Rollout Simulator
Simulate percentage-based feature flag rollouts. See exactly which users will be included using consistent hashing — the same algorithm used in production.
Percentage Rollout Simulation
User Bucket Lookup
Check which rollout bucket a specific user falls into (0-99). If bucket < rollout percentage, the user is included.
Free API Endpoints
These endpoints are free, no API key required. Rate limited to 60 requests/hour.
/api/v1/rollout/simulate?percentage=25&count=100
Simulate a percentage rollout across N users
/api/v1/rollout/bucket?user_id=usr_123
Get the rollout bucket (0-99) for a specific user
/api/v1/evaluate-playground
Evaluate feature flag rules without an account
curl -X POST https://flagbit.anethoth.com/api/v1/evaluate-playground \
-H "Content-Type: application/json" \
-d '{"flags":{"dark_mode":{"enabled":true,"rules":[]}}, "context":{"plan":"pro"}}'
FAQ
What is consistent hashing in feature flags?
Consistent hashing ensures the same user always gets the same rollout decision. FlagBit uses MD5 hashing on the user identifier, mapping to a bucket 0-99. If your rollout is 25%, users in buckets 0-24 are included. When you increase to 50%, the original 25% stay included and buckets 25-49 are added.
Why doesn't the actual percentage exactly match the target?
Hash distribution is approximately uniform but not perfectly so for small sample sizes. With 100 users and a 25% rollout, you might see 23% or 27% actually included. The distribution converges to the target as sample size increases. Try with 1000 users to see more accurate results.
Can I use these APIs in production?
The free utility APIs are rate-limited to 60 requests/hour. For production feature flag evaluation, sign up for a free FlagBit account to get an API key with much higher limits and full flag management.
How do targeting rules work?
Targeting rules let you enable features for specific users based on attributes. Supported operators: eq (equals), neq (not equals), contains, in (value in list), and percent (percentage rollout). Try the evaluate playground API to test rules interactively.
Ready for production feature flags?
Free tier includes 1 project, 10 flags, and 1,000 evaluations/day.
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