaluate(Map data);
    void execute();

// An example rule implementation
class ExampleRule implements Rule {
    public boolean evaluate(Map data) {
        // Example condition: Check if the data contains a specific value
        return "hello".equals(data.get("message"));

    public void execute() {
        System.out.println("Rule triggered: Message is hello");

// Main class to demonstrate rule engine logic
public class RuleEngineDemo {
    private List rules;

    public RuleEngineDemo() {
        rules = new ArrayList<>();
        // Add rules to the engine
        rules.add(new ExampleRule());

    public void runRules(Map data) {
        for (Rule rule : rules) {
            if (rule.evaluate(data)) {

    public static void main(String[] args) {
        RuleEngineDemo engine = new RuleEngineDemo();

        // Create a data map for rule evaluation
        Map data = new HashMap<>();
        data.put("message", "hello");

        // Run the rule engine with the data

Here are a couple of notable Java rule engines:

  1. Drools: Drools is perhaps the most well-known open-source business rule management system in the Java community. It provides a comprehensive set of tools for authoring, storing, managing, and executing business rules. Drools is highly extensible and offers features like decision tables, a rule language, and a powerful inference engine. It's widely used in industries where complex decision-making processes are a common occurrence, such as finance and healthcare.
  2. Easy Rules: Easy Rules is a lightweight rule engine for Java applications. It follows a simple and intuitive design, making it an excellent choice for scenarios where you need a straightforward rule engine without the complexity of more extensive systems like Drools. Easy Rules focuses on simplicity and ease of integration into Java applications.

These Java-based rule engines are ideal for businesses and developers working within the Java ecosystem. Whether you need an advanced business rule management system like Drools or a lightweight solution like Easy Rules, Java rule engines offer a wide spectrum of options to address your specific rule-based requirements.

Read Also: Rule Engine for Healthcare: Transforming Medical Decision-Making

C# Rule Engines

For developers working in the Microsoft technology stack, C# rule engines are essential for building rule-based systems and applications. These rule engines seamlessly integrate with the C# programming language, making it easier to implement and manage business rules. Here are a couple of noteworthy C# rule engines:

  1. NRules: NRules is a powerful open-source rules engine for .NET that enables developers to create complex rule-based applications in C#. It is designed to be highly expressive and efficient, allowing you to define rules using plain, idiomatic C# code. NRules supports forward-chaining and backward-chaining inference strategies, making it suitable for a wide range of applications, from simple rule evaluation to complex decision rule automation( i.e. decision engine).
  2. Windows Workflow Foundation (WF): Although not strictly a rule engine, Windows Workflow Foundation provides a framework for building workflow-driven applications in C#. It allows you to define rules and logic as part of the workflow, enabling dynamic decision-making and process automation. WF is particularly useful when you need to integrate rule-based workflows into your applications.

Here's a basic structure of rules in C#:

using System;
using System.Collections.Generic;

// Define a rule interface
public interface IRule
    bool ShouldRun(Dictionary data);
    void Execute();

// An example rule implementation
public class ExampleRule : IRule
    public bool ShouldRun(Dictionary data)
        return data.ContainsKey("message") && data["message"].Equals("hello");

    public void Execute()
        Console.WriteLine("Rule executed: Message is hello");

// Rule engine class
public class RuleEngine
    private List _rules = new List();

    public RuleEngine()
        _rules.Add(new ExampleRule());

    public void Run(Dictionary data)
        foreach (var rule in _rules)
            if (rule.ShouldRun(data))

    public static void Main(string[] args)
        RuleEngine engine = new RuleEngine();

        var data = new Dictionary { { "message", "hello" } };

C# rule engines like NRules and the workflow capabilities of Windows Workflow Foundation empower C# developers to implement rule-driven solutions efficiently. Whether you require rule engines for complex business logic or workflow automation, these tools are tailored to the Microsoft ecosystem.

Python Rule Engines

Python, known for its simplicity and versatility, offers several rule engine options for developers seeking to incorporate rule-based logic into their applications. Let's explore some prominent Python rule engines:

  1. Pyke: Pyke is a knowledge-based inference engine (expert system) that allows developers to build rule-based systems using the Python programming language. It is designed for creating rule-based expert systems and decision support systems. Pyke uses knowledge-based programming principles, where facts and rules are expressed in a human-readable format. This makes it accessible to both developers and domain experts.
  2. Python-rule: Python-rule is a lightweight and easy-to-use Python library for implementing rule engines. It offers a simple way to define rules and conditions in Python code. While it may not be as feature-rich as some other rule engines, it is well-suited for smaller-scale projects and applications where a more extensive rule engine might be overkill.
  3. Drools for Python: Drools, originally a Java-based rule engine, has a Python port that allows Python developers to benefit from its powerful rule capabilities. Drools provides a high-level language for expressing complex rules and offers advanced features such as rule templates, decision tables, and event-driven rule execution.

