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The Delivery API runs at https://fly.feather.mupeni.dev. It is optimized for flag evaluation on the hot path: every evaluation is served from an in-memory cache with at most two cache reads on cold start. This API is used exclusively by the SDK. You do not need to call it directly.

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Endpoints

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How it differs from the Management API

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Auth

API key in Authorization: Bearer <key>. Session cookies are not accepted.
  • Server keys (sk_...) — evaluate any flag, including non-clientSafe ones.
  • Client keys (pk_...) — evaluate only flags with clientSafe: true.

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Cold start path

On the first request to a new worker instance, the runtime makes at most two cache reads:
  1. Resolve orgId + environmentId from the API key
  2. Load the full flag bundle for the environment
The bundle is cached in memory for 30 seconds. All subsequent evaluations within the same instance lifetime hit only the in-memory cache.

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Flag bundle

The flag bundle is a JSON object of flagKey → FlagConfig. It is updated automatically on every Management API config change and can be manually refreshed via Trigger Sync.

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Evaluation reasons

See Evaluation for the full list of reasons and how they’re produced.