Can Clear-Site-Data Delete Browser-Local AI History on Sign-Out?

September 6, 2026

Yes—but only for supported browser data under the responding origin. Learn what the header clears, what it misses, and how to test AI logout safely.

Yes. A private AI app can use the Clear-Site-Data response header to ask a supporting browser to delete browser-local chat history when you sign out—if that history is stored under the responding origin and the logout response includes the quoted "storage" directive. The header can also clear cookies and caches, but those are separate directives with different scope.

That makes Clear-Site-Data a useful privacy control, not a universal eraser. It does not delete server records, downloads, exports, browser backups, extension storage, another profile's data, or copies held under a different origin. It also does not replace server-side session invalidation.

The practical rule is: choose the intended data categories, send the header from the correct HTTPS origin, invalidate the session on the server, and prove the result with a harmless canary in every supported browser.

Research cutoff: September 6, 2026 (America/Chicago). Browser support and directive behavior can change. Test the exact browsers, versions, origins, and storage mechanisms your application supports.

The Short Answer

For an AI app at https://chat.example.com, a logout response could include:

Clear-Site-Data: "cookies", "storage", "cache", "executionContexts"

According to MDN's current Clear-Site-Data reference, the directives mean different things:

Every directive must use quoted-string syntax. Clear-Site-Data: storage is invalid; Clear-Site-Data: "storage" is the valid form.

What Is Confirmed

The header was designed for logout and local-data cleanup

The W3C Clear Site Data specification describes an imperative mechanism that lets a site instruct a browser to clear locally stored data related to a host. Its first sign-out example uses a CSRF-protected logout request and returns all four core directives: cache, cookies, storage, and execution contexts.

This is stronger than JavaScript that only calls localStorage.clear(). A modern AI web app may use several browser stores: IndexedDB for messages, Web Storage for preferences, the Cache API for offline resources, service workers for application behavior, and cookies for authentication. One JavaScript call does not cover all of them.

"storage" reaches the common browser-local AI history stores

MDN says "storage" covers localStorage, sessionStorage, IndexedDB, service-worker registrations, and other origin storage. That makes it the directive most directly connected to browser-local AI conversation history.

The exact result still depends on the app's architecture. A visible conversation list might be in IndexedDB while uploaded-file references live in a separate store. A desktop wrapper or browser extension may use an entirely different storage container. The header can clear only data inside the categories and scope the browser associates with the response.

Storage scope and cookie scope are not identical

The "storage" operation is origin-scoped. In web security terms, an origin includes the scheme, host, and port. Data for https://chat.example.com is therefore distinct from data for https://files.example.com or http://chat.example.com.

The "cookies" directive is broader in a different way: MDN says it affects the registered domain and its subdomains. A logout design that combines cookies and storage must account for that asymmetry. The response may remove cookies used across several subdomains while clearing storage only for the responding origin.

That is why a header sent from one origin cannot prove that browser-local chat data under every related origin was removed.

The header requires HTTPS

MDN documents Clear-Site-Data as a secure-context feature. An application should send it over HTTPS from the origin whose data it intends to clear.

For developers, this is another reason to test production-like environments. A local or misconfigured HTTP test can behave differently from the final HTTPS deployment, and a passing JavaScript-only cleanup test does not prove that the production response header is present.

Logout still needs server-side invalidation

OWASP's Session Management Cheat Sheet says an application must actively invalidate the server-side session when the user logs out. Expiring a browser cookie is not enough if the old session identifier remains usable at the server.

Clear-Site-Data works on browser-held state. It cannot reach into an application's session database, revoke an API token stored elsewhere, end a federated identity session, or cancel a refresh token at another service. A complete logout flow therefore has at least two independent jobs:

1. reject future use of the old authenticated session on the server; and
2. remove the intended browser-side records.

OWASP's current logout testing guidance recommends verifying that old session state cannot be reused after logout. That test belongs beside—not behind—the local-storage test.

What Is Still Unclear

The presence of a Clear-Site-Data header does not reveal whether a particular AI app's deletion promise is complete. Important implementation questions remain:

• Which origin owns the conversation database?
• Are chat messages in IndexedDB, Web Storage, the Cache API, an extension, a desktop wrapper, or several stores?
• Does an embedded iframe hold data under a third-party origin?
• Does another app subdomain store uploads, thumbnails, search results, or generated media?
• Do open tabs reload before they can rewrite a remembered in-memory copy?
• Does the app intentionally preserve some local history across logout?
• Does the browser version support every directive the response sends?
• Are service workers, offline caches, and persistent files included in the tested path?
• Can a different browser profile, device backup, browser sync feature, or exported file restore the record?
• What provider-side, billing, abuse-prevention, security, or legally retained records follow separate policies?

