#CrossOriginStorage
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tomayac.com
If you're interested in the Cross-Origin Storage API, I just created a new Bluesky feed, check it out and pin it if you like it: bsky.app/profile/did:... #CrossOriginStorage
August 5, 2026 at 9:28 AM
tomayac.com
😎 Chromium (personal fork) passing all Web Platform Tests of the #CrossOriginStorage API.

* WIP CL: chromium-review.googlesource.com/c/chromium/s...
* Runnable binary: github.com/tomayac/Chro... (Linux x86_64)
Chromium on Linux x86_64 running 30 Web Platform Tests of the Cross-Origin Storage API. All tests pass.
August 16, 2026 at 9:53 AM
tomayac.com
I was on the @shoptalkshow.com with @chriscoyier.net and @davatron5000.bsky.social to chat about the #CrossOriginStorage API, see the quoted skeet ⤵️. If you bookmark just one link after the show, make it github.com/tomayac/awes....
September 14, 2026 at 1:48 PM
tomayac.com
Cross-Origin Storage API: Stop Downloading Twice: dev.to/morellodev/c.... A great overview of our proposal for the #CrossOriginStorage API by Dennis Morello. 👏
Cross-Origin Storage API: Stop Downloading Twice
The Cross-Origin Storage API lets sites share one cached copy of a file (a JS library, font, or AI model) across origins by SHA-256 hash. Here's how it works.
dev.to
July 22, 2026 at 7:17 AM
tomayac.com
🤩 It's happening!!1! I just sent the "Intent to Prototype" email for the #CrossOriginStorage API: groups.google.com/a/chromium.o.... If you want to stay in the loop, star the ☂️ umbrella Chromium bug crbug.com/547587764 (and the subtask bugs: crbug.com/547587764/de...).
Intent to Prototype: Cross-Origin Storage
groups.google.com
August 18, 2026 at 4:02 PM
tomayac.com
Look, ma, that's WebKit 🧭 passing all Web Platform Tests for #CrossOriginStorage. And you can try it: github.com/tomayac/WebK... (personal fork)! That's now four prototype implementations of the API in four different browsers: github.com/tomayac/awes... (all of them with releases you can run).
WebKit mini browser showing the passing test suite for the Cross-Origin Storage API: 30 passing tests.
August 14, 2026 at 10:33 AM
tomayac.com
More #CrossOriginStorage API updates: filed HTML issues (CSS already existed) toward better integration in the platform:

* Add `crossoriginstorage` attribute to `` and `
tomayac.com
Started an Awesome Cross-Origin Storage list: github.com/tomayac/awes... . Transformers.js, WebLLM, wllama, Flutter, Emscripten, Nuxt and Vite plugins, and a bunch of demos… #Awesome #CrossOriginStorage
GitHub - tomayac/awesome-cross-origin-storage: A curated list of resources for the Cross-Origin Storage (COS) API
A curated list of resources for the Cross-Origin Storage (COS) API - tomayac/awesome-cross-origin-storage
github.com
July 4, 2026 at 7:00 PM
tomayac.com
👀 Look, ma! The Cross-Origin Storage extension running on Firefox! If you dare, install it via `about:debugging` from github.com/web-ai-commu.... Else, just wait for it to be approved on the Firefox Add-on Store. More background on #CrossOriginStorage: github.com/WICG/cross-o....
Cross-Origin Storage extension running in Firefox. Its popup window is open and shows resources being used across origins. The active tab is that of the extension's tests. All tests pass.
July 3, 2026 at 3:26 PM
tomayac.com
Super happy to announce that I'll be presenting about the #CrossOriginStorage API at #JSNationUS 2026: gitnation.com/badges/jsnat.... Click this link to sign up for partial free streaming access!

Here's the talk's abstract: gitnation.com/contents/cro....
Check out my badge & claim your free JSNation US 2026 remote ticket!
Join 5k engineers worldwide at JSNation US 2026 and meet 50+ top speakers at November 16 - 19, 2026
gitnation.com
August 6, 2026 at 10:04 AM
tomayac.com
🎧 I was a guest of @codepo8.bsky.social again for the @wearedevelopers.bsky.social podcast to talk about the #CrossOriginStorage API: www.wearedevelopers.com/videos/2162-.... Happy listening! (Find all related resources on the Awesome Cross-Origin Storage 😎 list: github.com/tomayac/awes...)
Chris and Tom, both wearing headphone, in a side-by-side view during the podcast recording.
September 3, 2026 at 1:37 PM
tomayac.com
If you want to experience Cross-Origin Storage (COS) in two real browsers, I managed to add full imperative COS API support (`navigator.crossOriginStorage`) to both @servo.org and Ladybird (personal prototypes): github.com/tomayac/awes....
#CrossOriginStorage
GitHub - tomayac/awesome-cross-origin-storage: A curated list of resources for the Cross-Origin Storage (COS) API
A curated list of resources for the Cross-Origin Storage (COS) API - tomayac/awesome-cross-origin-storage
github.com
August 7, 2026 at 10:27 AM
tomayac.com
🤩 Fantastic article by @nucliweb.net on HTTP cache partitioning and the #CrossOriginStorage API: joanleon.dev/en/http-cach.... Try the embedded demos with the COS extension installed or in one of the experimental browser builds (see the Awesome Cross-Origin Storage list: github.com/tomayac/awes...).
HTTP cache partitioning: the same image, downloaded twice | Joan León
A page with a cross-site iframe requests the same image from the iframe and from the parent. Chrome downloads it twice; Firefox and Safari, once. Why the cache key differs across the three engines, wh...
joanleon.dev
August 28, 2026 at 3:12 PM
tomayac.com
You can now download the macOS binary with this feature (☝️) enabled from github.com/tomayac/Chro.... (Launch Chromium, open `about://flags`, search for Cross-Origin Storage, set it to Enabled, and restart when prompted.) #CrossOriginStorage
github.com
September 21, 2026 at 2:35 PM
tomayac.com
I've now filed (or commented on existing) standards position requests from other browser vendors (WebKit & Mozilla) and the W3C TAG for the #CrossOriginStorage API:

