Web Export in Godot 4.3+

Ship a Godot 4.x game as HTML5/WebAssembly. This covers what is different from a desktop export: the renderer, threading and server headers, browser interop, persistence, and the input and audio rules browsers enforce. All examples target Godot 4.3+ with no deprecated APIs.

C# projects cannot export to Web in Godot 4 — the .NET editor refuses the export (still true in 4.7.2). The code in this skill is GDScript only for that reason; a C# game that needs a browser build must be ported to GDScript or stay on Godot 3.

Related skills: export-pipeline for presets, CLI export and CI/CD, web-services for HTTP and WebSockets from the browser, rendering-pipeline for what the Compatibility renderer can and cannot do, audio-system for buses and playback, save-load for save formats.

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1. What Changes on Web

Area	On Web
Renderer	Always Compatibility (WebGL 2) — rendering/renderer/rendering_method.web defaults to gl_compatibility. No SDFGI, VoxelGI, volumetric fog, SSR, FSR, or screen-space AA
Scripting	GDScript and GDExtension only. No C#
Threads	Optional. Off by default; turning them on needs special server headers (Section 3)
Audio	Sample playback through the Web Audio API by default — AudioEffects on buses do not apply (Section 6)
Files	user:// lives in the browser's IndexedDB; there is no access to the player's disk except downloads and file-picker uploads
Networking	HTTP via the browser's fetch (CORS applies), WebSockets and WebRTC only — no raw TCP/UDP, so no ENet
Processes	No OS.execute(), OS.create_process(), or quitting the tab

Design for this from the start if web is a primary target. Porting a Forward+ game late means re-lighting it.

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2. The Export Preset

Add a Web preset in Project → Export (export templates must be installed). The options that matter:

Option	Default	Set it when
variant/thread_support	false	You need threads and can serve COOP/COEP headers (Section 3)
variant/extensions_support	false	The project uses GDExtension (needs the extension's web build)
vram_texture_compression/for_desktop	true	S3TC/BPTC textures for desktop browsers
vram_texture_compression/for_mobile	false	Turn on for phone browsers (ETC2/ASTC); costs a second texture set in the PCK
html/canvas_resize_policy	Adaptive	None / Project when embedding in a fixed-size page element
html/focus_canvas_on_start	true	Keep on so keyboard input works without a first click
html/experimental_virtual_keyboard	false	Mobile browsers need an on-screen keyboard for LineEdit
html/head_include	empty	Extra <head> tags — analytics, meta tags, fonts
html/custom_html_shell	empty	Replace the whole loading page with your own template
progressive_web_app/enabled	false	Installable, offline-capable build (Section 4)
threads/emscripten_pool_size, threads/godot_pool_size (Godot 4.5+)	8, 4	Only shown with thread support; lower them to reduce memory

The output is an .html page plus .js, .wasm, .pck, and audio worklet files — upload all of them together. The default filename for the page should be index.html for most hosts.

CLI export works as on desktop: godot --headless --export-release "Web" build/web/index.html.

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3. Threads or No Threads

Threaded builds use SharedArrayBuffer, which browsers only enable on a cross-origin isolated page. The server must send both headers on every file of the export (the page, its scripts, and the worker scripts):

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

	No threads (default, Godot 4.3+)	Threads
Hosting	Any static host	Needs the two headers above, or the PWA workaround
Audio	Sample playback, low latency	Sample playback by default; stream mode crackles more
Embeds, ads, third-party iframes	Work	Break unless they also send CORP/CORS headers (require-corp blocks them)
WorkerThreadPool	Tasks run inline on the main thread, so heavy work stalls frames	Real background threads
Thread	start() returns OK but the function never runs	Real background threads
Feature tag	nothreads	threads

Default to no threads. Turn them on only when profiling shows a real need (heavy procedural generation, physics on background threads), and you control the server or use a host that sets the headers. Code that must behave differently can check OS.has_feature("threads") — and any Thread-based code (level generation, loaders) must, or it silently does nothing on the default build. WorkerThreadPool is the portable choice.

Godot's own Remote Debug → Run in Browser server sends the headers, so a threaded build can work locally and fail once uploaded. Test on the real host.

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4. Hosting

Host	What to do
itch.io	Upload a ZIP with index.html at its root, set the project kind to HTML. For threaded builds tick SharedArrayBuffer support in the embed options
GitHub Pages, plain static hosts	No custom headers: ship the no-threads build, or enable PWA with progressive_web_app/ensure_cross_origin_isolation_headers (default true) so a service worker adds the headers after the first load
Your own server / CDN	Send COOP/COEP for threads, serve .wasm as application/wasm, and precompress .wasm and .pck with Brotli or gzip

Server config snippets (nginx, Apache, Netlify, Cloudflare Pages), compression, and cache headers: references/hosting.md.

The PWA option also makes the game installable and playable offline. After you publish an update, JavaScriptBridge.pwa_needs_update() turns true (and pwa_update_available is emitted); call JavaScriptBridge.pwa_update() to reload into the new version — it reloads every open tab.

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5. Detecting the Platform and Talking to JavaScript

<!-- csharp-parity: n/a — C# projects cannot export to Web in Godot 4, so web-only code paths are GDScript only -->

Use feature tags, not OS.get_name() string checks:

func _ready() -> void:
    if OS.has_feature("web"):
        $QuitButton.hide() # A tab cannot be closed from inside the game.
        if OS.has_feature("web_ios") or OS.has_feature("web_android"):
            _use_touch_controls()

web_android, web_ios, web_macos, web_windows, and web_linuxbsd read the browser's user agent. Use them to pick controls or quality, never as a security check.

