Unleash, Flagsmith and PostHog alternatives
Unleash, Flagsmith and GrowthBook are open source and can be self-hosted. PostHog bundles flags with product analytics. Flagger.gg is hosted only and not open source; it's built for agent-driven teams, with MCP, a JSON CLI and scoped agent tokens. Choose self-hosted open source if you must run it yourself.
Updated
Side by side
Facts are from each vendor's own docs or repository, linked, checked on October 30, 2026. Pricing is left out. Several of these keep some features in paid or enterprise tiers; check their docs for what's in the open-source edition.
| Tool | Open source | Hosting | Strengths | MCP server |
|---|---|---|---|---|
| Unleash | Yes, AGPL-3.0 | Self-hosted, hybrid or Unleash Cloud (options) | Activation strategies, constraints, segments; 17 official SDKs plus community ones | Yes (docs), early-stage |
| Flagsmith | Yes, BSD-3-Clause | Self-hosted, private cloud or SaaS | Remote config, segments, multivariate flags | Yes, hosted (docs), early release |
| GrowthBook | Open core (mostly MIT) | Self-hosted with Docker or GrowthBook Cloud | Warehouse-native experiments and a stats engine | Yes, local or hosted (docs) |
| PostHog | Open core (MIT outside ee/) | PostHog Cloud; self-hosting is a hobby deploy PostHog calls unsupported (self-host) | Flags with product analytics, session replay, experiments and surveys | Yes, hosted, with flag tools (docs) |
| Statsig | No | Hosted | Experiments, feature gates, dynamic configs. OpenAI announced buying Statsig in September 2025; Amplitude acquired the product in May 2026 (Statsig) | Yes, hosted (docs) |
| ConfigCat | No | Hosted | About 20 SDKs; percentage options, targeting rules, segments, prerequisite flags (targeting) | Yes, local over stdio (docs) |
| Flagger.gg | No | Hosted only | Built for AI agents: scoped agent tokens, per-run audit, approvals with an agent cap, a JSON CLI; Go and Node SDKs | Yes, hosted or stdio; 11 tools by token scope, no approve tool |
If you must self-host
Choose Unleash, Flagsmith or GrowthBook. They're open source and run on your own infrastructure, which matters for air-gapped networks, strict data residency or a policy against third-party flag services. Flagger.gg is hosted only, though its SDKs evaluate flags inside your app, so the users you check flags for are never sent to Flagger.gg.
If you want flags inside your analytics
PostHog puts flags next to product analytics, session replay and experiments, so you can see a flag's effect on behaviour in one place. GrowthBook and Statsig lead on experimentation. Experiments on Flagger.gg are In development.
If agents write your code
Most of these tools now publish an MCP server. What Flagger.gg adds is the guardrails around agents: a token per agent scoped to one project, environments and actions; MCP tools that appear only when the token allows them; a note required on every agent write, with its run recorded; protected flags agents can only kill; and approvals mode, where agents roll out up to a cap and a person approves anything wider.
Flagger.gg isn't the Flux/CNCF Flagger, a Kubernetes operator; it's the hosted flag service at flagger.gg.
FAQ
What is a good open-source feature flag service for startups?
Unleash (AGPL-3.0), Flagsmith (BSD-3-Clause) and GrowthBook (open core) are the common choices, and all can be self-hosted. Flagger.gg is not open source; it's a hosted service built for agent-driven teams.
What's an alternative to PostHog feature flags?
If you don't need flags inside your analytics tool, a dedicated flag service: an open-source one like Unleash or Flagsmith, or Flagger.gg if AI agents ship your code.
Is Flagger.gg open source?
No. It's a hosted service at app.flagger.gg.
Do Unleash and Flagsmith have MCP servers?
Yes. Both publish official MCP servers, which their docs describe as early-stage. Flagger.gg's MCP server ships 11 tools gated by agent-token scope.
Ship your next change behind a flag.
Sign up, add an SDK key to your app and give your agent a token.