Flagsmith

Flagsmith is an open-source feature flagging, remote configuration, and A/B testing platform released under the BSD-3-Clause license. It lets engineering teams wrap any section of code behind a flag, then toggle, target, or gradually roll out that feature to specific environments, users, or segments, all without a redeploy.

Beyond simple on/off toggles, Flagsmith supports multivariate and A/B testing through its segments system: teams define user segments by custom traits and run split tests to measure feature impact before a full rollout. Organisation, project, and role structures keep multi-team setups organised, and 15+ official SDKs cover web, mobile, and server-side languages including TypeScript, Python, .NET, Java, and React/Next.js.

Under the hood, Flagsmith pairs a Django/DRF API (api/) with a Next.js/React frontend (frontend/), and ships a dedicated edge_api service for low-latency flag evaluation at the edge. The whole stack deploys via a single docker-compose up, which bootstraps an admin user, organisation, and project automatically for a fast path from clone to running instance.

The project has an active community (6,400+ stars, 140+ contributors) and integrates with common observability and analytics tools such as Datadog, Segment, Amplitude, and Rudderstack out of the box. Enterprise-tier features like SAML/SCIM SSO and extended governance require a commercial license, whether self-hosted or via the hosted SaaS at flagsmith.com.

What You Get

• Feature flags and remote config toggled per environment without a deploy
• Multivariate and A/B testing via user segments and custom traits
• 15+ official SDKs (TypeScript, Python, Java, .NET, React, Next.js, and more)
• Organisation/project/role structure for multi-team governance
• Edge-network flag evaluation service (edge_api) for low-latency reads
• One-command Docker Compose self-hosting setup

Common Use Cases

• Rolling out a risky feature to a small percentage of production traffic before a full launch
• Running an A/B or multivariate test on page copy using segment-based targeting
• Giving beta testers early access to unreleased features via user segments
• Toggling a feature off instantly in production without a code deploy or rollback
• Centralizing remote config values (rate limits, UI copy) across web, mobile, and server clients

Under The Hood

Architecture Flagsmith is a modular Django REST Framework API (api/) with domain-separated Django apps for organisations, projects, environments, features, segments, permissions, and audit logging, paired with a Next.js/React/TypeScript frontend (frontend/web). A dedicated edge_api service handles high-throughput, low-latency flag evaluation separately from the core management API, and integrations/ isolates third-party analytics wiring (Datadog, Segment, Amplitude, Rudderstack) from core flag logic. The separation of concerns is clear, though organisation-level subscription and licensing logic is somewhat entangled with core organisation models.

Tech Stack The backend runs Django 5 with Django REST Framework on Python, deployed via Docker Compose (with a pgpool variant for connection pooling at scale) and supporting PostgreSQL. The frontend uses Next.js and React with TypeScript, bundled with rspack, and tested with Jest and Playwright for end-to-end and visual regression coverage. CI is split across dedicated GitHub Actions workflows for API and frontend, including ECS deployment pipelines and Chromatic visual diffing.

Code Quality The API carries an extensive unit and integration test suite (300+ test files) alongside a smaller but present frontend test suite, both wired into pull-request CI. Python code uses type hints in core modules, and the frontend is fully TypeScript. Documentation is comprehensive, with a dedicated docs/ site and a CONTRIBUTING guide, reflecting a mature open-source contribution process.

What Makes It Unique Flagsmith combines feature flags, remote config, and segment-based multivariate testing in a single open-core platform, with enterprise-grade SSO (SAML, Okta, ADFS) and SCIM provisioning built into the same codebase rather than split into a separate closed product. The dedicated edge evaluation service is a deliberate architectural choice for teams needing flag reads at scale, though the core flagging model itself follows established patterns from the feature-flag space.

Self-Hosting

Licensing Model BSD-3-Clause licensed for the majority of the platform; a small number of repositories are MIT licensed. Core feature flagging, remote config, and self-hosted deployment work without any license key.

Self-Hosting Restrictions

• Enterprise-tier governance and management features require a valid Flagsmith Enterprise license
• License and subscription state are checked via is_enterprise()/has_enterprise_subscription() in the organisation model, gating specific organisation-level behavior

Enterprise Features

• SAML, Okta, and Microsoft ADFS single sign-on
• SCIM-based user and group provisioning
• Extended audit logging and organisation administration controls

Cloud vs Self-Hosted The hosted SaaS at flagsmith.com offers the same Enterprise tier as a paid upgrade; self-hosters need a purchased Enterprise license key to unlock the same SSO/SCIM/governance features.

License Key Required Yes, for Enterprise-tier features only — core flag, remote-config, and A/B-testing functionality is fully open and requires no key.