Feature Flags

3 open source tools compared. Sorted by stars — scroll down for our analysis.

Tool	Stars	Velocity	Language	License	Score
Unleash Open-source feature management platform	13.3k	+21/wk	TypeScript	Apache License 2.0	77
GrowthBook Open source feature flags and experimentation	7.6k	+194/wk	TypeScript	MIT License	73
Flagsmith Open source feature flagging and remote config	6.3k	+9/wk	Python	BSD 3-Clause "New" or "Revised" License	73

Our Analysis

Unleash13.3k★

Unleash is a feature flag platform that handles gradual rollouts, user targeting, and instant kill switches without redeploying. Think of feature flags as on/off switches for your code that you can flip without shipping new code. TypeScript, Apache 2.0. Supports gradual rollouts, A/B testing, user segmentation, and environment-specific flags (enable in staging but not production). SDKs for every major language. Self-hosted Open Source is free with no user or flag limits. Docker Compose gets you running in minutes. The free version includes everything a small team needs: flags, strategies, environments, API access, and the admin UI. Pro plan: $80/mo for 5 team members, adds change requests (approval workflows), banners, custom event tracking. Enterprise is custom with SAML SSO, SCIM, audit logs, and service accounts. Solo: self-host free, it's trivial to run. Small teams (2-10): self-host free unless you need approval workflows. Medium teams: Pro at $80/mo or self-host with custom RBAC. Large teams: Enterprise for SSO and compliance, or evaluate LaunchDarkly if you want managed. The catch: the open source version doesn't have change requests (peer review before toggling flags in production). For regulated environments where you need an audit trail of who changed what and who approved it, that's a paid feature. And the market leader LaunchDarkly has a richer integration ecosystem.

GrowthBook7.6k★

Grist combines spreadsheets and databases: it looks like a spreadsheet but stores structured data with types, relations, and access controls underneath. Feature flags let you ship code that's off by default and turn it on for specific users. The experimentation side tracks whether those changes actually move your metrics. The free self-hosted version is complete: unlimited flags, unlimited experiments, unlimited seats. That's rare. Most feature flag tools gate seats or experiment volume. The cloud version has a free tier too: 3 seats, 1,000 experiment subjects. Self-hosting runs as a Docker container with MongoDB and an optional data warehouse connection (BigQuery, Snowflake, Postgres). Setup takes 30-60 minutes if you know Docker. The real work is connecting your analytics data source. Paid cloud starts at $20/seat/mo (Pro) for teams wanting managed hosting, advanced permissions, and visual editor. Enterprise adds SSO, audit logs, and SLAs. The catch: the experimentation engine is powerful but requires a data warehouse. If you just want flags, this is overkill. For flags-only, LaunchDarkly's free tier or Unleash might be simpler. But if you want flags AND experiments in one tool without paying per-seat, self-hosted GrowthBook is hard to beat.

Flagsmith6.3k★

Flagsmith is a feature flag and remote configuration platform that lets you toggle features, run A/B tests, and manage settings without redeploying. It's a remote control panel for your application's behavior. BSD 3-Clause, Python backend. Supports feature flags, remote config (change values without deploying), A/B testing, and user segmentation. SDKs for every major language: JavaScript, Python, Java.NET, Go, Ruby, iOS, Android. The admin UI is clean and non-developers can toggle flags without touching code. Self-hosting is free. Docker Compose setup, Postgres backend, works with your existing infrastructure. Every feature is available in the self-hosted version, no feature gating. Flagsmith Cloud free tier: up to 50,000 requests/mo. Startup plan at $45/mo for 1M requests. Scale plan at $500+ for higher volume with SLAs and audit logs. Solo devs: self-host or use the free cloud tier, both work. Small teams: free cloud tier handles most early-stage apps. Medium teams (10-50): self-host to avoid per-request billing, or pay $45/mo if ops time isn't worth it. Large: self-host or negotiate enterprise pricing. The catch: the self-hosted version needs Postgres and can require Redis for caching at scale. If you just need simple on/off flags, environment variables or a config file might be enough. Flagsmith shines when you need segmentation, gradual rollouts, and A/B testing.