---
id: flagsmith-flag-engine
version: "10.2.0"
license: BSD3
license_treatment: permissive
maintenance: active
---

# flagsmith-flag-engine — Flag engine for the Flagsmith API.

License: permissive · Maintenance: active · Downloads: 1.0M/mo

## What it is and what it does

Flagsmith Flag Engine is the core evaluation runtime that powers the Flagsmith feature flag and remote configuration service. It takes flag definitions and rules, then evaluates them against user context to determine which flags are enabled and what configuration values apply. The engine is written in plain Python using Marshmallow schemas for data validation and serialization, making it lightweight and portable.

This package is the computational heart of Flagsmith's flag resolution logic. Rather than a full feature-flag management platform, it's the evaluation component—useful if you're integrating Flagsmith's flag logic into your own systems or running a custom deployment where you need the flag engine as a library. It depends on jsonpath-rfc9535 for JSONPath queries, semver for version comparisons, and typing-extensions for type hints.

Use it for:

- Embed flag evaluation logic into a custom Flagsmith deployment or private cloud instance
- Integrate remote configuration rule evaluation into an existing application without the full Flagsmith platform
- Build a feature flag service that reuses Flagsmith's proven evaluation semantics and rule engine
- Test flag rules and configurations offline using the engine as a library in your test suite

## Worth the install?

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

Evaluates feature flags and remote configuration rules using a lightweight, pure-Python engine that powers the Flagsmith API.

Yes, if you need Flagsmith's flag evaluation logic as a library component. The low install friction, active maintenance, permissive license, and zero known vulnerabilities make it safe to adopt. However, verify first whether you need the full Flagsmith platform or just this engine—it is a specialized component designed primarily to power the main Flagsmith API rather than a standalone feature-flag client.

## Install

pip install flagsmith-flag-engine
uv add flagsmith-flag-engine
poetry add flagsmith-flag-engine

## Installing flagsmith-flag-engine

Before you install: Low friction: pure Python wheel with only three runtime dependencies (jsonpath-rfc9535, semver, typing-extensions). Active maintenance with a recent release 66 days ago and commits through August 2026.

License in practice: BSD 3-Clause license permits commercial and private use with minimal restrictions; suitable for most projects.

Quickstart:

pip install flagsmith-flag-engine

from flagsmith_flag_engine import evaluate_flags
# Engine evaluates flags using Marshmallow schemas and plain Python

Verify before relying:

- Whether this engine is intended for standalone use or primarily as a dependency of the main Flagsmith API
- Performance characteristics or throughput limits for flag evaluation at scale
- Whether the engine handles all flag types and rule conditions that the full Flagsmith service supports

## Package facts

- License: BSD3 (permissive)
- Python support: unspecified
- Install friction: low
- Maintenance: active
- Downloads: 1.0M/month (top 5,000 on PyPI)
- Known vulnerabilities: none known

## Tags

feature flag evaluation engine, remote config flag engine, flagsmith flag evaluation, feature flag rules engine, flag evaluation library, remote configuration engine, feature-flags, remote-config

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