Flagr
Open source feature flagging, A/B testing and dynamic configuration microservice
Founded
2018
Starting Price
$0
Category
Developer Tools
Last updated April 27, 2026
About Flagr
Flagr is an open source Go microservice for feature flagging, A/B testing, and dynamic configuration. Originally developed by Checkr, it delivers the right experience to the right entity and monitors the impact through clean REST APIs.
Pros & Cons
Pros
- Completely free and open source with no usage limits
- Written in Go for high performance and low resource usage
- Simple Docker deployment gets you running in minutes
- Clean REST API with Swagger documentation
- Supports data export to major cloud platforms for analytics
Cons
Key Features
Feature Flags
Toggle features on and off for specific users, segments, or percentages without code deployments
A/B Testing
Run experiments with variant distributions and monitor impact on key metrics
Dynamic Configuration
Change application configuration at runtime without redeploying services
REST API
Clean Swagger-documented REST APIs for flag management and evaluation
Docker Deployment
Easy deployment with a single Docker command, up and running in minutes
Data Export
Export evaluation data to AWS Kinesis, Google Cloud Pub/Sub, and Kafka for analytics
Web UI
Built-in management dashboard for creating and managing flags and experiments
Pricing
Open Source
$0
- Unlimited flags
- A/B testing
- Dynamic configuration
- REST API
- Docker deployment
Best For
Feature Rollouts
Gradually roll out new features to a percentage of users to minimize risk
A/B Testing
Run controlled experiments to measure the impact of UI or feature changes
Runtime Configuration
Dynamically adjust application settings without redeployment
Kill Switches
Instantly disable problematic features in production without a code change
