What causes a Godot web export that will not load?

Godot 4 web builds need SharedArrayBuffer, which browsers only enable when the page is served with cross-origin isolation headers — without them the game stalls or errors on load.

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 Godot Web Export That Won't Load

Quick answer: Serve the build with the COOP and COEP headers that enable cross-origin isolation, host over HTTPS, and on platforms like itch.io enable the SharedArrayBuffer option.

A Godot web export that loads locally but hangs when hosted is almost always missing the cross-origin isolation headers SharedArrayBuffer requires. The game code is fine; the hosting is not. Here is the fix.

How to fix it

1. Send the cross-origin isolation headers

The server must return Cross-Origin-Opener-Policy: same-origin and Cross-Origin-Embedder-Policy: require-corp. These enable SharedArrayBuffer, which Godot 4 threads depend on. Without them the loader stalls.

2. Enable the option on hosting platforms

On itch.io, tick the SharedArrayBuffer support checkbox for the HTML project. Other static hosts need the headers configured explicitly or via a config file.

3. Serve over HTTPS from a proper server

Opening the file directly or over plain HTTP fails. Use a local server with the headers for testing and HTTPS in production, and check the browser console for the specific COOP/COEP error.

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 Godot 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.

Most of the time the fix is small. Seeing the failure clearly is the part that actually costs you.