Unleash

What Unleash does

Unleash is a feature flag server with a web admin UI, a REST API and official SDKs for backend, frontend and mobile platforms. Each flag has one or more activation strategies, such as a gradual rollout to a percentage of users, with constraints on context fields like user ID, environment or a custom property. Segments let you reuse a set of constraints across flags, and stickiness keeps a user in the same bucket as a rollout grows.

Flags can also carry variants, which is how Unleash handles simple A/B tests. It assigns users to variants but does not compute experiment results; you send the exposure to your own analytics tool and analyze it there.

The admin UI flags stale toggles and shows technical debt, which helps teams remove flags once a feature is fully released.

How evaluation works

Backend SDKs download the full flag configuration and evaluate flags locally in memory, so the user context you pass in never leaves your application. They refresh the configuration on a short polling interval, so a change takes effect after a small delay rather than instantly.

Frontend and mobile SDKs work differently: they send the context to the Unleash server, or to the Unleash Edge proxy, and receive the evaluated flags. The open source Edge proxy is MIT-licensed but in long-term maintenance, with end of life set for 31 December 2026; its successor, Enterprise Edge, is commercial. Teams that self-host and need a proxy for frontend traffic should plan for that.

Self-hosting Unleash

The open source edition is a single Node.js service with PostgreSQL. The documented setup uses Docker Compose; the docs require PostgreSQL 15 or later and Node.js 22 or later when running from source. By default a self-hosted instance checks for new versions and sends an anonymous instance ID; you can turn this off with an environment variable.

The open source edition is free and has no seat limit, but it is capped at 1 project, 2 environments and 5,000 flags per instance. Single sign-on, SCIM provisioning, granular role-based access control and change request approvals are only in Unleash Enterprise, which can also be self-hosted with a commercial license.

Flag configuration can be exported and imported as JSON, which makes it possible to move between instances or from self-hosted to hosted.

Hosted version

The company hosts Unleash Enterprise as a paid service, billed per seat or under an annual contract, with a 14-day trial and a choice of US or EU data residency. There is no free hosted plan; the free option is self-hosting the open source edition.

Limitations

The project and environment caps are the main constraint: a team with several products, or with separate development, staging and production environments, will reach them quickly. The AGPL license matters if you modify Unleash and offer it to others over a network. There are no built-in experiment statistics, and the end of life of the open source Edge proxy reduces options for self-hosted frontend traffic.

Who it suits

Unleash fits engineering teams that want a well-established flag server for one product, with local evaluation in backend services and SDKs for most languages. Larger organizations that need several projects, SSO and approval workflows will end up on the Enterprise edition. If you need experiment analysis, compare GrowthBook; if you want a permissive license, compare Flagsmith.