---
id: openfeature-flagd-core
version: "1.0.0"
license: Apache License Version 2.0, January 2004 http://www.apache.org/licenses/ TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 1. Definitions. "License" shall mean the terms and conditions for… (full text in the JSON record)
license_treatment: permissive
maintenance: active
---

# openfeature-flagd-core — OpenFeature flagd evaluator core implementation

License: permissive · Maintenance: active · Downloads: 208.9K/mo

## What it is and what it does

openfeature-flagd-core is a reference implementation of the flagd evaluator for the OpenFeature Python SDK contrib project. It parses flag definitions, applies targeting rules written in JSON logic, and resolves flag variants using custom operators for fractional rollouts, semantic version comparisons, and string matching. The package provides the core evaluation engine that sits between flag definitions and the OpenFeature SDK, handling the logic of determining which variant a flag should return given its configuration and evaluation context.

The package is designed as a modular component mirroring the Java flagd-core module, making it suitable for projects that need deterministic flag evaluation without external service dependencies. It depends on openfeature-sdk for the broader SDK integration, plus mmh3 for hashing (likely for fractional rollouts), panzi-json-logic for rule evaluation, and semver for version comparisons.

Use it for:

- Evaluate feature flags locally in Python applications using JSON logic targeting rules without requiring a remote flagd service.
- Implement fractional rollouts and canary deployments by resolving flag variants based on custom operators and context.
- Test flag evaluation logic in unit tests by directly instantiating and configuring the evaluator with flag definitions.
- Build custom feature flag management systems that need a reference-grade evaluator compatible with the OpenFeature specification.
- Resolve semantic version-based feature flags for version-gated functionality or compatibility checks.

## Worth the install?

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

Evaluates feature flags using JSON logic and custom operators (fractional, semantic versioning, string matching) as a reference implementation for the OpenFeature flagd evaluator.

Yes, if you are building on the OpenFeature Python SDK and need local flag evaluation. The package is actively maintained, has low install friction, carries a permissive Apache 2.0 license, and has no known vulnerabilities. Install only if you are already adopting OpenFeature; it is a specialized component, not a general-purpose library.

## Install

pip install openfeature-flagd-core
uv add openfeature-flagd-core
poetry add openfeature-flagd-core

## Installing openfeature-flagd-core

Before you install: Low install friction with a pure-Python wheel distribution. Actively maintained with recent commits; part of the OpenFeature Python SDK contrib ecosystem.

License in practice: Apache 2.0 permissive license allows commercial and derivative use with attribution and notice requirements; suitable for most projects.

Quickstart:

pip install openfeature-flagd-core

from openfeature.contrib.tools.flagd.core import FlagdCore

core = FlagdCore()
core.set_flags('{"flags": {"my-flag": {"state": "ENABLED", "variants": {"on": true}, "defaultVariant": "on"}}}')
result = core.resolve_boolean_value("my-flag", False)

Requires Python 3.10 or later.

Verify before relying:

- Whether the package supports flag evaluation with context/targeting rules beyond the basic boolean resolution shown in the example.
- Performance characteristics when evaluating large flag sets or complex JSON logic expressions.
- Integration patterns with the broader OpenFeature SDK beyond the core evaluator role.

## Package facts

- License: Apache License Version 2.0, January 2004 http://www.apache.org/licenses/ TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 1. Definitions. "License" shall mean the terms and conditions for… (full text in the JSON record) (permissive)
- Python support: supports_current
- Install friction: low
- Maintenance: active
- Downloads: 208.9K/month (top 15,000 on PyPI)
- Known vulnerabilities: none known

## Tags

feature flag evaluation, flagd core implementation, JSON logic flag targeting, openfeature flag resolver, flag variant resolution, feature flag rules engine, flag state evaluation, feature-flags, openfeature, flag-evaluation

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