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How you talk to Unreal depends on how you embed the stream. All three paths can send AND receive — they just use different APIs.
PathSend to UEReceive from UE
Default frontend (share URL)URL query params: ?key=value (one-time, at launch)Built-in handlers — opens URLs, takes screenshots, shows keyboard, toggles cursor (see Default frontend)
Iframe postMessageiframe.contentWindow.postMessage(...)window.addEventListener('message', ...)
Web SDKemitUIInteraction(...), emitConsoleCommand(...)addResponseEventListener(...)
Pick one based on how you embed. Don’t mix the APIs across paths — even though everything ends up in the same UE message system, the frontend-side calls are different.

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Important — UE-side setup is the same

The Blueprint setup on the Unreal side is identical regardless of which frontend path you use. Set it up once and it works for URL params, iframe postMessage, and the Web SDK.
Unreal sideBlueprints to receive frontend messages and send your own. Shared across all three paths.
Default frontendWhat the share link handles automatically, plus URL-param syntax.
Frontend side (URL params)Detailed URL syntax for one-time messages at launch.
Iframe communicationSend and receive via postMessage.
Web SDK communicationThe SDK’s programmatic methods and event listeners.