vitest-dev/vitest · error · TypeError

The browser server was not initialized${project.name ? ` for

Error message

The browser server was not initialized${project.name ? ` for the "${project.name}" project` : ''}. This is a bug in Vitest. Please, open a new issue with reproduction.

What it means

Internal assertion in the browser pool: after project._initBrowserProvider() resolves, project.browser must be set. If it is still falsy, browser provider initialization silently failed to populate the server reference, which the framework treats as a bug rather than a recoverable state.

Source

Thrown at packages/vitest/src/node/pools/browser.ts:95

        testLocations: testLines,
        testIds,
        testNamePattern,
        testTagsFilter,
        fileTags: testFileTags.get(spec),
      })
      groupedFiles.set(project, files)
    }

    let isCancelled = false
    vitest.onCancel(() => {
      isCancelled = true
    })

    const initialisedPools = await Promise.all(Array.from(groupedFiles.entries(), async ([project, files]) => {
      await project._initBrowserProvider()

      if (!project.browser) {
        throw new TypeError(`The browser server was not initialized${project.name ? ` for the "${project.name}" project` : ''}. This is a bug in Vitest. Please, open a new issue with reproduction.`)
      }

      if (isCancelled) {
        return
      }

      debug?.('provider is ready for %s project', project.name)

      const pool = ensurePool(project)
      vitest.state.clearFiles(project, files.map(f => f.filepath))
      providers.add(project.browser!.provider)

      return {
        pool,
        provider: project.browser!.provider,
        runTests: () => pool.runTests(method, files),
      }
    }))

View on GitHub (pinned to d568f8ce37)

Solutions

1. Report as a Vitest bug with a minimal repro (config.browser configuration + provider).
2. Verify config.browser.provider is a supported value ('playwright', 'webdriverio') or a correctly implemented custom provider.
3. Ensure config.browser.enabled is true and the provider package is installed and importable.
4. Try a different built-in provider to isolate whether a custom provider is at fault.

// Confirm browser provider loads before delegating to the pool
const project = vitest.projects.find(p => p.config.browser.enabled)
await project._initBrowserProvider()
if (!project.browser) {
  throw new Error('Browser provider failed to initialize; check provider config/install')
}

try {
  await vitest.start()
} catch (e) {
  if (e.message.startsWith('The browser server was not initialized')) {
    console.error('Browser provider init failed. Verify config.browser.provider is installed.')
  }
  throw e
}

When it happens

Trigger: createBrowserPool -> runWorkspaceTests iterates groupedFiles per project, calls project._initBrowserProvider() at packages/vitest/src/node/pools/browser.ts:92, then checks project.browser at :94. If the provider init did not assign project.browser (a framework invariant), this throws.

Common situations: A custom browser provider that does not correctly initialize the server on the project; a regression in browser provider initialization across Vitest versions; browser.enabled in config but the provider failed to load and the error was swallowed before this assertion.

Related errors

• Orchestrator not found for session ${sessionId}. This is a b
• Unexpected empty queue
• The ${provider.name} provider does not support tracing.
• The ${context.provider.name} provider does not support traci
• provider ${context.provider.name} is not supported

AI-assisted analysis of vitest-dev/vitest@d568f8ce37 (2026-08-03). Data as JSON: /data/errors/f23d1b0662f3a124.json. Report an issue: GitHub.