itch.io HTML5 Build Shows Blank Screen - MIME Types and WASM Entry Fix - How to Fix

Problem: Your game uploads to itch.io successfully, but players only see a blank screen when opening the HTML5 build.

Common symptoms:

Canvas appears but nothing renders
Browser console shows .wasm or .data load errors
Game works locally but fails on itch.io embed
Audio may initialize, but gameplay never starts

This issue is usually a deployment configuration mismatch, not a gameplay bug.

Root cause

A blank HTML5 page on itch.io is most often caused by one or more of these:

Incorrect MIME handling for WebAssembly or compressed assets
Wrong loader or data file paths after upload
Build folder structure mismatch with engine export expectations
Missing startup file reference in embedded index
Caching stale assets from older uploads

If the browser cannot fetch and execute the expected startup chain, you get a silent or near-silent blank screen.

Quick fix checklist

Rebuild HTML5 export in release mode with clean output folder.
Verify all referenced files exist in uploaded itch build (loader, wasm, data, framework files).
Confirm relative paths in index.html match uploaded folder layout.
Remove stale cached files and retest in private/incognito window.
Check browser console for exact first failing request and fix that first.

Step 1 - Verify exported file integrity before upload

Before publishing:

Open export locally from a static local web server (not direct file open)
Confirm no missing file requests in browser network tab
Validate that generated loader and wasm files are present and readable

If local server run already fails, fix export settings first before touching itch.io.

Step 2 - Validate path references in startup HTML

In your exported index.html or loader config, ensure:

Paths are relative to upload root
Filename case matches exactly
No stale hardcoded directories from previous builds

One incorrect character in a loader path is enough to produce a full blank-screen launch.

Step 3 - Check MIME and compression compatibility

Web exports often use compressed assets. If the host or runtime path expects a different encoding, startup fails.

For reliable first-pass debugging:

Temporarily test without compression if your engine supports it
Compare console output between compressed and uncompressed builds
Re-enable compression only after successful baseline load

This isolates MIME/encoding issues from core runtime issues.

Step 4 - Re-upload with clean package structure

Upload only required runtime files for the current build, not mixed old/new artifacts.

Good practice:

Delete old build bundle on itch project
Upload fresh export archive
Reconfigure launch target to current index.html
Save and test immediately

Mixed-version bundles are a frequent source of phantom blank screens.

Step 5 - Run a browser diagnostics pass

Use DevTools and check first failing request:

404 on wasm/data/framework
incorrect content type warnings
script parse failures
CORS or blocked request signals

Fix failures in order. Do not change multiple variables at once.

Verification checklist

Run these checks before final publish:

Open build in incognito mode
Launch on desktop Chrome and Firefox
Confirm first frame appears within expected startup window
Confirm input and audio initialize properly
Refresh once to verify cache-safe reload

Success target:

No blank screen
No critical network fetch failures
Stable startup on two browsers

Alternative fixes

If Unity WebGL build is affected

Re-check generated Build/ folder references and ensure template paths were not manually edited to stale filenames.

If Godot HTML5 build is affected

Confirm export preset output names and wasm file path exactly match the HTML shell references.

If only embedded itch page fails but standalone file host works

Review itch page embed settings and startup target file path for mismatch.

Prevention tips

Keep a small deployment checklist next to your export pipeline.
Version build folders by timestamp or semantic release tag.
Avoid manual renaming of wasm/data files after export.
Store one known-good web export baseline for quick regression comparison.

FAQ

Why does it work locally but fail on itch.io

Local runs often use different path assumptions and cache state. Hosting context exposes path and MIME mismatches quickly.

Should I disable compression permanently

No. Use uncompressed mode for debugging baseline startup, then re-enable optimized output once deployment is stable.

Do I need to clear browser cache every test

For troubleshooting, yes. Cached old loader/data pairs can hide or mimic deployment issues.