The packages

@nice-code/error

Declare error domains once, then throw, catch, serialize, and narrow them with full type inference. Multi-ID errors, pattern matching, and safe transport across any boundary.

@nice-code/action

Wrap server functions as actions with typed input, output, and errors. Requesters on the client, resolvers on the server — no codegen.

@nice-code/common-errors

Shared error domains. Standard Schema validation errors and Hono middleware, ready to drop in.

Why nice-code

Serialization-first

Errors round-trip through JSON.stringify and come back as the same typed error — via toJsonObject() on the way out, castNiceError() on the way in.

Type-safe context

Each error ID declares its context shape. TypeScript narrows on .hasId() and .hasOneOfIds(), giving you typed context access with no casts.

Pattern matching built-in

handleWithSync and handleWithAsync route errors to the first matching case. forDomain, forId, forIds — no switch statements needed.

Works everywhere

Node, Bun, Deno, browsers, service workers, edge runtimes, Cloudflare Workers. No environment assumptions.

In thirty seconds

import { defineNiceError, err } from "@nice-code/error"

export const err_billing = defineNiceError({
  domain: "err_billing",
  schema: {
    payment_failed: err<{ reason: string }>({
      message: ({ reason }) => `Payment failed: ${reason}`,
      httpStatusCode: 402,
      context: { required: true },
    }),
    card_expired: err({ message: "Card has expired", httpStatusCode: 402 }),
  },
})

import { err_billing } from "./errors"

export async function charge(amount: number) {
  const result = await stripe.charge(amount)
  if (!result.ok) {
    throw err_billing.fromId("payment_failed", { reason: result.message })
  }
}

import { castNiceError, forDomain } from "@nice-code/error"
import { err_billing } from "./errors"

try {
  await charge(500)
} catch (e) {
  const error = castNiceError(e)
  error.handleWithSync([
    forDomain(err_billing, (h) => {
      if (h.hasId("payment_failed")) {
        showError(h.getContext("payment_failed").reason)
      }
    }),
  ])
}