Feature flag service for controlling feature visibility without redeploying code. Define flags with targeting rules and percentage-based rollouts, then evaluate them in Workers via a native binding or from any JavaScript runtime via the OpenFeature SDK.
| Need | Use Flagship? | Alternative |
|---|---|---|
| Feature toggles (on/off) | Yes | — |
| Gradual rollouts (percentage-based) | Yes | — |
| A/B testing with attribute targeting | Yes | — |
| Multi-variant configuration delivery | Yes | — |
| Environment-specific config (dev/staging/prod) | Consider | Wrangler environments, secrets |
| Static config that never changes | No | wrangler.jsonc vars |
| Per-request rate limiting | No | Rate Limiting rules |
- Apps — Top-level organizational unit. Maps to a project or service. Each account can have multiple apps.
- Flags — Named feature toggles with a key, variations, targeting rules, and enabled/disabled state.
- Variations — Possible values a flag returns. Types: boolean, string, number, JSON object. All variations on a flag must share the same type.
- Targeting rules — Sequential, priority-ordered conditions that determine which variation to serve. First match wins; no match returns the default.
- Evaluation context — Key-value attributes (
userId,country,plan, etc.) passed at evaluation time for rule matching and rollout bucketing. - Percentage rollouts — Gradually release to a fraction of users. Consistent hashing on a configurable attribute ensures sticky bucketing.
| Path | Runtime | Package | Latency | Auth |
|---|---|---|---|---|
Binding (env.FLAGS) |
Workers only | @cloudflare/workers-types |
Lowest (no HTTP) | Automatic via binding |
| OpenFeature SDK | Workers, Node.js, browser | @cloudflare/flagship + @openfeature/server-sdk or @openfeature/web-sdk |
HTTP per eval (server) or prefetch (client) | API token or binding passthrough |
Recommendation: Use the binding inside Workers. Use the SDK when running outside Workers or when you need OpenFeature vendor-neutrality.
| Task | Read |
|---|---|
| Set up Flagship in a Worker | configuration.md → api.md |
| Evaluate flags in code | configuration.md → patterns.md |
| Manage flags via REST API | api.md → patterns.md |
| Design targeting rules & rollouts | patterns.md → gotchas.md |
| Debug flag evaluation issues | gotchas.md → api.md |
REST API note: management endpoints use Cloudflare v4 envelopes (result, result_info, errors) and snake_case fields. The /evaluate endpoint is the exception: it is not enveloped and returns OpenFeature-style camelCase.
- api.md — REST API endpoints, binding methods, OpenFeature SDK, schemas
- configuration.md — Wrangler binding setup, SDK installation, TypeScript types
- patterns.md — Flag CRUD via API, targeting rules, rollouts, OpenFeature usage
- gotchas.md — Common errors, limits, anti-patterns, troubleshooting
- Flagship API reference — Source of truth for REST API paths, envelopes, and response fields
- ../workers/ — Workers runtime (Flagship runs inside Workers)
- ../kv/ — KV storage (Flagship uses KV infrastructure for flag delivery)
- ../wrangler/ — Wrangler CLI for deployment and config