Auto‑clear storage vs manual cy.clearLocalStorage() for Cypress memory‑leak mitigation

Short answer

If you're on Cypress 12 or later, you probably don't need any of the three options you're weighing — and you don't need a new auto-clear flag either. Since v12, testIsolation defaults to true, which means Cypress already clears localStorage, sessionStorage, and cookies before every test. The premise that "Cypress does not clear storage automatically" describes pre-v12 behavior (or a config where testIsolation was explicitly disabled). The manual afterEach(() => cy.clearLocalStorage()) hook and the about:blank navigation trick were workarounds for that older behavior.

Comparing your three options

Built-in isolation (Cypress 12+)

This is the fastest and most predictable option. The reset happens at the browser level between tests, not as a Cypress command, so it doesn't add to your command queue, doesn't appear in the log, and clears cookies and both storage types together. There is nothing to configure unless someone turned it off.

Manual cy.clearLocalStorage() in afterEach

Under default isolation this is redundant — each call is a real command that visits the origin and executes, so across hundreds of tests the overhead is small but measurable, and it buys you nothing the framework doesn't already do. Keep it only if testIsolation is false or you're pinned to Cypress < 12. One caveat: cy.clearLocalStorage() with no arguments clears all keys, so if any test seeds storage in beforeEach, ordering mistakes will break it.

Navigating to about:blank in beforeEach

This was the standard pre-v12 trick. It clears origin-scoped storage, but it forces a page reload, doesn't cleanly reset cookies, and can destroy authentication state mid-suite. Compared with the built-in reset it is slower and less predictable. There is no reason to prefer it on a current Cypress version.

A note on the memory-leak framing

Storage accumulation is rarely the real driver of memory growth in long Cypress runs. The command log, DOM snapshots, and screenshots retained per test typically dominate browser memory pressure. Clearing localStorage alone is unlikely to fix an out-of-memory crash — if that's your actual symptom, look at run length, numTestsKeptInMemory, and screenshot/video settings instead.

Preserving cookies and auth state

For tests that rely on a persisted SSO session, the intended mechanism is cy.session(). It caches and restores authentication state quickly while storage isolation still prevents cross-test leakage — so you get isolation and fast login without disabling testIsolation globally.

Iframes

Storage belongs to origins, not frames. A same-origin iframe shares the parent origin's storage and is covered by the same isolation reset. Cross-origin iframe storage isn't reachable via cy.clearLocalStorage() at all, so no manual strategy fully addresses it either.

How to verify your situation

1. Check your Cypress version in package.json and search cypress.config.js/cypress.config.ts for testIsolation. On v12+ with no override, storage is already cleared between tests.
2. Write two sequential tests: the first sets a localStorage key, the second asserts it's absent — with no manual clearing. If it passes, built-in isolation is working and you can delete the afterEach hook.
3. If you want to justify the deletion with numbers, time the suite with and without the hook.
4. For cookie-dependent flows, confirm cy.session() restores auth across tests while isolation stays enabled.

One diagnostic detail would change this recommendation: your Cypress version. If you're on v11 or earlier and can't upgrade, then the manual afterEach clear is the better of your two workarounds — it's more explicit and less disruptive to cookies than the about:blank reload.