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 serves the app, then swaps the dock entry to an iframe embedding it. Vitest 5 serves the UI only with the API token it prints on startup (UI started at …?token=…), so the launcher reads that token from the session output and polls the tokenized URL; Vitest's 403 auth page does not count as ready. This diagnostic is thrown when the UI is not served within the timeout — usually because Vitest failed to start (a config error, a missing dependency, or the process exiting early), or because the UI started at line never appeared in its output.

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 — serve.onReady polls the spawned server with waitForVitestUi() (from ui-url.ts) and throws this when the UI is not served past the timeout.