Ship a web game that loads fast (a practical checklist)

If players can’t start playing in seconds, they bounce. This tutorial is a practical checklist you can apply to almost any web game stack (Canvas/WebGL/WebGPU, Pixi/Three/PlayCanvas, custom engine, etc.).

1) Set budgets first (or you can’t optimize)

Pick budgets that match your target device. A solid default for an “instant play” experience:

• JS+CSS shipped: under ~300–500 KB gzip (smaller is better)
• Critical assets before first input: under ~2–5 MB compressed
• Time to first input: under ~3–5 seconds on mid mobile

Write these down and treat them like API contracts.

2) Measure the right things

In Chrome DevTools:

• Use Performance to capture a session and inspect long tasks.
• Use Network to check:
  • transfer size vs. decoded size
  • caching headers
  • whether assets stream progressively or arrive as one giant blob

In game terms, track:

• “Can the player move?” time
• “First meaningful frame” time
• “First input latency” (input → frame)

3) Compress everything you can

Make sure your hosting serves:

• Brotli (br) for text assets (JS/CSS/HTML/WASM) when available
• gzip as fallback

For WebAssembly builds, compression is often the difference between “instant” and “never loads.”

4) Don’t download the whole world upfront

Split your game into:

• Boot: minimal loader + input + first scene
• Core: main gameplay systems
• Optional: extra levels, cosmetics, high-res textures, bonus audio, etc.

Load “Optional” only after:

• the player can already play, and/or
• you know they want that content (e.g. they reached a menu/level)

5) Choose the right asset formats

For most web games:

• Images: prefer WebP (or AVIF if you can tolerate slower encode) for UI/backgrounds.
• Audio: prefer Ogg Vorbis for general use; test AAC for Apple ecosystems.
• Video: prefer MP4/H.264 for compatibility, WebM when supported and smaller.

Keep an eye on decode cost: “smaller download” can still be “slower to decode.”

6) Keep your first scene small and deterministic

Avoid these in your first interactive scene:

• shader compilation storms
• huge texture uploads
• procedural generation that blocks the main thread
• synchronous JSON parsing of megabyte blobs

If you must do heavy work, do it:

• incrementally across frames, or
• in a Worker (when possible)

7) Cache aggressively (but correctly)

Use long-lived caching for content-addressed assets:

• Cache-Control: public, max-age=31536000, immutable

For HTML entrypoints, keep caching short so you can deploy updates safely.

8) Make “failure” fast and readable

If something goes wrong, show:

• a clear error message
• a retry button
• a link to report the issue

Silent failures kill trust.

9) If you use Wasm threads, understand COOP/COEP

If your build depends on SharedArrayBuffer (common for some Wasm threading setups), you’ll likely need cross-origin isolation headers:

• Cross-Origin-Opener-Policy: same-origin
• Cross-Origin-Embedder-Policy: require-corp

Test early on your real host, because headers and third‑party embeds can break things.

10) Make it playable without an SDK

If you’re targeting Cinevva’s creator workflow, aim for:

• one URL that boots reliably
• no required logins to start a demo
• predictable input controls

Then you’re ready for distribution without integrating extra SDKs.

Related:

• For game creators
• AI-generated content policy