VTDT0002: Vitest UI Server Unreachable

Message

Vitest UI server did not become reachable at {url} within {timeout}ms.

Cause

After spawning vitest --ui, the launcher polls the Vitest UI URL until it responds, then swaps the dock entry to an iframe embedding it. This diagnostic is thrown when the server does not answer within the timeout — usually because Vitest failed to start (a config error, a missing dependency, or the process exiting early).

Example

Launching the Vitest UI in a project whose vitest.config.ts throws during load, so the UI server never begins listening.

Fix

Open the Vitest UI terminal session in the Terminals dock and read its output for the underlying startup error, resolve it, then launch again.

Source

• packages/vitest/src/node/plugin.ts — onLaunch polls the spawned server with waitForServer() and throws this when it stays unreachable past the timeout.