Gwtar: A static efficient single-file HTML format

TIL about window.stop() - the key to this entire thing working, it's causes the browser to stop loading any more assets: https://developer.mozilla.org/en-US/docs/Web/API/Window/stop

Apparently every important browser has supported it for well over a decade: https://caniuse.com/mdn-api_window_stop

Here's a screenshot illustrating how window.stop() is used - https://gist.github.com/simonw/7bf5912f3520a1a9ad294cd747b85... - everything after <!-- GWTAR END is tar compressed data.

Posted some more notes on my blog: https://simonwillison.net/2026/Feb/15/gwtar/

I would like to know why ZIP/HTML polyglot format produced by SingleFile [1] and mentioned in the article "achieve static, single, but not efficiency". What's not efficient compared to the gwtar format?

[1] https://github.com/gildas-lormeau/Polyglot-HTML-ZIP-PNG

I was on board until I saw that those can't easily be opened from a local file. Seems like local access is one of the main use case for archival formats.

Very cool idea. I think single-file HTML web apps are the most durable form of computer software. A few examples of Single-File Web Apps that I wrote are: https://fuzzygraph.com and https://hypervault.github.io/.

The author dismisses WARC, but I don't see why. To me, Gwtar seems more complicated than a WARC, while being less flexible and while also being yet another new format thrown onto the pile.

Pretty cool. I made something similar (much more hacky) a while ago: https://github.com/AdrianVollmer/Zundler

Works locally, but it does need to decompress everything first thing.

It's fairly common for archivers (including archive.org) to inject some extra scripts/headers into archived pages or otherwise modify the content slightly (e.g. fixing up relative links). If this happens, will it mess up the offsets used for range requests?

The example link doesn't work for me at all in iOS safari?

https://gwern.net/doc/philosophy/religion/2010-02-brianmoria...

I will try on Chrome tomorrow.

Does this verify and/or rewrite the SRI integrity hashes when it inlines resources?

Would W3C Web Bundles and HTTP SXG Signed Exchanges solve for this use case?

WICG/webpackage: https://github.com/WICG/webpackage#packaging-tools

"Use Cases and Requirements for Web Packages" https://datatracker.ietf.org/doc/html/draft-yasskin-wpack-us...

I really don't understand why a zip file isn't a good solution here. Just because is requires "special" zip software on the server?

I gave up a long time ago and started using the "Save as..." on browsers again. At the end of the day, I am interested in the actual content and not the look/feel of the page.

I find it easier to just mass delete assets I don't want from the "pageTitle_files/" directory (js, images, google-analytics.js, etc).

Hmm, I’m interested in this, especially since it applies no compression delta encoding might be feasible for daily scans of the data but for whatever reason my Brave mobile on iOS displays a blank page for the example page. Hmm, perhaps it’s a mobile rendering issue because Chrome and Safari on iOS can’t do it either https://gwern.net/doc/philosophy/religion/2010-02-brianmoria...

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Gwtar seems like a good solution to a problem nobody seemed to want to fix. However, this website is... something else. It's full of inflated self impprtantance, overly bountiful prose, and feels like someone never learned to put in the time to write a shorter essay. Even the about page contains a description of the about page.

I don't know if anyone else gets "unemployed megalomaniacal lunatic" vibes, but I sure do.