---
id: zen-engine
version: "0.53.0"
license: unclear
license_treatment: unclear
maintenance: active
---

# zen-engine — Open-Source Business Rules Engine

License: unclear · Maintenance: active · Downloads: 371.1K/mo

## What it is and what it does

zen-engine is a Python wrapper around a Rust-based business rules engine designed to execute decision models expressed as JSON. It parses JSON Decision Model (JDM) files—which represent decision logic as interconnected graphs of nodes (decision tables, switches, functions, expressions)—and evaluates them against input data to produce structured results. The engine is embeddable and designed for applications that need to externalize decision logic into declarative, editable models rather than hard-coded conditionals.

Typical usage involves creating a ZenEngine instance, loading a JDM from JSON (either directly or via a custom loader function), and calling evaluate() with input data. The loader pattern allows you to fetch JDM definitions from files, databases, APIs, or other sources at runtime. No runtime dependencies are required beyond the compiled zen-engine wheel itself.

Use it for:

- Implement tiered pricing or fee logic that changes frequently without code redeployment
- Build eligibility or approval workflows where rules are managed by business analysts
- Evaluate complex conditional logic in lending, insurance, or compliance workflows
- Load decision models from a remote service or database and execute them in-process
- Prototype decision logic visually using the JDM editor, then execute it in production

## Worth the install?

AI-flagged interpretation of the facts above — verify before relying.

zen-engine is a Python binding for a Rust-based business rules engine that loads and executes JSON Decision Models (JDM) to evaluate complex decision logic.

Yes, if you need to externalize and version decision logic separately from code. The package is actively maintained, has no known vulnerabilities, and offers broad platform coverage. The main caveat is that the license is undeclared in package metadata—verify the actual license in the repository before adopting it in proprietary work. Install friction is moderate due to compiled wheels, but prebuilt binaries are available for common platforms.

## Install

pip install zen-engine
uv add zen-engine
poetry add zen-engine

## Installing zen-engine

Before you install: Medium install friction due to compiled wheels; the package provides prebuilt binaries for Python 3.10–3.14 across Linux (aarch64, x86_64), macOS (Intel and ARM), and Windows. Maintenance is active with recent releases and a healthy repository (1907 stars, last commit 2026-08-07).

License in practice: License status is unclear—no SPDX identifier or raw license text is available in the package metadata. Verify the actual license terms in the repository before using in proprietary or restricted contexts.

Quickstart:

pip install zen-engine

import zen

with open("./decision_model.json", "r") as f:
    content = f.read()

engine = zen.ZenEngine()
decision = engine.create_decision(content)
result = decision.evaluate({"input": 15})

Requires Python 3.7 or later; prebuilt wheels are available for Python 3.10–3.14 on Linux, macOS, and Windows.

Verify before relying:

- Actual license terms and restrictions (not declared in package metadata)
- Performance characteristics and scalability limits for large decision graphs
- Whether the loader pattern supports concurrent or async evaluation

## Package facts

- License: not declared (unclear)
- Python support: supports_current
- Install friction: medium
- Maintenance: active
- Downloads: 371.1K/month (top 15,000 on PyPI)
- Known vulnerabilities: none known

## Tags

business rules engine python, decision table evaluation, json decision model executor, rule engine bre, decision logic evaluation, rules-based decision making, jdm engine python, decision-engine, rules-engine, rust-binding

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