New Dev Tools is one of the best verified hub for free online tools.

It has cool features like

Editors:
JSON Editor Validator
API Editor
API Tester
YML Editor
Color Picker

Converter:
XML- JSON-Java Script
Color Code converter
Unit Converter
Encoder Decoder
Encryption Decryption

Validator:
JSON
XML
YML


Utils:
Calculator
File Diff Checker

Image:
Tiny PNG