JavaScript Syntax Validator: Checks for mistakes and errors: https://esprima.org/demo/validate.html

JavaScript Beautifier This JavaScript code beautifier, cleaner tool allows you to tidy and optimize your code: https://html-cleaner.com/js/ or https://beautifier.io/

JavaScript Online Compiler https://rextester.com/l/js_online_compiler

W3Schools It is an educational website for learning web technologies online. https://www.w3schools.com/

JavaScript CheatSheet https://htmlcheatsheet.com/js/

JavaScript Compression https://jscompress.com/

jQuery CheatSheet List of common jQuery selectors etc. https://htmlcheatsheet.com/jquery/

jQuery Documentation https://api.jquery.com/

CSS to jQuery Converter http://www.beansoup.de/csstoscript.php

PHP Code Checker This free service performs a line-by-line analysis for common mistakes and errors in your PHP syntax and will not execute or save your code: https://phpcodechecker.com/

PHP Sandbox Test your PHP code with this code tester: http://sandbox.onlinephpfunctions.com/

PHP Beautifier Beautify dirty, ugly PHP code using Online PHP Beautifier and make your PHP code more readable. It gives the PHP code proper indentation with spaces or tabs. It also supports various indentation styles such as K&R style, Allman style, Whitesmiths style and GNU style: http://beautifytools.com/php-beautifier.php

Official PHP documentation https://www.php.net/manual/en/index.php

PHP: The Right Way tells you all the programming standards that might not be obvious to new developers. https://phptherightway.com/

SQL Syntax Check Validator https://www.eversql.com/sql-syntax-check-validator/

SQL Formater https://sqlformat.org/

HTML Formater Format your HTML, XML, CSS, JavaScript, PHP and JSON code in a few easy steps. https://webformatter.com/html

HTML Editor https://html-online.com/editor/

HTML Colors Get HTML color codes, Hex color codes, RGB and HSL values with our color picker, color chart and HTML color names https://htmlcolorcodes.com/

CSS Minifier CSS Minifier/Compressor https://cssminifier.com/

Regular Expression Tester https://regex101.com/

Font Awesome Icons https://fontawesome.com/v4.7.0/icons/

HTML color codes Find that perfect color with our color picker and discover beautiful color harmonies, tints, shades and tones https://htmlcolorcodes.com/