What is Flagr?

Flagr is an open-source Go service for feature flags, A/B tests, and dynamic configuration. Your app calls POST /api/v1/evaluation with who is asking (entityID, entityContext); Flagr returns a variant and optional JSON attachment.

That lets you ship code dark and turn it on per audience, run experiments with sticky assignment, and change runtime config without redeploying. Self-hosted (SQLite, MySQL, PostgreSQL, or JSON/GitOps) with a Vue 3 UI and an official Docker image.

openflagr/flagr continues development from the original checkr/flagr.

Quick start

docker pull ghcr.io/openflagr/flagr
docker run -it -p 18000:18000 ghcr.io/openflagr/flagr

open http://localhost:18000

Hosted demo: try-flagr.onrender.com (may cold-start)

curl -sS -X POST https://try-flagr.onrender.com/api/v1/evaluation \
  -H 'content-type: application/json' \
  -d '{
    "entityID": "127",
    "entityType": "user",
    "entityContext": { "state": "NY" },
    "flagID": 1,
    "enableDebug": true
  }'

Docs

Documentation covers integration, self-hosting, environment variables, and the API reference.

Performance

vegeta load test (~2k req/s, sub-ms median in published run):

Requests      [total, rate]            56521, 2000.04
Duration      [total, attack, wait]    28.26s, 28.26s, 365.53µs
Latencies     [mean, 50, 95, 99, max]  371.63µs, 327.99µs, 614.92µs, 1.39ms, 12.50ms
Success       [ratio]                  100.00%
Status Codes  [code:count]             200:56521

Clients

Language	Client
Go	goflagr
JavaScript	jsflagr
Python	pyflagr
Ruby	rbflagr

Contribute

Issues and pull requests: Contributing. Local commands and code layout: AGENTS.md (make help).

License

Apache 2.0 (openflagr/flagr, original checkr/flagr).