Almost all of the major WebView implementations I can think of are open source: • WKWebView (iOS, macOS): https://github.com/WebKit/webkit/blob/main/Source/Web

Almost all of the major WebView implementations I can think of are open source: • WKWebView (iOS, macOS): https://github.com/WebKit/webkit/blob/main/Source/WebKit/UIProcess/API/Cocoa/WKWebView.mm https://github.com/WebKit/webkit/blob/main/Source/WebKit/UIP... • Android WebView: https://android.googlesource.com/platform/frameworks/base/+/a5408e6/core/java/android/webkit/WebView.java https://android.googlesource.com/platform/frameworks/base/+/... • Mozilla GeckoView: https://github.com/mozilla/gecko-dev/tree/master/mobile/android/geckoview https://github.com/mozilla/gecko-dev/tree/master/mobile/andr... • Chromium Embedded Framework (CEF): https://bitbucket.org/chromiumembedded/cef/src/master/ https://bitbucket.org/chromiumembedded/cef/src/master/ The main ones that aren't open source are the Windows WebView and WebView2 components.