Define type-safe RPC contracts with effect/unstable/rpc — Rpc.make payload/success/error/defect schemas, RpcSchema.Stream streaming responses, RpcGroup composition (add/merge/omit/prefix/annotate), and RpcMiddleware.Service definitions shared by client and server. Use when declaring or evolving RPC procedures, building a shared contract package, adding streaming endpoints, or defining auth/observability middleware types.
Consume typed RPC services with Effect's RpcClient — protocol layers (HTTP, WebSocket, TCP, worker, in-memory), RpcSerialization codecs, per-call and ambient headers, streaming calls, interruption, reconnection, and RpcClientError handling. Use when calling an RpcGroup from a client, wiring a client transport + serialization stack, debugging RPC transport failures or reconnects, or testing RPC consumers with RpcTest.
Serve RpcGroup contracts with Effect's RpcServer — handler layers (RpcGroup.toLayer/toLayerHandler), protocol layers (HTTP, WebSocket, TCP, stdio, worker), RpcSerialization, server middleware, streaming results, interruption and shutdown semantics, RpcTest. Use when implementing the server side of an Effect RPC API, mounting RPC on an HttpRouter or existing HTTP app, choosing a wire format, implementing RpcMiddleware, handling client aborts, or testing RPC handlers.
Make outgoing HTTP requests with Effect's HttpClient — HttpClientRequest builders, schema-decoded HttpClientResponse bodies, the HttpClientError taxonomy, retryTransient/rate limiting/cookies/redirects, streaming uploads and downloads, and FetchHttpClient/NodeHttpClient transport layers. Use when calling external REST/JSON APIs, uploading or downloading files and streams, adding retries/auth/tracing to outbound HTTP, or mocking HTTP responses in tests.
Build HTTP servers with effect/unstable/http — HttpRouter routes and middleware, HttpServerRequest schema decoding, HttpServerResponse constructors, multipart uploads, websocket upgrades, static files, NodeHttpServer/BunHttpServer layers, and in-memory web handlers. Use when serving raw HTTP routes, reading request bodies/cookies/uploads, writing server middleware, streaming responses, or testing handlers without a real port.
Build bidirectional socket transports with effect/unstable/socket — the Socket run/writer surface, WebSocket-backed sockets, TCP/Unix-domain clients via NodeSocket, SocketServer accept loops, channel adapters, the SocketError taxonomy, and reconnect patterns. Use when connecting to or serving raw TCP, Unix-domain, or WebSocket endpoints, framing socket bytes with Stream/Channel (NDJSON), building reconnecting socket clients, or providing socket transports to RPC/devtools layers.
Cache effectful lookups in memory with Cache and ScopedCache — capacity/LRU eviction, fixed or exit-aware TTL, deduplicated concurrent lookups, refresh/invalidation, and resource-owning entries with per-entry scopes. Use when memoizing effectful lookups by key, adding TTL caching to API or DB reads, deduplicating concurrent fetches of the same key, or caching values that own resources such as connections.
Fork, supervise, and interrupt Effect fibers with Effect.forkChild/forkScoped/forkIn/forkDetach, Fiber join/await/interrupt, uninterruptible regions, and the FiberHandle/FiberMap/FiberSet supervision collections. Use when running background work, cancelling or restarting tasks, implementing latest-wins or keyed workers, bridging Effect into callback APIs, or debugging interruption and fiber lifetime issues.