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Strict Origin Isolation Trial

tl;dr This page describes a desktop Canary-only field trial to study the effect of isolating pages by origin (as opposed to the current Site Isolation approach using sites) on Chrome's performance. The trial will be one week in duration, starting around May 23rd, 2019. Some pages, such as those that rely on setting document.domain to perform cross-origin scripting, may encounter issues during this trial.

Tracking Issue: “Evaluate feasibility of widespread origin isolation”


The Strict Origin Isolation Trial is a short-duration (one week) field trial designed to gather preliminary data about the performance impact of changing the granularity of isolation from site (protocol and eTLD+1) to origin (protocol, host, and port).

Strict Origin Isolation would improve security by ensuring different origins do not share a process with each other, but it poses a risk of increased resource usage. This study will allow us to study the expected impact on process count, memory usage, and other performance metrics if all origins were isolated, including potential performance benefits from increased parallelization.

However, this trial also poses a functional risk to web pages that script same-site but cross-origin frames, which is possible if the pages modify their document.domain values via JavaScript. Such cross-origin scripting will be disrupted if the documents are in different processes, resulting in JavaScript errors visible in the DevTools console and potentially broken page features.

Sample cross-origin scripting error: On a page with a subframe, where both execute document.domain = ‘’, and attempts something like top.document.body.innertext, the following error occurs:
VM118:1 Uncaught DOMException: Blocked a frame with origin "" from accessing a cross-origin frame. at <anonymous>:1:5

Because of this risk, we will limit this trial to a single week on only the Canary channel, to avoid disruptions to users of the Dev, Beta, and Stable channels. 50% of Canary channel users will be opted in to the Strict Origin Isolation mode, while the remaining 50% will act as a control group using Site Isolation. The trial will only affect Chrome versions 76.0.3791.0 and higher.

Trial Contact Information

During the trial, if you need further information, please reach out to:



Disabling the Trial

If you encounter issues during the trial, you can opt-out by running Chrome with --disable-features=StrictOriginIsolation, or changing the chrome://flags/#strict-origin-isolation flag from Default to Disabled.

Reporting Bugs

If you experience incorrect behaviour during the trial, first check the variations list in chrome://version to see if the variation for the trial (0x4c825337 or 1283609399), is present. If so, and if the issue goes away when disabling the trial (see above), please file a bug by clicking on this link.

To avoid impact from the trial (and otherwise improve security), web developers can avoid modifying document.domain to script cross-origin frames.


Determining the feasibility of increasing Chromium’s isolation granularity from sites to origins is important for improving security performance for our users. This trial is a first step to better understand the implications, before considering next steps.