I Built a Lightweight Rule Engine for JS, C#, and Dart — Here's How It Works

Berat ARPA — Sat, 21 Feb 2026 00:04:44 +0000

The Problem
I kept running into the same pattern across different projects: events happen, some conditions need to be checked, and based on those conditions, certain actions should execute. Authentication flows, game mechanics, IoT automation, e-commerce logic — they all follow this pattern.

Most rule engines I found were either too heavy for what I needed or locked into a single language. So I built my own.

What is ARE?
ARE (Action Rule Event) is a lightweight, dependency-free rule engine. The concept is straightforward:

Events — Things that happen (user logs in, temperature changes, order placed)
Rules — Conditions to evaluate (if temperature > 30, if order total > 100)
Actions — What to execute when conditions are met (send notification, apply discount)
The pipeline: Event → Middleware → Condition Evaluation → Rule Matching → Action Execution

Multi-Platform
I wanted this to work wherever I work, so ARE is available on three platforms:

JavaScript/TypeScript → npm
C# / .NET → NuGet
Dart / Flutter → pub.dev
Same API design across all three. If you know one, you know them all.

The Playground
Documentation is fine, but I wanted people to actually feel how the engine works. So I built an interactive playground with three real-world scenarios:

🎮 RPG Game — Combat rules, loot drops, zone effects, boss battles
🏠 Smart Home — Sensor events, schedules, energy management, security
🛒 E-Commerce — Order processing, inventory alerts, customer rewards

Each scenario comes with pre-configured events, rules, and actions. You fire an event and watch the engine process it in real time.

Features I'm proud of:
Rule Flow Diagram — An animated pipeline showing each stage of processing

Rule Debugger — Expand any rule to see a condition-by-condition breakdown: what field was checked, what operator was used, what was expected vs. actual, and whether it passed or failed

Relationship Graph — A visual map showing how events connect to rules and rules connect to actions. Hover over any node and see its connections highlighted

Interactive Tutorial — A guided tour for first-time visitors that walks through every panel

Full CRUD — Add, edit, or delete events, rules, and actions on the fly. Create your own scenarios without writing code

Code Sandbox — Write your own ARE logic from scratch with a Monaco editor

🔗 Try it: are-playground.netlify.app

Tech Stack
React 19 + TypeScript
Vite
Tailwind CSS v4
Zustand for state management
Framer Motion for animations
i18next (English + Turkish)
What's Next
I'm looking for feedback. If you try the playground, I'd love to know:

Is the event → rule → action concept clear?
What use cases would you apply this to?
What's missing that would make this useful for your projects?
GitHub: github.com/BeratARPA/ARE

Thanks for reading. Happy to answer any questions.

DEV Community: Berat ARPA

I Built a Lightweight Rule Engine for JS, C#, and Dart — Here's How It Works