The only reliable answer comes from current documentation plus a controlled test of the exact product and browser.

What The Header Does Not Delete

Clear-Site-Data is powerful precisely because it is scoped. It does not establish deletion of:

• normal server-side chat history or account records;
• AI-provider processing records;
• billing, security, audit, or abuse-prevention records;
• files downloaded outside the browser's site-data container;
• screenshots, clipboard contents, printouts, or copied text;
• browser-profile backups, system images, or cloud-drive versions;
• data in a different browser or browser profile;
• browser-extension storage unless that extension separately responds to the logout event;
• native-app or desktop-wrapper databases;
• another origin's localStorage or IndexedDB; or
• a recipient's copy of a shared conversation.

The W3C specification also distinguishes logical deletion from forensic erasure of disk remnants. A browser can make stored data unavailable through its normal interfaces without proving that no recoverable byte exists anywhere on the device. Do not turn a web header into a device-forensics claim.

Should Every AI App Clear All Local History On Sign-Out?

Not necessarily. The correct choice depends on the product promise.

A privacy-sensitive app used on shared computers may make “sign out and clear this device” the safest default. A browser-local notebook may intentionally preserve local history so a returning user can continue without maintaining a normal server-side archive. Clearing all storage can also remove drafts, settings, offline documents, accessibility preferences, and unfinished work.

The better design is explicit:

• Sign out: invalidate authentication, with clear language about whether local history remains.
• Sign out and clear this browser: invalidate authentication and remove the intended local records.
• Delete one chat: remove the selected conversation without destroying unrelated local state.
• Clear all local history: remove the app's conversation data for the current origin and profile.
• Delete account: start the provider-side deletion process under the product's documented policy.

Those labels describe different outcomes. Combining them behind one vague logout icon creates avoidable privacy surprises.

A Safer Implementation Pattern

Use this five-part pattern when logout is supposed to remove browser-local AI history.

1. Map every storage location

Inventory cookies, localStorage, sessionStorage, IndexedDB databases, Cache API entries, service workers, object URLs, downloads, extension stores, and other origins. Do this from code and browser developer tools rather than from product assumptions.

2. Decide what logout is allowed to destroy

Some local records may be account-specific and sensitive; others may be device-wide preferences that should survive. If selective deletion is required, application code may be safer than clearing every origin store. If the product promises a complete browser cleanup, test that promise across every storage path.

3. Invalidate the authenticated session first

Use a CSRF-protected logout request. Revoke or invalidate the server-side session and expire its browser credential. Confirm that replaying the old credential fails.

4. Return the least-destructive complete header

Send the directives that match the documented outcome. Use "storage" when browser-local history must go, "cookies" when relevant browser credentials must go, "cache" when sensitive responses must not remain cached, and "executionContexts" when other open tabs must reload.

Avoid using "*" merely because it is shorter. Broad clearing can destroy unrelated local work and makes it harder to explain the boundary.

5. Verify behavior, not just syntax

Confirm the actual response in the network inspector. Then prove that the data is gone through the application's user-visible paths and browser storage tools.

The CLEAR Test For AI Logout

Use a harmless synthetic phrase such as PURPLE-LANTERN-6402, never a real secret.

C — Create A Canary

Put the unique phrase in a disposable local conversation, draft, and any relevant upload label. Record which origin and browser profile hold it.

L — Log Out And Capture The Response

Use the intended logout control. Confirm that the response is HTTPS, contains correctly quoted directives, and comes from the origin whose storage should be removed.

E — Examine Every Store

Inspect IndexedDB, Local Storage, Session Storage, Cache Storage, cookies, and service-worker registrations. Check related subdomains and embedded origins separately.

A — Attempt Session Reuse

Try the authorized security test for your environment: replay the old session credential or use the browser's Back button and another open tab. The server must require authentication, and stale pages must not regain protected access.

R — Reopen And Retest

Close and reopen the site in the same profile. Search for the canary. Repeat on every supported desktop and mobile browser, then test another tab, an interrupted request, an offline state, and a failed logout response.

A passing CLEAR test shows that the tested product path behaved as intended. It does not prove deletion from backups, another device, provider systems, or untested browser versions.

