List of useful Online Tools when it comes to Android App development. Useful for both Xamarin (C#) and Android Studio (Java, Kotlin) developers.
Android Views Cheet Sheet
Quick examples for common controls
Can be used with Android Visualizer
Material color palette generator
Color is what it makes an app look beautiful. If you are getting started with an application and wonder which primary colors to choose? You can decide it better with material palette. It also provides icons and color variant.
Android Asset Studio
Icons generator online tool
An awesome collection of tools provided by Roman Nurik, to easily generate a variety of icons for your Android app. This tool comes in handy when you are creating a set of icons for your newly created app.
Material icons are delightful, beautifully crafted symbols for common actions and items. Download on desktop to use them in your digital products for Android, iOS, and web.
App Store Screenshot Generator
Create App Store & Google Play images
With this tool, you can now beautify your production app’s screenshots in seconds. The tool allows you to change the background, device frame, fonts, color based on your needs.
Screenshot & Mockup Generator
This tool serves the same purpose as the above tool with more eye-catching screenshots and even mockups (very limited for free accounts). Requires signup - (limited) free and paid accounts.
Collection of libraries and Tools
Though it can’t be considered as a "tool", it’s worth mentioning here as it has very rich list of tools and libraries. You can find here almost all open source libraries available for Android.