Introduction

nice-code is a collection of TypeScript libraries that share a single goal: keep your types intact at every boundary your program crosses — the network, the worker, the storage layer, the catch block.

The packages

Package	What it does
@nice-code/action	Transport-agnostic, bi-directional action system with full inference. The headline.
@nice-code/error	Typed, serializable errors with domain hierarchies and pattern matching.
@nice-code/state	Immer-backed state container with fine-grained selectors and reactions.
@nice-code/common-errors	Standard Schema validation errors + Hono middleware.
@nice-code/util	Typed storage adapters and WebCrypto utilities.

Start with @nice-code/action — it’s the centre of gravity. The rest compose around it: actions declare the errors they throw using error domains, secure channels use the crypto link from util, validation failures surface as common-errors. But each one stands on its own.

How they fit together

// An action declares its input, output, AND the errors it can throw —
// all in one shared definition both client and server import.
export const userDomain = appRoot.createChildDomain({
  domain: "user",
  actions: {
    getUser: actionSchema()
      .input({ schema: v.object({ userId: v.string() }) })
      .output({ schema: v.object({ id: v.string(), name: v.string() }) })
      .throws(err_user, ["not_found"]),   // ← @nice-code/error domain
  },
});

// Call it from anywhere. Output is typed; thrown errors are typed and narrowable.
const user = await userDomain.action.getUser
  .request({ userId: "u_1" })
  .runToOutput();

What nice-code is not

• Not a validator. Bring Valibot, Zod, or any Standard Schema library for boundary validation.
• Not an HTTP framework. Actions ride carriers (WebSocket, HTTP, in-memory, WebRTC) and plug into Hono, Workers, Node, Bun, Durable Objects.
• Not magic. Each library is small, readable, and dependency-light.

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