GENERATORS:
Text Content Generator - http://www.lipsum.com
Favicon Generator - http://tools.dynamicdrive.com/favicon
Data Generator - https://mockaroo.com/
Mobile Mockup Generator - https://mockuphone.com
Logo Generator - https://www.logaster.com
UUID Generator - https://www.uuidgenerator.net/
Hash Generator - https://passwordsgenerator.net/sha256-hash-generator/

IMAGE RESOURCES:
Free Stock Images - https://www.pexels.com
Free Stock Images With Great API - https://unsplash.com/
Free- Vectors, mockups - https://www.freepik.com
Dummy Image Placeholders - https://source.unsplash.com/
Dummy Image Placeholders - https://placeholder.com
Free Icons - https://www.iconfinder.com

CODE OPTIMIZATION:
Minify JS & CSS - http://minifier.org
Code Optimization Tools - https://codebeautify.org
Code Diff Checker - https://www.diffchecker.com

CONVERTERS:
ES6+ & JSX Compiler - https://babeljs.io/repl
Sass Converter - https://www.sassmeister.com/
Less Converter & More - http://www.webtoolkitonline.com
Markdown Editor - https://stackedit.io
Jade Converter - http://www.html2jade.org/

IMAGE COMPRESSION:
Compress All Images - https://compressor.io/compress
Compress JPG - http://jpeg-optimizer.com/
Compress PNG - https://tinypng.com/

VALIDATION & COMPATIBILITY:
Validate HTML - https://validator.w3.org
Validate CSS - https://jigsaw.w3.org/css-validator
Check Browser Compatibility - https://caniuse.com/
ES6+ Compatibility Table - https://kangax.github.io/compat-table/es6/

IN BROWSER CODING:
Client Side Code - https://codepen.io
Client Side Code - https://jsfiddle.net
Client Side Code - http://liveweave.com
Server Side Code - https://repl.it

SNIPPET TOOLS:
Snippet Manager - https://gist.github.com
Snippet Manager - https://pastebin.com

COLOR & DESIGN:
Create Color Schemes - https://color.hailpixel.com
Get Color Schemes of Websites - http://stylifyme.com
Create Gradients - https://uigradients.com
CSS Button Generator - http://css3buttongenerator.com
HTML Entity Lookup - http://entity-lookup.leftlogic.com/

RESPONSIVENESS:
Device Testing - http://www.responsinator.com
What's My Browser Size - https://www.webpagefx.com/tools/whats-my-browser-size/

WIREFRAME:
In Browser Wireframing - https://app.moqups.com
Very Basic In Browser Wireframing - https://wireframe.cc

SPEED TEST:
Speed & Performance Testing - https://tools.keycdn.com/speed
Pingdom Speed Test - https://tools.pingdom.com/
GT Metrix: - https://gtmetrix.com/