* Mozilla: github.com/mozilla/stan...
* WebKit: github.com/WebKit/stand... 🆕
* W3C TAG: github.com/w3ctag/desig... 🆕
Cross-Origin Storage (COS) · Issue #1427 · mozilla/standards-positions
Specification title Cross-Origin Storage (COS) Specification or proposal URL (if available) No response Explainer URL (if available) https://github.com/WICG/cross-origin-storage/ Proposal author(s)...
github.com
August 5, 2026 at 4:34 PM
tomayac.com
I was once again a guest on the German-speaking 🇩🇪 @workingdraft.de podcast 🎙️ to talk about the Cross-Origin Storage API: workingdraft.de/723/. thoroughly enjoyed chatting about this exciting API proposal with @schepp.dev and @sirpepe.bsky.social. Track #CrossOriginStorage for more.
Revision 723: Cross-Origin Storage API – Caching über Origins hinweg, mit Thomas Steiner | Working Draft
Wir sprechen mit Thomas Steiner (Mastodon, Bluesky, LinkedIn) von Google über einen neuen Vorschlag für die Webplattform: die Cross-Origin-Storage API. Tom war bereits mehrfach bei uns zu Gast, zuletz...
workingdraft.de
August 4, 2026 at 6:14 PM
tomayac.com
Another #CrossOriginStorage API DevTools exploration: showing some metadata for resources on the Public Hash List (github.com/WICG/cross-o...), so the entries in the table are more than opaque hash strings.
Chrome DevTools showing multiple resources in Cross-Origin Storage. The metadata of the selected resource (that is on the Public Hash List) shows that the resource is from the list's Hugging Face section and belongs to the Whisper Tiny AI model.
September 17, 2026 at 5:20 PM
tomayac.com
Early Chrome DevTools exploration for debugging the #CrossOriginStorage API. This shows global stats first and then per-origin stats, here inspecting Three.js.

- (WIP) backend CL: chromium-review.googlesource.com/c/chromium/s...
- (WIP) frontend CL: chromium-review.googlesource.com/c/devtools/d...
Descent game on the left. The right side shows Chrome DevTools on the Application tab with a new "Cross-origin storage" section.
August 24, 2026 at 5:49 PM
tomayac.com
DevTools and browser Settings UI exploration for the #CrossOriginStorage API is coming along nicely. What would you expect to see in both DevTools and Settings? Let me know!
DevTools in Chrome, exploring a resource stored in Cross-Origin Storage. Chrome Settings page for Cross-Origin Storage, showing the files in Cross-Origin Storage, ordered by size with usage stats for each entry.
September 1, 2026 at 5:06 PM
tomayac.com
The Cross-Origin Storage extension was now approved for the Firefox Add-on Store: addons.mozilla.org/en-US/firefo.... 🦊 🧩 #CrossOriginStorage
Cross-Origin Storage – Get this Extension for 🦊 Firefox (en-US)
Download Cross-Origin Storage for Firefox. Implements the proposed Cross-Origin Storage API, letting sites share files with your consent for a faster and more efficient web.
addons.mozilla.org
July 6, 2026 at 5:31 PM
tomayac.com
macOS users interested in #CrossOriginStorage: you can now run a test build with the API behind a flag 🚩: github.com/tomayac/Chro.... In `about://flags`, search for Cross-Origin Storage, set it to Enabled, restart when prompted. To un-quarantine the app, see github.com/tomayac/Chro....
github.com
August 20, 2026 at 11:27 AM
tomayac.com
I'm keeping track of the learnings in the implementation notes (github.com/WICG/cross-o...), which hopefully will be useful for other vendors. #CrossOriginStorage
github.com
August 7, 2026 at 10:27 AM
tomayac.com
For the first time you can try the #CrossOriginStorage API on a "real" browser—after the still in-development browsers [shells] Servo and Ladybird: I managed to implement the API in proper Firefox 🦊: github.com/tomayac/awes... (Note that all of those are personal experimental builds.)
GitHub - tomayac/awesome-cross-origin-storage: A curated list of resources for the Cross-Origin Storage (COS) API
A curated list of resources for the Cross-Origin Storage (COS) API - tomayac/awesome-cross-origin-storage
github.com
August 11, 2026 at 10:19 AM
tomayac.com
I have a new unofficial macOS Chromium build out for you to test with #CrossOriginStorage API support and full DevTools integration: goo.gle/cos-chromium. Remember to set the Cross-Origin-Storage flag in `chrome://flags/#cross-origin-storage` and find Cross-origin storage on the Application tab.
Chromium running Quake with the Chrome DevTools Application panel open and the Cross-origin storage section selected, showing Three.js being shared between two origins.
August 27, 2026 at 4:57 PM
tomayac.com
Akaash Parthasarathy from the WebLLM team has filed WebKit and Mozilla feature request bugs asking for #CrossOriginStorage API support in Firefox and Safari:

🧭 bugs.webkit.org/show_bug.cgi...
🦊 bugzilla.mozilla.org/show_bug.cgi...

(Chrome's implementation bug is crbug.com/547587764.)
324017 – Support Cross-Origin Storage for reuse of WebLLM model artifacts across sites
bugs.webkit.org
September 14, 2026 at 11:43 AM