Serialize and Unserialize PHP arrays and others strings.
Base64 encode your images (jpg, gif, png, svg, etc.) to include them directly in a CSS style sheet.
Base64 decode Url Safe.
Use JSON Edit to compose your JSON object strings.
Use JsFiddle to develop simple CSS and jQuery snippets.
Verify the availability of a website from various locations.
View if and IP is blacklisted for sending emails.
CSS to SCSS online
CSS Media Queries for iPads and iPhones.
Google Structured Data Testing Tool
HTML5 validator and outliner
Can I Use this feature in that browser?
Find unclosed HTML tags
HTML5 Living Standard