# `server.import.forbidden`: server.ts imports something other than @playable/sim

A build check error in the area "server.ts rules". An error: the game cannot be published until it is fixed.

The build check runs on every game LobbyLab builds, and each problem it finds has a stable code, the exact message, the file and line when it names one, and a link to this page.

## What the check looks at

server.ts exports `rulebook` (`init`, `advance`, `project`, and `tick` for realtime games). It must be deterministic, so the check scans the code and its strings for APIs that are not allowed.

## How to fix it

Import only named imports from the sim kit (`import { v2, clamp } from "@playable/sim"`). Write other helpers yourself.

Use `context.random` for randomness and `context.logicalTimeMs` for time, import only named imports from the sim kit, and keep display text with words like "Date" or "global" in the client.

See also: [every error code](/docs/errors), [the API reference](/docs/api) and [the docs](/docs).