Unleash

Two API surfaces: Admin API for management and Client API for SDK evaluation. Admin API at {unleash-url}/api/admin/ covers features, strategies, projects, environments, segments, and API tokens. Feature toggle creation specifies type (release, experiment, operational, kill-switch, permission) and initial strategy. Strategy configuration uses parameters (percentage, userIds, hostNames) and constraints (attribute-based conditions). The Client API at /api/client/ provides feature configurations and accepts metrics. Feature toggle state is per-environment — a toggle can be enabled in staging and disabled in production. The API design is straightforward REST. Variants enable multivariate flags. Impression data tracks evaluation events. The Admin API follows standard CRUD patterns without the semantic patching complexity of LaunchDarkly.

Admin API errors return JSON with id, name, and message fields. Standard HTTP status codes. SDK evaluation resilience follows the same pattern as other local-evaluation platforms: SDKs cache configurations and continue evaluating during connectivity issues. The self-hosted model shifts reliability responsibility to the operator — database availability, API server health, and network connectivity are operational concerns. Unleash Edge provides a lightweight evaluation proxy for edge deployment. Metrics collection is best-effort — missed metrics don't affect evaluation. Rate limits on the Admin API depend on deployment configuration. The main reliability consideration for agents: self-hosted Unleash requires operational investment (database, backups, monitoring) that managed platforms handle automatically.

Unleash is the leading open-source feature flag platform, offering self-hosted deployment alongside Unleash Cloud. For agents, the open-source model means no vendor lock-in and the ability to inspect the evaluation engine. The core model uses feature toggles with activation strategies: standard (on/off), gradual rollout (percentage), user IDs, IP ranges, hostname, and custom strategies. Server-side SDKs (Node, Java, Python, Go, Ruby, .NET, PHP, Rust) evaluate locally with background polling for configuration updates. The Admin API covers feature toggle CRUD, strategy management, project/environment configuration, and metrics. For agents in environments requiring self-hosted infrastructure (compliance, air-gapped networks), Unleash is the primary option. The trade-off versus LaunchDarkly/Statsig: less polished experimentation and analytics, but full control over the infrastructure.

API tokens are typed: admin tokens (full management access), client tokens (read-only for SDK evaluation), and frontend tokens (for browser/mobile SDKs with CORS). Tokens can be scoped to specific projects and environments. The self-hosted model means the authentication infrastructure is under the operator's control — custom auth providers, SSO integration, and network-level security are all configurable. Unleash Cloud provides managed authentication. For agents, the token typing provides good separation: SDK evaluation tokens can't modify flags, and admin tokens can be project-scoped. The open-source edition has simpler auth; the enterprise edition adds SSO, SCIM, and custom roles. No OAuth for API integrations — token-based auth throughout.

Documentation at docs.getunleash.io covers self-hosted deployment, API reference, SDK guides, and conceptual explanations. The Admin API reference is comprehensive with endpoint descriptions and examples. SDK documentation covers each language with initialization, evaluation, and metric reporting guides. The open-source community contributes SDKs, integrations, and deployment guides. GitHub repository provides source code access and issue tracking. The documentation balances self-hosted deployment concerns (database setup, configuration, monitoring) with feature management concepts. For agents, the deployment documentation is essential for self-hosted setups. Unleash's documentation quality has improved significantly — earlier versions had gaps, but the current docs are solid for both cloud and self-hosted paths.