Some helpful bookmarks

Cyberchef - Swiss-army too for conversions and data
Mockbin - Mockbin allows you to generate custom endpoints to test, mock, and track HTTP requests & responses between libraries, sockets and APIs.
Httpbin - A simple HTTP Request & Response Service.
Json Formatter & Validator - Validates and formats json
Cloud Design Patterns - These design patterns are useful for building reliable, scalable, secure applications in the cloud.