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A successful Next.js build does not guarantee that Playwright can launch a browser or run tests on Vercel. Output tracing selects files for deployment; it does not install browser binaries or operating-system libraries, execute your app, or prove that tests pass. To diagnose a failure, first identify where the browser is meant to run—CI, a deployed function, or another environment—then check that environment’s browser setup, traced files, and production behavior.
What Next.js file tracing does
During next build, Next.js uses @vercel/nft to statically analyze import, require, and filesystem usage, producing trace information about files a page may load at runtime. That helps determine which files to include in a deployment; it is not a Playwright test run or a browser setup process. See the Next.js 15 output configuration guide.
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Four things tracing will not do
1. Install Playwright’s browser binaries
Playwright needs browser binaries that match the installed Playwright version. Its browser setup documentation describes installing them with the Playwright CLI, for example npx playwright install. A trace that includes application files does not run that command. If a deployed function is supposed to launch a browser, establish how the matching binary is made available in that specific runtime.
2. Install operating-system dependencies
Browser binaries are not the same as their host operating-system libraries. Playwright documents a separate dependency command, npx playwright install-deps, including options for selected browsers. File tracing does not install these OS packages. Check whether the environment that actually launches the browser supports installing and using the required dependencies.
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3. Find every dynamically loaded file
Static analysis cannot reliably infer every path assembled or selected at runtime. Vercel notes that some files in node_modules may need explicit inclusion with Next.js’s outputFileTracingIncludes option. The Vercel function-files guidance and the Next.js output guide explain tracing includes and excludes. If files are missing, inspect the trace output and add the necessary paths using the configuration supported by your installed Next.js version.
4. Prove the deployed code can launch a browser or pass tests
Including files is a packaging step, not evidence that a function can execute a browser or that a test succeeds. Next.js recommends testing production code by building and starting the production server, then running npx playwright test. Playwright also documents triggering tests after a deployment succeeds and using the deployment URL as the test base URL. See the Next.js Playwright testing guide and Playwright CI guide.
Diagnose a Playwright failure on Vercel
- Identify where the browser launches. Determine whether tests run in CI, from an application route or function, or elsewhere. Browser binaries and system libraries must be available in the environment that executes the browser.
- Match the browser installation to Playwright. Check the installed Playwright version and use its CLI to install the corresponding browser binaries in the execution environment.
- Check operating-system dependencies there. Confirm that the target environment can provide the libraries Playwright requires; a complete trace does not supply them.
- Inspect the deployment trace. For required runtime files that static analysis misses, configure
outputFileTracingIncludesaccording to the Next.js version in the project and verify that the files are included. - Test production behavior separately. Build and start the production app and run Playwright against it, or run tests against the successful deployment URL. A build finishing successfully is not a browser-launch test.
Choose the right place to run the browser
The key implementation decision is whether Playwright is a test runner in CI or a browser launched by deployed application code. These are different execution paths: a CI test job needs its browser setup in CI, while a function that launches a browser needs compatible binaries, OS dependencies, and runtime files in that function’s environment. The cited documentation describes testing a production server and testing a successful deployment; it does not establish one Vercel configuration that guarantees browser execution across every framework and runtime setup.
Likewise, there is no universal function-size limit or runtime recipe established here for all Vercel deployments. Check the current constraints and supported installation model for the particular runtime and deployment configuration rather than assuming a trace makes an otherwise unsupported browser setup work.
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