While there are very few "one-click" online tools for decompiling standard
— free, but desktop, not online.
If you are decompiling proprietary software, you may be violating the Terms of Service or copyright laws. Only decompile files you own or those that fall under fair use/educational purposes. exe decompiler online free link
If you are trying to decompile a modern .NET app, an "exe decompiler online free link" works like magic. If you are trying to decompile a video game driver or legacy C++ software, you will get assembly language. While there are very few "one-click" online tools