Flagr is an open-source service written in Go that helps deliver the right user experience to the right users and monitor the results.
It combines the functionality of feature flags, A/B testing, and dynamic configuration, providing a convenient REST API for flag management and evaluation.
Why Use Flagr
Flagr simplifies the process of deploying and controlling new features in applications.
Developers can safely enable or disable features, run experiments, and analyze their impact - all without restarting the service.
- Feature flags: flexible control of functionality without redeploy;
- A/B testing: run experiments and collect analytics by user groups;
- Dynamic config: adjust application parameters in real time;
- REST API: simple interface for integration with any language or system.
How Flagr Works
Flagr stores all flags and experiments in a database and provides an API for their evaluation.
Clients (applications, services, microservices) request a flag value for a specific user or context, and Flagr returns the appropriate configuration.
Usage Example
# Get flag value via API
curl -X POST "http://localhost:18000/api/v1/evaluation" \
-H "Content-Type: application/json" \
-d '{
"entityID": "user123",
"entityType": "user",
"flagKey": "new_ui"
}'If the new_ui flag is active for that user, the application can display the new interface version.
Thus, Flagr allows you to test features safely and react quickly to results.
Where You Can Use Flagr
- In web and mobile applications - for gradual rollout of new features;
- In microservice architectures - to control the behavior of individual services;
- In large teams - to safely run experiments without affecting all users.
Advantages
- Open source and free to use;
- Supports A/B tests, feature toggles, and configuration management in one solution;
- Easy integration via REST API;
- Comprehensive documentation and a web interface for managing flags.
FAQ
- What is a feature flag?
A feature flag is a mechanism that allows enabling or disabling application features without changing the code.
It helps safely test new functionality. - Is Flagr suitable for production?
Yes, Flagr is used in production by many companies and supports horizontal scaling and high availability. - Can Flagr be integrated with other languages?
Absolutely. Flagr provides a REST API that can be called from any application - in Python, Go, Java, JavaScript, and more. - Does Flagr have a user interface?
Yes, Flagr includes a web interface for managing flags, creating experiments, and tracking metrics. - How to get started quickly?
Run Flagr with Docker:docker run -p 18000:18000 checkr/flagrAfter launch, the interface will be available at http://localhost:18000.
