HTML5 upload tips — the gotchas that waste an afternoon

A few things learned the hard way, so you don't have to: • Self-contained only. The sandbox blocks all outside requests, so no CDN scripts, no Google Fonts, no remote images. Inline your CSS/JS and embed assets as data URIs. • index.html at the root of the zip (or one wrapper folder, max). If it's buried deeper the uploader can't find it. • Test it from a plain file first. Open your index.html directly in a browser with no server — if it runs there, it'll run in the sandbox. • Saves and scores use postMessage to the parent, which just no-ops when there's no parent — so leaving those calls in never breaks local testing. • Keep it reasonable in size. There's a generous cap, but smaller loads faster and players notice. Anything else that bit you? Drop it here and I'll add it to the list.