Here's a basic Python implementation:

class Rule:
    def should_run(self, data):
        raise NotImplementedError

    def execute(self):
        raise NotImplementedError

class ExampleRule(Rule):
    def should_run(self, data):
        return data.get('message') == 'hello'

    def execute(self):
        print("Rule executed: Message is hello")

class RuleEngine:
    def __init__(self):
        self.rules = [ExampleRule()]

    def run(self, data):
        for rule in self.rules:
            if rule.should_run(data):

if __name__ == "__main__":
    engine = RuleEngine()
    data = {'message': 'hello'}

Python rule engines like Pyke and python-rule are excellent choices when you want to harness the simplicity and readability of Python while implementing rule-based systems or decision-support logic. Additionally, Drools for Python is an option if you need a more comprehensive rule engine with a Python interface.

Now, here’s two most popular Open Source language specific rule engines:

Spring Boot Rule Engine

Spring Boot Rule Engine is a popular framework for building Java applications, and it provides various extensions and libraries for different purposes. When it comes to implementing a rule engine in a Spring Boot application, you have several options. Here, we'll explore some of the ways you can integrate rule engines into Spring Boot projects.

1. Drools with Spring Boot:

Drools, as mentioned earlier, is a powerful open-source rule engine. Integrating Drools with Spring Boot is a common choice for Java developers.
You can include Drools dependencies in your Spring Boot project and configure the Drools rule engine using Spring's configuration features.
With Drools in Spring Boot, you can define, manage, and execute complex business rules seamlessly.

2. Camunda BPM with Spring Boot:

Camunda is an open-source BPM (Business Process Management) platform that includes a rule engine. It's often used for workflow automation and decision management.
You can easily integrate Camunda BPM with Spring Boot to leverage its rule engine capabilities.
Camunda's rule engine allows you to define and manage business rules using the Decision Model and Notation (DMN) standard.

3. Drools Decision Tables with Spring Boot:

Drools provides a feature called "Decision Tables," which allows you to define rules in a tabular format.
You can create decision tables in Excel or CSV format, and Drools can interpret these tables to execute rules.
Integrating Drools Decision Tables with Spring Boot is a straightforward way to manage rules, especially if your rules are relatively simple and can be represented in tabular form.

4. Custom Rule Engine with Spring Boot:

In some cases, you might need to implement a custom rule engine tailored to your specific requirements.
Spring Boot provides the flexibility to create custom components and services, allowing you to build a rule engine that aligns perfectly with your application's needs.

When choosing a rule engine for your Spring Boot application, consider factors such as the complexity of your business rules, performance requirements, and ease of integration. Depending on your use case, you can select the most suitable rule engine or combination of engines to meet your application's needs.

Camunda Rule Engine

Camunda is an open-source platform for workflow automation, decision management, and process automation. It includes a powerful business rule engine that enables organizations to define, manage, and execute business rules effectively. Here's a brief overview of the Camunda rule engine:

  1. Decision Management: Camunda's rule engine is part of its broader decision-management capabilities. It allows businesses to model and execute decision logic using the Decision Model and Notation (DMN) standard. DMN provides a standardized way to define and represent decision-making processes.
  2. Integration with Processes: One of Camunda's strengths is its ability to integrate rules seamlessly with workflow and process automation. This means that decision rules can be incorporated directly into your business processes, ensuring that decisions are made consistently and in alignment with your processes.
  3. Decision Tables: Camunda supports decision tables, a tabular representation of decision logic. Decision tables are a user-friendly way to define complex rules, and Camunda provides tools for creating and managing these tables.
  4. Versioning and Auditing: Camunda offers version control and auditing features for decision rules. This is crucial for maintaining transparency and compliance in decision-making processes.
  5. Execution: Camunda's rule engine can execute decisions in real-time as part of workflow processes. It evaluates rules based on input data and produces the desired outcomes.
  6. Integration: Camunda seamlessly integrates with Spring Boot, making it a popular choice for Java developers building Spring Boot applications. This integration allows you to leverage Camunda's rule engine within your Spring Boot projects.
  7. Community and Support: Camunda has an active community and provides professional support options, making it a reliable choice for organizations of varying sizes.

In summary, Camunda's rule engine is a robust solution for decision management and automation. It excels in integrating decision rules with business processes and offers features like decision tables, versioning, and auditing. Whether you need to automate complex decisions or ensure consistency in your processes, Camunda is a valuable tool to consider.

Read Also: Business Rule Engine in Banking: Revolutionizing Financial Strategies

Best Open Source Rules Engines: A Comparison

When choosing an open source rules engine for your project, several factors come into play, including ease of use, flexibility, integration capabilities, and community support. Let's compare some of the best open-source rules engines based on these key parameters:

Rules Engine Ease of Use Flexibility Integration Community Support
Nools (Node.js) ⭐⭐⭐⭐ ⭐⭐⭐ ⭐⭐⭐⭐ ⭐⭐⭐
Drools (Java) ⭐⭐⭐⭐⭐ ⭐⭐⭐⭐ ⭐⭐⭐⭐⭐ ⭐⭐⭐⭐⭐
NRules (C#) ⭐⭐⭐⭐ ⭐⭐⭐⭐⭐ ⭐⭐⭐⭐ ⭐⭐⭐
Pyke (Python) ⭐⭐⭐ ⭐⭐⭐⭐ ⭐⭐⭐ ⭐⭐⭐
Camunda (Java) ⭐⭐⭐⭐ ⭐⭐⭐⭐⭐ ⭐⭐⭐⭐ ⭐⭐⭐⭐⭐

Nools (Node.js): Nools offers a user-friendly JavaScript-like syntax, making it accessible for Node.js developers. It's particularly suitable for real-time rule evaluation and execution.

