vitest-dev/vitest · error · Error

Browser provider is not defined for the project "${child.pro

Error message

Browser provider is not defined for the project "${child.project.name}". This is a bug in Vitest. Please, open a new issue with a reproduction.

What it means

While generating the virtual `vitest/browser` context module, Vitest reads `child.config.browser.provider.name` to embed the provider name in the bundled client code. If that field is undefined, it indicates provider resolution never completed for this project — the message explicitly asks for a bug report because every browser project should have a resolved provider name by this point.

Source

Thrown at packages/browser/src/node/plugins/pluginContext.ts:50

  }
}

async function generateContextFile(
  this: Rollup.PluginContext,
  globalServer: ParentBrowserProject,
) {
  const commands = Object.keys(globalServer.commands)
  // The provider instance is initialized lazily when a page opens, so reading
  // `child.provider` here races and can be `undefined` before the first page is
  // opened. The provider name is uniform across a project's instances and is
  // already resolved on the config, so read it from there for this shared
  // (cached) context module. The instance is still used below for the
  // preview-only user-event import.
  const child = [...globalServer.children][0]
  const provider = child.provider
  const providerName = child.config.browser.provider?.name
  if (!providerName) {
    throw new Error(
      `Browser provider is not defined for the project "${child.project.name}". This is a bug in Vitest. Please, open a new issue with a reproduction.`,
    )
  }

  const commandsCode = commands
    .filter(command => !command.startsWith('__vitest'))
    .map((command) => {
      return `    ["${command}"]: (...args) => __vitest_browser_runner__.commands.triggerCommand("${command}", args),`
    })
    .join('\n')

  const userEventNonProviderImport = await getUserEventImport(
    provider,
    this.resolve.bind(this),
  )
  const distContextPath = slash(`/@fs/${resolve(__dirname, 'context.js')}`)

  return `

View on GitHub (pinned to d568f8ce37)

Solutions

1. Install the browser provider package: `pnpm add -D @vitest/browser-playwright` (or `webdriverio`).
2. Set `test.browser.provider` explicitly in the config (`'playwright'`, `'webdriverio'`, or `'preview'`).
3. Verify `@vitest/browser` and the provider package match the installed `vitest` version.
4. If config looks correct, follow the message and open a Vitest issue with a minimal reproduction.

Example fix

// before
export default defineConfig({
  test: { browser: { enabled: true, name: 'chromium' } },
})

// after
export default defineConfig({
  test: {
    browser: {
      enabled: true,
      name: 'chromium',
      provider: 'playwright',
    },
  },
})

import { existsSync } from 'node:fs'
import { resolve } from 'pathe'

function assertProviderConfigured(config: { browser?: { provider?: { name?: string } | string } }): void {
  const name = typeof config.browser?.provider === 'string'
    ? config.browser.provider
    : config.browser?.provider?.name
  if (!name) {
    throw new Error('test.browser.provider must be set (e.g. "playwright") before importing vitest/browser')
  }
}

const hasProviderName = (c: { browser?: { provider?: { name?: string } | string } }): boolean => {
  const p = c.browser?.provider
  return typeof p === 'string' ? !!p : !!p?.name
}

When it happens

Trigger: Loading `vitest/browser` (e.g. importing it in a test or via the orchestrator) for a project whose `browser.provider.name` is falsy — provider resolution failed silently, the provider package isn't installed, or config explicitly left provider undefined while enabling browser mode.

Common situations: Missing `@vitest/browser` or a provider package (`@vitest/browser-playwright`, `@vitest/browser-webdriverio`); custom provider that doesn't expose `name`; mismatched Vitest/`@vitest/browser` versions where the config shape changed; corruption during config merge.

Related errors

• vitest/browser can be imported only inside the Browser Mode.
• No codec found for type ${type}
• Unrecognized comparator ${comparator}
• `resolveOptions` has to be used in a test file
• Tester HTML file "${testerHtmlPath}" doesn't exist.

AI-assisted analysis of vitest-dev/vitest@d568f8ce37 (2026-08-03). Data as JSON: /data/errors/64e7976b17ddbade.json. Report an issue: GitHub.