Unleash/unleash

What it is

Unleash is an open-source feature management server. Instead of redeploying an application to change what users see, teams check feature flags through an SDK and let the server decide which flags are on, for whom, and in which environment. Typical uses are gradual rollouts and canary releases, kill switches, A/B tests, and staging-production environments.

The server is API-first, so flag state can be managed and automated programmatically. The project ships official backend and frontend SDKs for languages such as Go, Java, Node.js, Python, .NET, Rust, Android, Flutter, iOS, JavaScript, React, Svelte, and Vue, plus community SDKs. It is aimed at development and platform teams that already run a deployment pipeline and want release control separate from it.

Quick start

With Git and Docker installed, run:

git clone git@github.com:Unleash/unleash.git
cd unleash
docker compose up -d

Open http://localhost:4242 and log in with admin / unleash4all. Then pick an SDK from the official SDK list and configure it against the local instance:

• Frontend SDKs: URL http://localhost:4242/api/frontend/ and client key default:development.unleash-insecure-frontend-api-token
• Backend SDKs: Unleash API URL http://localhost:4242/api/ and token default:development.unleash-insecure-api-token

A flag check is a single SDK call; for example in Java:

if (unleash.isEnabled("AwesomeFeature")) {
  // do new, flashy thing
} else {
  // do old, boring stuff
}

If you only want to look around, the live demo runs without signup. To run from source with Node.js instead of Docker, follow the contributing guide.

Constraints

• The local Docker Compose setup uses default credentials and insecure development tokens; do not reuse them as a production configuration.
• Self-hosting in production requires a persistent server; configuration and scaling guidance is in the self-hosting documentation and the configuration reference.
• The open-source server is licensed AGPL-3.0. Features including RBAC, change requests, SSO, SCIM, and multiple environments are positioned as Pro/Enterprise offerings.
• Unleash Edge is the separate proxy layer for serving large numbers of frontend clients without loading the main server.

HotRepo's take

In the daily TypeScript ranking record for 2026-11-07, the repository gained 180 stars and reached position 7. A same-week Hacker News thread, "We've built an open-source feature flag server for 11 years," drew 156 points and 104 comments. The discussion is more about product framing than implementation: one commenter describes moving from "I can build that myself" to seeing why people pay for it sgt, 2026-11-06, while another says after several years of daily use, the tool does what you expect without getting in the way Rant423, 2026-11-07.

The underlying tension raised in the thread — whether flags need a platform or can stay as environment state in a deploy pipeline kalcode, 2026-11-06 — is the real adoption question for this project: a self-hosted server is worth its operational cost when non-engineering users or targeted rollouts need to control flags without a deployment.