Drools (Java): Drools stands out for its comprehensive set of tools, including decision tables, rule language, and a powerful inference engine. It excels in complex decision-making scenarios.

NRules (C#): NRules combines ease of use with flexibility, making it a good choice for C# developers. It supports both forward and backward chaining.

Pyke (Python): Pyke's knowledge-based approach is suitable for building expert systems. It uses human-readable facts and rules.

Camunda (Java): Camunda offers extensive decision management capabilities, integrates seamlessly with workflows, and supports decision tables.

Evaluate these engines based on your use case to determine which one aligns best with your needs.

Read Also: How are Rules Engines used in the Banking industry?

Differences between open-source and closed-source rules engines

Here's a comparison table highlighting the key differences between open-source and closed-source rules engines:

Aspect Open Source Rules Engines Closed Source Rules Engines
Licensing Typically licensed under open-source licenses (e.g., GPL, MIT) Proprietary licenses with associated costs and restrictions
Cost Generally free to use and modify Typically involves licensing fees and ongoing maintenance costs
Customization Highly customizable and adaptable to specific needs Limited customization options, may require vendor support
Community Support Strong open-source communities provide support and updates Vendor-driven support and updates
Transparency Full access to source code for transparency and auditing Proprietary code often lacks transparency
Flexibility Offers flexibility to tailor rules and workflows Limited flexibility, constrained by the vendor's offerings
Integration Supports integration with various systems and technologies Integration may be limited to specific platforms
Vendor Lock-In No vendor lock-in; users have control over the software Potential vendor lock-in, reliance on proprietary solutions
Scalability Scalability depends on the specific open-source project Scalability may vary; vendor-dependent
Updates and Maintenance Community-driven updates and maintenance efforts Vendor-driven updates and maintenance
Security Security relies on community contributions and audits Vendor may offer dedicated security resources
Support and Documentation Documentation and support may vary in quality and availability Vendor provides official documentation and support
Total Cost of Ownership (TCO) Lower TCO due to no licensing fees Higher TCO due to licensing and support costs

However, the choice between open-source and closed-source rules engines depends on specific business requirements, budget considerations, and the level of customization and control needed. Both options have their advantages and disadvantages, and organizations should carefully evaluate which aligns best with their objectives.


In conclusion, open-source rules engines offer a compelling alternative to closed-source counterparts, providing flexibility, cost-effectiveness, and transparency. These open-source solutions empower organizations to tailor rule management and execution to their unique needs while benefiting from vibrant open-source communities.

While open-source rules engines have their merits, it's crucial to consider factors such as licensing, support, and customization when making a decision. Whether opting for open source or closed source, the choice ultimately hinges on aligning the technology with the organization's goals and requirements.

As technology continues to evolve, the landscape of rules engines will evolve too. Staying informed about the latest developments and understanding the nuances of open and closed-source options will enable businesses to make informed decisions that drive their success.


Q1. Is Drools rule engine open source?

Yes, Drools is an open-source rule engine. It is a popular open-source business rule management system that allows you to define and manage complex business rules.

Q2. What is the alternative to Drools rule engine?

There are several alternatives to Drools rule engine, including:

  1. Camunda: An open-source platform that includes a business rules engine along with workflow and decision automation capabilities.
  2. IBM Operational Decision Manager (ODM): A comprehensive decision management solution that includes rule engine functionality.
  3. Red Hat Decision Manager: An open-source decision management platform that includes a rules engine and decision modeling tools.
  4. OpenRules: An open-source, business rules and decision management system for rule-based applications.
  5. Activiti: An open-source workflow and BPM platform that includes a rule engine for business process management.

Q3. Does Azure have a rules engine?

Yes, Azure provides Azure Logic Apps, which allows you to create workflows and automation processes that can include rules and conditions. While it may not be a dedicated rules engine like Drools, it can be used to implement rule-based logic in your Azure-based applications.

Q4. What is the open-closed principle rule engine?

The Open-Closed Principle is a concept in software engineering that suggests that software entities (such as classes, modules, and functions) should be open for extension but closed for modification. In the context of a rule engine, it means that the engine should allow you to add new rules or modify existing ones without changing the core engine's code. This principle promotes flexibility and maintainability in rule-based systems by enabling rule changes without disrupting the existing codebase. Rule engines like Drools often adhere to the Open-Closed Principle.

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