#crossoriginstorage — Public Fediverse posts

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!

🤩 Fantastic article by @nucliweb on HTTP cache partitioning and the #CrossOriginStorage API: https://joanleon.dev/en/http-cache-partitioning-cross-origin-storage/. Be sure to try the embedded demos with the COS extension installed or in one of the experimental browser builds. Find it all on the 😎 Awesome Cross-Origin Storage list: https://github.com/tomayac/awesome-cross-origin-storage.

I have a new unofficial macOS Chromium build out for you to test with #CrossOriginStorage API support and now also full DevTools integration: https://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, right under Cache storage.

Some early Chrome DevTools explorations for debugging the #CrossOriginStorage API. This shows global stats first and then per-origin stats, here inspecting the Three.js resource from Descent shared with Quake.

- (WIP) Chromium backend CL: https://chromium-review.googlesource.com/c/chromium/src/+/8270451
- (WIP) DevTools frontend CL: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/8277053

macOS users interested in #CrossOriginStorage: you can now run a test build with the Cross-Origin Storage API behind a flag 🚩: https://github.com/tomayac/Chromium/releases/download/chromium-cos-linux-x64-2026-08-17/chromium-cos-macos-arm64.zip. In `about://flags`, search for Cross-Origin Storage, set it to Enabled, restart when prompted. To un-quarantine the binary, see https://github.com/tomayac/Chromium/releases#:~:text=macOS%20on%20Apple%20Silicon%20(arm64).

🤩 It's happening!!1! I just sent the "Intent to Prototype" email for the #CrossOriginStorage API: https://groups.google.com/a/chromium.org/g/blink-dev/c/p5nq70aN63o/m/uNm_oaEOBQAJ. If you want to stay in the loop, star the ☂️ umbrella Chromium bug https://crbug.com/547587764 (and the subtask bugs: https://crbug.com/547587764/dependencies).

😎 Chromium (personal fork) passing all Web Platform Tests of the #CrossOriginStorage API.

* WIP CL: https://chromium-review.googlesource.com/c/chromium/src/+/8256403
* Runnable binary: https://github.com/tomayac/Chromium/releases (Linux x86_64)

Look, ma, that's WebKit 🧭 passing all Web Platform Tests for #CrossOriginStorage. And you can try it: https://github.com/tomayac/WebKit/releases (personal fork)! That's now four prototype implementations of the API in four different browsers: https://github.com/tomayac/awesome-cross-origin-storage#prototype-browser-implementations (all of them with releases you can run).

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 🦊: https://github.com/tomayac/awesome-cross-origin-storage/#prototype-browser-implementations (Note that all of those are personal experimental builds.)

See this progressively enhanced demo page for what these proposals would enable: https://web-ai-community.github.io/cross-origin-storage-extension/progressive-enhancement-demo.html!

(Try the demo without or with the #CrossOriginStorage extension installed: https://github.com/web-ai-community/cross-origin-storage-extension#available-on.)

Some more Cross-Origin Storage API updates: filed the required HTML issues (the CSS one already existed) toward better #CrossOriginStorage integration in the platform:

* Add `crossoriginstorage` attribute to `<link>` and `<script>`: https://github.com/whatwg/html/issues/12770
* Add `crossOriginStorage` JavaScript import attribute: https://github.com/whatwg/html/issues/12771
* Proposal for a new `<request-url-modifier>` called `<cross-origin-storage>`: https://github.com/w3c/csswg-drafts/issues/14056

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 and @ladybirdbrowser (personal prototypes): https://github.com/tomayac/awesome-cross-origin-storage#prototype-browser-implementations. I'm keeping track of the learnings in the implementation notes (https://github.com/WICG/cross-origin-storage/blob/main/browsers/cross-origin-storage-implementation-notes.md), which hopefully will be useful for other vendors. #CrossOriginStorage

📢 Super happy to announce that I'll be presenting about the #CrossOriginStorage API at #JSNationUS 2026: https://gitnation.com/badges/jsnation-us-2026/thomas_steiner_135298. Click this link to sign up for partial free streaming access!

Here's the talk's abstract: https://gitnation.com/contents/cross-origin-storage-a-shared-cache-for-the-web.

I've now filed (or commented on existing) standards position requests from other browser vendors (@webkit & @firefoxwebdevs) and the @tag for the Cross-Origin Storage API:

* Mozilla Standards Position request: https://github.com/mozilla/standards-positions/issues/1427 (already existed)

* WebKit Standards Position request: https://github.com/WebKit/standards-positions/issues/703 (new)

* W3C TAG Design Review request: https://github.com/w3ctag/design-reviews/issues/1254 (new)

#CrossOriginStorage

I was once again a guest on the German-speaking 🇩🇪 @workingdraft podcast 🎙️ to talk about the Cross-Origin Storage API: https://workingdraft.de/723/. thoroughly enjoyed chatting about this exciting API proposal with @Schepp and @sir_pepe. Track #CrossOriginStorage for more.

Cross-Origin Storage API: Stop Downloading Twice: https://dev.to/morellodev/cross-origin-storage-api-stop-downloading-files-twice-56kb. A great overview of our proposal for the #CrossOriginStorage API by Dennis Morello. 👏

The Cross-Origin Storage extension was now approved for the Firefox Add-on Store: https://addons.mozilla.org/en-US/firefox/addon/cross-origin-storage/. 🦊 🧩 #CrossOriginStorage

Started an Awesome Cross-Origin Storage list: https://github.com/tomayac/awesome-cross-origin-storage/ 😎. Transformers.js, WebLLM, wllama, Flutter, Emscripten, Nuxt and Vite plugins, and a bunch of demos… #Awesome #CrossOriginStorage

👀 Look, ma! The Cross-Origin Storage extension running on Firefox! If you dare, install it via `about:debugging` from https://github.com/web-ai-community/cross-origin-storage-extension. Else, just wait for it to be approved on the Firefox Add-on Store. More background on #CrossOriginStorage: https://github.com/WICG/cross-origin-storage. (FYI: @firefoxwebdevs and @krosylight)

I'm very excited to share a guest post I wrote for the Hugging Face 🤗 blog! Experimenting with the proposed Cross-Origin Storage API in Transformers.js!

👉 https://huggingface.co/blog/cross-origin-storage

This proposed new browser API, `navigator.crossOriginStorage.requestFileHandle(hash)`, has the potential of revolutionizing the Web, a little bit at least. Learn more at https://github.com/WICG/cross-origin-storage.

And Transformers.js aren't alone with this, they're joined by WebLLM, wllama, Flutter, and Emscripten.

#CrossOriginStorage