For independent Playwright runs, create a fresh BrowserContext for each test or session, create its pages inside that context, and close it when the work is done. A context separates browser-side state such as cookies and web storage; it does not isolate shared accounts, database records, files, or other server-side resources.
What browser-session isolation means in Playwright
Playwright describes its test environments this way: “Tests written with Playwright execute in isolated clean-slate environments called browser contexts.” Playwright’s browser-context documentation explains that contexts give tests independent browser sessions.
A BrowserContext is the practical boundary for browser-side session state. Pages and popups created in a context belong to that session. Use multiple pages in one context when they should share identity and state; use separate contexts when they must not.
Playwright Test creates a new context for each test by default. If you control the browser directly, create contexts explicitly. The guidance here is specific to Playwright; other automation frameworks may define isolation differently. Playwright’s living documentation and API reference can change, so check the docs for the version installed in your project: BrowserContext API reference.
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Create and close a fresh context for each independent run
For direct browser automation, launch a browser, create a non-persistent context, make a page inside it, run the task, and close the context. Non-persistent contexts do not write browsing data to disk.
JavaScript example
const { chromium } = require('playwright');
(async () => {
const browser = await chromium.launch();
try {
const context = await browser.newContext();
try {
const page = await context.newPage();
await page.goto('https://example.com');
console.log(await page.title());
} finally {
await context.close();
}
} finally {
await browser.close();
}
})();Closing the context at the end prevents a later run from depending on its live browser state. If a task intentionally uses several tabs as one signed-in user, create those pages from the same context rather than separate contexts.
Playwright Test
With Playwright Test, use the runner’s per-test context or page fixture rather than sharing a page or context through module-level variables. The runner supplies isolated contexts by default. Keep tests independent of execution order as well as browser state.
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Reuse authentication state without sharing a live session
Logging in for every test can be inconvenient. Playwright supports saving browser storage state after authentication and loading that snapshot into a new context. This transfers selected state intentionally; it does not mean tests should depend on another test’s live context.
- Run an authentication setup step and sign in.
- Save the state with
await context.storageState({ path: 'playwright/.auth/user.json' }). - Create a separate context for a test with
const context = await browser.newContext({ storageState: 'playwright/.auth/user.json' }). - Close the context when the test finishes.
Check the application’s actual authentication mechanism. Playwright’s storage-state functionality covers cookies and local storage, with documented support/options for IndexedDB and WebAuthn credential handling. It does not directly persist session storage. If the application relies on session storage, explicitly save and restore it using an initialization script or application-specific setup. See Playwright’s authentication guidance.
Protect the state file
A storage-state file can contain cookies and headers capable of impersonating an account. Treat it like a credential: do not commit it, restrict access, and keep its directory in .gitignore. Playwright’s authentication guide recommends an authentication-state directory in the ignore file.
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Make parallel tests safe beyond the browser
Separate contexts prevent browser-side state carryover, but they cannot stop two tests from changing the same server-side object. Parallel runs need unique or worker-scoped external resources too. Playwright’s parallelism guidance is relevant when designing those fixtures.
- Give tests unique record identifiers, or assign worker-specific accounts when tests modify shared data.
- Write each test’s downloads, screenshots, and reports to unique output paths.
- Avoid mutable module-level state and test-order dependencies.
- Use cleanup or disposable test data where the application permits it.
A useful diagnostic distinction: if a test sees another run’s cookie or local storage, check context reuse; if it sees another run’s changed record or overwritten file, isolate the backend fixture or output path.
Use a persistent profile only when continuity is required
A persistent context stores browser data in a user-data directory so a later run can continue with that profile. It is a different choice from a disposable context: it retains disk-backed browser state, and it is the only context for that browser instance.
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Do not start concurrent browser instances against the same user-data directory. Playwright also warns that automating Chrome’s default user profile is unsupported; use a separate directory for automation. See the BrowserType API reference.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Stabilize the rest of the test environment
Session isolation is necessary but not sufficient for reliable outcomes. For visual regression, Playwright recommends keeping operating-system and browser versions consistent. For interactions, prefer resilient locators tied to user-facing labels or roles; Playwright locators auto-wait and retry relevant actionability checks. See Playwright’s best practices.
The official material supports these qualitative reliability practices, but does not establish numerical speed, memory, or failure-rate comparisons between isolation strategies. Choose based on state lifetime, deliberate sharing needs, concurrency, and credential handling rather than an assumed performance advantage.
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Troubleshoot common isolation failures
A test unexpectedly appears signed in
Check whether the test reuses a context or loads a storage-state file. Use a fresh context without seeded state when a clean identity is required. If state reuse is intentional, verify the snapshot is the one the test expects.
Authentication disappears after loading a state file
Confirm which storage mechanism the app uses. A storage-state snapshot does not directly preserve session storage; restore that separately if required. Also verify that the setup step saved state after authentication completed.
Parallel tests change each other’s results
Inspect shared server-side accounts, records, files, and module-level variables. Give mutable fixtures and output paths unique or worker-specific names; separate browser contexts cannot make shared external resources independent.
A persistent launch fails or behaves inconsistently
Ensure no other browser instance is using the same user-data directory, and do not automate Chrome’s default profile. Give automation its own profile directory.
Visual screenshots differ across runs
Keep operating-system and browser versions consistent, then check for shared application data and unstable locators. Isolation cannot make a changing backend or environment deterministic.
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