JavaScriptBridge calls into the page. It exists on every platform but only does something on Web, so guard calls with OS.has_feature("web").

var _on_resize_cb: JavaScriptObject # Keep a reference, or the callback is collected and never fires.


func _ready() -> void:
    if not OS.has_feature("web"):
        return
    var window := JavaScriptBridge.get_interface("window")
    _on_resize_cb = JavaScriptBridge.create_callback(_on_browser_resize)
    window.addEventListener("resize", _on_resize_cb)
    var lang: String = JavaScriptBridge.eval("navigator.language", true)
    print("Browser language: ", lang)


func _on_browser_resize(args: Array) -> void:
    print("Browser resized: ", args[0].type)


func export_save_file(data: PackedByteArray) -> void:
    # Call from an input event (button press): browsers may block downloads that aren't.
    JavaScriptBridge.download_buffer(data, "savegame.dat")

Callbacks receive one Array holding the JavaScript arguments. eval() runs arbitrary JavaScript — never pass it strings built from player input or network data.

Uploads, calling functions defined in your HTML shell, and sending events to the embedding page: references/javascript-bridge.md.

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6. Audio

• Browsers block audio until the player interacts with the page. Start the game behind a "Click to play" screen (or the default loading page's click) so the first sound isn't swallowed.
• audio/general/default_playback_type.web is Sample: sounds are handed to the Web Audio API for low latency. AudioEffects on buses (reverb, filters, AudioEffectCapture, AudioEffectSpectrumAnalyzer) do not apply in this mode. Forcing Stream restores effects at the cost of latency and crackling — test before choosing it.
• Prefer Ogg Vorbis for music and short WAV for SFX; MP3 also works. See audio-system and assets-pipeline.

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7. Saving and Persistence

user:// is backed by IndexedDB and synced when a file is closed. ConfigFile, FileAccess, and ResourceSaver work unchanged.

<!-- csharp-parity: n/a — C# projects cannot export to Web in Godot 4, so web-only code paths are GDScript only -->

func save_settings(cfg: ConfigFile) -> void:
    cfg.save("user://settings.cfg") # Flushed to IndexedDB when the file closes.
    if OS.has_feature("web") and not OS.is_userfs_persistent():
        $SaveWarning.text = "Saves won't survive closing this tab (private browsing or storage blocked)."
        $SaveWarning.show()

• Private browsing, storage-blocking settings, and cleared site data wipe user://. Check OS.is_userfs_persistent() and tell the player.
• Storage is per origin: the same game on another domain (or a new itch.io upload URL) starts with empty saves. Offer export/import of save files (Section 5) for anything players would hate to lose.
• Browsers may evict storage under disk pressure. For accounts and cross-device saves use a backend — see web-services.

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8. Input, Window, and Performance Limits

Behavior	Rule
Fullscreen, mouse capture, pointer lock, clipboard writes	Only work from inside an input event handler (a click or key press), not from _ready() or a timer
Keyboard focus	Lost when the player clicks outside the canvas; keep html/focus_canvas_on_start on and show a "click to focus" hint
Browser shortcuts	Ctrl+W, Ctrl+T, F11 and similar may be handled by the browser, not the game — don't bind core actions to them
Frame rate	The browser drives frames with requestAnimationFrame; background tabs are throttled or paused, so pause the game on NOTIFICATION_WM_WINDOW_FOCUS_OUT
Memory	WebAssembly memory is limited; large levels and uncompressed textures crash low-end and mobile browsers first
Load size	Every megabyte of .pck and .wasm is downloaded before play — trim unused assets and compress on the server

Load-size checklist (export filters, texture formats, custom template builds without unused modules): references/hosting.md.

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9. Common Pitfalls

Symptom	Cause	Fix
Blank page, console says SharedArrayBuffer is not defined	Threaded build on a server without COOP/COEP	Export with thread support off, or add the headers
Works locally, fails after upload	The editor's test server sends headers your host doesn't	Test on the real host; ship no-threads
Opening index.html from disk fails	Browsers block WebAssembly from file://	Serve over HTTP, even locally
Game looks flat or dark compared to desktop	Compatibility renderer drops advanced lighting	Bake lightmaps; design for Compatibility (see rendering-pipeline)
No sound until the second click	Autoplay policy	Click-to-play screen before the first sound
Reverb/filters missing	Sample playback ignores bus effects	Accept it, or use Stream playback for that project
Saves gone next visit	Private window or new origin	Warn via is_userfs_persistent(); offer save export
HTTP requests fail only in the browser	CORS or mixed content	Fix server headers; HTTPS/WSS only (see web-services)
request_fullscreen / mouse capture ignored	Not called from an input event	Trigger it from a button press
Web export fails with "not supported in Godot 4 when using C#/.NET"	.NET editor builds cannot target Web	Port to GDScript, or export a GDScript-only project from the standard editor

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10. Checklist

• Project designed and lit for the Compatibility renderer
• No C# in the project; GDExtension only with variant/extensions_support and web binaries
• Thread support off unless needed and the host sends COOP/COEP (or the PWA service worker handles it)
• vram_texture_compression/for_mobile enabled if phone browsers are a target
• Tested on the actual host, not only the editor's Run in Browser server
• Click-to-play screen before audio starts; game pauses when the tab loses focus
• Fullscreen, mouse capture and downloads triggered from input events
• OS.is_userfs_persistent() checked; players can export important saves
• Quit button hidden on Web; platform checks use OS.has_feature("web")
• JavaScriptBridge callbacks stored in member variables; eval() never fed untrusted strings
• .wasm served as application/wasm; .wasm and .pck compressed on the server
• Download size checked; unused assets excluded from the Web preset