Every Developer needs tools for making the developing easier and faster.
This list is a summary of the lists I have found on the Internet .
Founded in 2008, Stack Overflow is the largest, most trusted online community for anyone that codes to learn, share their knowledge, and build their careers.
More than 50 million unique visitors come to Stack Overflow each month to help solve coding problems, develop new skills, and find job opportunities.
They have an impressive list of Q&A's.
CodeWall  says:
StackOverflow, a huge community of developers posting questions to be advised from other developers, it’s a stroke of genius.
Most developers will already of heard of this absolute gem. It’s on this list of tools because it is ultimately one of the best websites to use for gaining knowledge.
JSFiddle will render your code to an output window. It’s even capable of saving versions of your code that you can repost or send to other people.
- Codepen CodePen is pretty similar to JSFiddle but each pen automatically generates website integration code that you can paste directly into your site.
- DB Fiddle. Don’t have a database on your device? Then this tool is the perfect solution, simply add some SQL Syntax wrapped around data to create a temporary table. From there you can execute SQL statements on the table’s data and await the result.
- DotNeD Fiddle fiddle allows multiple configurations in languages and project types. Choose from C#, F# and Visual Basic for the language and select the project type from the drop-down, for instance, MVC. After configuration, write and run your code against the dot net engine.
JSONLint is invaluable when it comes to debugging JSON formatting.
Lint flags exactly where you’ve missed a comma or curly brace enabling rapid remedy.
Once JSONLint is happy your JSON is valid, you will be presented with a message to say its good to go.
A really great web tool if your working with complicated JSON.
WhatsMyFont can very cleverly analyze an image of any particular text.
The web app then checks it’s extensive font data for a match.
If one or matches are found, the website will present a list of the closest matches fonts with the links to their source.
It’s very handy if you see an image with a font you love but is no indication of what font style it is.
FavIcon-Generator. Upload a single image, usually a logo, this generator will parse your image and generate an icon pack with multiple sizes.
Each size has its own specific purpose.
Some for IOS shortcuts, Android shortcuts, and the general browser favorite icon.
Another speedy tool for web developers to save some time in an image editing tool.
Validators and Testers
There are several validator-websites.
- W3C Validator W3 Org validates your HTML-code with the proper hypertext markup language standards.
W3C will analyze your HTML, then point out the exact elements, if any, that doesn’t validate with the correct format.
It’s as simple as putting your website’s URL in and pressing the Check button.
- JigSaw is a validator for CSS-code. It works like Validator W3 Org.
- FreeFormatter xpath tester validates/helps you to test your xpath queries.
- Regex101 is a regular expression validator and tester.
- xDebug is a PHP debugging module that allows full functional debugging of code in an IDE.
Sometimes it’s a pain to set up, so xDebug made a page on their website where you can paste your PHP settings by printing phpinfo().
After the site analyses the PHP info settings, it specifies the exact module needed for that PHP build.
In addition, it even tells you how to add it to your project.
- PHP-Unit is a Unit Testing environment for PHP. Without unit-testing nobody can make solid-web-apps.
- PHP has a lint option embedded in the php-environment, however there are solutions that are a little bit better, such as: 
Essentially, it takes all of the white space and breaks out of the files.
After it’s been re-formatted, it’s pretty impossible to understand, but the size of the file will of reduced.
Quite simple the opposite of the Minifier tool.
AJAX and REST Services
If you want to test the correct working of your websites API-, REST- and AJAX calls, you must have Google Postman.
Postman leads the way in the API-first Universe. It is a complete solution.
- Get Postman, The home website