Common Failure Modes

The app clears cookies but leaves IndexedDB

The user reaches the login screen, but the conversation database remains on the device. A later sign-in—or application code running before authentication—can make it visible again.

The app clears storage but leaves the server session alive

The local conversation disappears, but a stolen or copied session credential still works. This is a session-security failure, even though the device looks clean.

The header comes from the wrong origin

The login service at accounts.example.com sends "storage", while the chat database lives at chat.example.com. The logout succeeds and the wrong storage bucket is cleared.

Another tab repopulates state

An already-open tab still holds conversation data in memory or runs older application code. The "executionContexts" directive is designed to reload contexts for the origin, but developers must test real multi-tab behavior and failure recovery.

The UI hides the chat without deleting its data

An empty sidebar can be caused by a cleared index while the message records remain. Verify the underlying stores and attempt the same search or recovery paths that previously surfaced the canary.

Where OpenVeil Fits

OpenVeil is an 18+ hosted, privacy-focused AI workspace. Normal OpenVeil chat history is kept in the user's browser, and OpenVeil does not maintain a server-side chat-history record for normal private chat sessions.

That makes local lifecycle controls consequential: browser-local history follows the browser origin and profile, not merely the account's sign-in state. As the guide to signing out of a private AI app explains, reaching a login screen does not by itself prove that local conversations were deleted. The broader guide to browser-local AI chat history explains why local history and active hosted processing are separate boundaries. If data was already cleared, the browser-local chat recovery guide explains why recovery normally depends on another surviving copy.

OpenVeil does not use prompts, uploaded files, images, audio, selected local-history context, or AI outputs to train foundation models. It is still a hosted service: active chat, search, upload, voice, image, and video requests may be processed by OpenVeil and the necessary providers for the selected feature.

OpenVeil is not fully offline, anonymous, zero-log, HIPAA compliant, or a device-forensics service. A browser-side cleanup cannot delete copies held in other apps, profiles, downloads, backups, screenshots, recipient systems, or unrelated provider records. Review the OpenVeil privacy policy before using sensitive material.

Frequently Asked Questions

Does Clear-Site-Data: "storage" delete IndexedDB?

Yes, for the origin associated with the response in a supporting browser. MDN includes IndexedDB among the storage mechanisms covered by the "storage" directive. Test the exact browser and app because another origin, extension, profile, or backup is outside that scope.

Does the header delete localStorage and sessionStorage?

Yes, the "storage" directive covers both for the responding origin. Clearing only "cookies" does not request the same storage deletion.

Does "cookies" automatically clear browser-local AI chats?

Not if the chats are stored in IndexedDB, Web Storage, or another non-cookie store. Use the directive that matches the actual storage mechanism.

Can a logout response clear data for every subdomain?

Not uniformly. Cookie clearing can affect the registered domain and subdomains, while DOM storage is origin-scoped. A multi-origin app must handle and verify each origin deliberately.

Does Clear-Site-Data delete cloud chat history?

No. It is a browser-side mechanism. Provider-side history and other records require the product's own deletion controls and policies.

Is Clear-Site-Data supported everywhere?

MDN labels the feature widely available but notes that some parts have varying support. Treat compatibility tables as a starting point and test the browser versions your users actually run.

Should developers use "*" on every logout?

Usually not without a clear product reason. The wildcard requests all supported categories and may remove useful unrelated state. Selective, documented behavior is easier to test and explain.

How can a user tell whether an AI app sends the header?

Open browser developer tools, enable the Network panel, perform the logout, select the logout response, and inspect its response headers. Use a synthetic canary to confirm the result; the header's presence alone does not prove the entire product data lifecycle.

Bottom Line

The Clear-Site-Data header can delete browser-local AI history on sign-out when the app sends the quoted "storage" directive from the correct HTTPS origin and the browser supports it. It can also clear cookies, caches, and active execution contexts when those directives are included.

But it is not an account-deletion API, a server-session revocation system, a cross-origin eraser, or a forensic wipe. A trustworthy implementation maps every storage location, explains what logout will remove, invalidates the session on the server, uses the narrowest complete set of directives, and verifies the result with a harmless canary across supported browsers.

Sources

• MDN: Clear-Site-Data response header
• W3C: Clear Site Data specification
• OWASP: Session Management Cheat Sheet
• OWASP: Testing for Logout Functionality
• MDN: HTTP caching
• MDN: localStorage
• MDN: IndexedDB API