What causes a web game not loading after uploading the zip to itch.io?

itch.io serves the uploaded zip but needs an index.html at the zip root and the correct embed options, so a nested index, missing file, or unset isolation option leaves the player blank.

How do I catch this when it only happens for some players?

Capture it automatically from the player's device with the full stack trace, the device and OS, the build, and a breadcrumb trail of what they did. That turns a vague complaint into a specific, reproducible issue you can fix without owning the hardware it happens on.

How to Fix a Web Game Not Loading After Uploading the Zip to itch.io

Quick answer: Put index.html at the root of the zip, mark the upload as playable in browser, and enable SharedArrayBuffer support if the build is threaded.

Your HTML5 game runs locally but shows a blank frame on itch.io because the index is nested or an embed option is wrong. Fixing the zip layout and options fixes it.

How to fix it

1. Put index.html at the zip root

Zip the contents of the build folder, not the folder itself, so index.html sits at the top level of the archive. A nested build/index.html makes itch.io load nothing.

2. Mark it playable in browser

In the upload settings, set the file kind to HTML / This file will be played in the browser and configure the viewport size so the player frame embeds the game.

3. Enable isolation for threaded builds

If the build needs SharedArrayBuffer, turn on itch.io's SharedArrayBuffer support option so it serves the COOP/COEP headers; otherwise the threaded build fails to start.

Catching the ones you can't reproduce

The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.

Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.

This is where a tool like Bugnet earns its place. Its SDK captures every HTML5 error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.

Reproduce it once with full context and the fix writes itself. The hunt is the expensive part.