---
id: openfeature-flagd-api
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-api — OpenFeature flagd evaluator API definition

License: permissive · Maintenance: active · Downloads: 208.6K/mo

## What it is and what it does

This package provides the pure API contract—a Python Protocol—that defines what a flagd evaluator must implement to work with the OpenFeature SDK. It is a lightweight interface definition rather than a working implementation, intended for developers who want to create custom evaluators for the flagd provider. The package depends only on openfeature-sdk and is part of the OpenFeature Python SDK contrib project, mirroring the Java flagd-api module.

You install it when you need to build your own evaluator implementation that conforms to the flagd contract. It establishes the protocol boundary between the OpenFeature framework and custom evaluation logic, allowing third-party code to plug in without modifying the core SDK.

Use it for:

- Building a custom flagd evaluator implementation that integrates with the OpenFeature SDK.
- Defining type-safe contracts for feature flag evaluation in a larger OpenFeature architecture.
- Creating a domain-specific evaluator that implements the Evaluator protocol for specialized flag resolution logic.
- Extending the OpenFeature ecosystem with evaluators that handle flagd-compatible feature flag formats.

## Worth the install?

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

Defines the Python Protocol contract for flagd evaluators, allowing custom implementations to integrate with the OpenFeature SDK.

Yes, if you are building a custom flagd evaluator for OpenFeature. This is a pure contract package with no vulnerabilities, permissive licensing, and active maintenance. Install only if you need to implement the Evaluator protocol; it is not a standalone tool but a dependency for evaluator development.

## Install

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

## Installing openfeature-flagd-api

Before you install: Low install friction with a single runtime dependency on openfeature-sdk. Actively maintained as of 2026-08-12 with recent activity.

License in practice: Apache 2.0 permissive license allows commercial and private use, modification, and distribution with minimal restrictions—only requiring license and copyright notice preservation.

Quickstart:

pip install openfeature-flagd-api

from openfeature.contrib.tools.flagd.api import Evaluator, FlagStoreException

# Implement the Evaluator protocol for custom evaluator

Requires Python 3.10 or later.

Verify before relying:

- Whether the package includes concrete example implementations or reference evaluators beyond the protocol definition.
- API stability guarantees or semantic versioning policy for the protocol contract.
- Integration testing guidance or compatibility matrix with specific flagd versions.

## 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: 208.6K/month (top 15,000 on PyPI)
- Known vulnerabilities: none known

## Tags

flagd evaluator protocol, openfeature flag evaluation api, feature flag provider interface, flagd custom evaluator, openfeature contrib tools, flag evaluation contract, flagd api definition, feature-flags, openfeature, protocol-definition

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