To debug Playwright and Puppeteer tests, first isolate the failing test, then collect evidence from the part of the system that may be failing: the test runner, page JavaScript, browser process, or CI environment. In Playwright, use Inspector or UI Mode for interactive diagnosis and capture traces for failures, especially in CI. In Puppeteer, make execution visible, forward page-console messages, and choose browser DevTools, Node’s inspector, or process logs based on where the suspected code runs.
Start by narrowing the failure
Run the smallest test scope that still reproduces the problem. A smaller run cuts unrelated output and makes it easier to see whether the failure is repeatable. If the issue may depend on a browser, retain the relevant project selection rather than silently changing the test environment.
Playwright: run one test, file, or project
The Playwright CLI accepts a test file, a line number, and a project selection. For example:
npx playwright test example.spec.ts:10 --project=chromiumUse the test file or line selection to target the failure; add --project when you need to isolate or compare configured browser projects. See the Playwright command-line reference for current selection syntax and options.
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Puppeteer: reduce the script to the failing path
Puppeteer is commonly used from a Node.js script rather than Playwright Test’s runner. Temporarily remove unrelated navigation and interactions, keeping the failing sequence and the same launch options. This helps distinguish a timing or page-state issue from setup or teardown behavior.
Make the browser interaction observable
Playwright Inspector
Run the failing test with debug mode to open a headed browser and the Playwright Inspector:
npx playwright test --debug
npx playwright test example.spec.ts --debug
npx playwright test example.spec.ts:10 --debugIn the Inspector, step through actions, inspect actionability information, and use the locator picker or live editing to check the target. A page.pause() call can stop the test at a chosen point for inspection. This is useful for seeing what the test is about to do, but a successful manual step-through does not by itself prove why an unattended run failed. Details are in Playwright’s debugging guide.
Playwright UI Mode
For a broader view of a run, launch UI Mode:
npx playwright test --uiUI Mode lets you walk through test steps and inspect errors, logs, network requests, DOM snapshots, and locators. It can provide more context than a terminal stack trace alone. The running and debugging tests guide documents the workflow.
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Puppeteer headed mode and slow motion
For Puppeteer, a headed browser and a short delay between operations can make a fast interaction sequence easier to observe:
const browser = await puppeteer.launch({ headless: false, slowMo: 250 });
const page = await browser.newPage();
page.on('console', msg => console.log('PAGE LOG:', msg.text()));Attach the console listener before the actions you want to diagnose. Headed mode and slowMo help expose unexpected page state or ordering; they are observation aids, not proof of a root cause. Puppeteer’s debugging guide covers these methods.
Check whether the locator or page state is wrong
Playwright actionability
When a click or other action stalls, inspect the locator’s match count and the Inspector’s actionability log. Determine whether the target was visible, enabled, stable, and ready when the test acted. A locator that matches nothing, matches multiple elements, or remains blocked by an overlay points to a different fix than a click that completed but produced the wrong page state.
Puppeteer locator waits and selector methods
Puppeteer’s locator API waits for elements and checks action preconditions. Do not assume that lower-level selector methods have identical waiting or retry behavior. Check which API the test uses and whether its documented behavior matches the timing the test needs. See Puppeteer’s page interactions guide.
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Collect evidence that matches the failure
Playwright traces
A Playwright trace provides an action timeline and related browser evidence, including snapshots, network activity, and logs. For failures that appear in CI, traces can show what happened in the run that failed rather than relying on a local reproduction. The Playwright best-practices guidance recommends traces for CI failures and warns that recording traces for every test can add substantial overhead.
For Playwright Test, configure trace collection through the test runner when you need test context and assertions. The lower-level context tracing API does not record test assertions, so it is not a like-for-like replacement for a test-runner trace. Open a trace with:
npx playwright show-trace trace.zipSee Playwright best practices and the Tracing API reference for configuration details and trade-offs.
Puppeteer browser traces and console output
Puppeteer can record a browser trace for inspection in Chrome DevTools or a timeline viewer:
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await page.tracing.start({ path: 'trace.json' });
// Run the interactions you need to investigate.
await page.tracing.stop();This is browser/timeline evidence, not the same artifact as a Playwright Test trace with runner context. For Puppeteer tracing options, see the Tracing class reference.
To expose page console messages in Node, register page.on('console', ...) before the suspect interaction, as in the earlier snippet. A screenshot can show a page at one instant, but it cannot by itself reconstruct the sequence of actions, requests, and state changes that led there.
Debug the correct execution context in Puppeteer
Puppeteer failures can originate in Node.js test code, JavaScript running in the page, or the browser process. Select the debugger or logging method for the suspected layer instead of treating all browser-related errors as page errors.
Node.js script or test code
Put a debugger statement in the Node-side script and launch Node with --inspect-brk to pause for inspection. This targets the test’s Node execution, not JavaScript inside the page.
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Code running in the page
Launch Puppeteer with devtools: true and put a debugger statement inside the callback passed to page.evaluate. That lets browser DevTools pause page-side execution where the suspect code runs.
Browser launch or protocol behavior
Use dumpio: true in the launch options to forward browser-process output. For lower-level Puppeteer logging, the debugging guide documents NODE_DEBUG="puppeteer:*". Treat protocol debug output as potentially sensitive: it may include information that should not be shared publicly. Consult Puppeteer’s debugging guide before collecting or publishing logs.
Handle failures that occur only in CI
A CI-only failure is a reproduction and evidence problem until you have comparable runs. Capture Playwright traces on failure rather than tracing every test by default; the latter carries a performance cost. A common failure-focused policy is to retain a trace on the first retry of a failed test, then inspect the trace for the action timeline, snapshots, requests, and logs.
Compare the failing CI run with the local run across the browser project, test configuration, environment, and logs. A local headed run that passes does not establish why CI failed. If you run headed tests on Linux in CI, Playwright’s CI documentation notes that Xvfb is required. See Playwright’s continuous integration guidance.
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These commands add evidence without changing the basic test flow:
# Playwright API-level logging
DEBUG=pw:api npx playwright test
# Playwright browser launch logging
DEBUG=pw:browser npx playwright testUse API logging when you need to see Playwright operations and browser logging when investigating launch-related behavior. Keep debug logs private if they may contain sensitive page or environment details.
Troubleshoot common symptoms
| Symptom | What to inspect | Next step |
|---|---|---|
| Playwright action times out | Inspector actionability details, locator match count, visibility, enabled state, stability, and overlays. | Correct the locator or page precondition; use a pause or UI Mode to inspect the state at the failing action. |
| Playwright passes locally but fails in CI | Failure trace, browser project, configuration, environment, and CI logs. | Collect traces for failures or retries and compare the actual CI run with the local run. Do not infer a cause from local headed success alone. |
| Puppeteer click appears to run before the target is ready | Whether the code uses a locator or a lower-level selector method, and the API’s documented waiting behavior. | Use an interaction API whose wait and preconditions fit the operation, or explicitly wait for the required page state. |
| Page error is missing from Node output | Whether a page-console listener was attached before the interaction and whether the fault is in page or Node code. | Forward page console messages; use browser DevTools for page execution or Node’s inspector for script execution. |
| Browser launch or protocol failure is unclear | Browser-process output and Puppeteer debug logs. | Try dumpio: true or documented protocol logging, handling collected output as potentially sensitive. |
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