update

Add ButtonBuddy 2/4/2021
Add npm semver calculator npm trends WebpageTest and BUNDLEPHOBIA 2/10/2021
Add PageSpeed Insights 2/16/2021
Add Image
Add squoosh 2/25/2021
Add coolors 3/18/2021
Add {JSON} Placeholder 3/25/2021
Add Happy Hues, CSS Peeper, Get Waves, gradienta, Type Scale
Add Bootstrap 5 Cheatsheet and Devhints 7/31
Create a site for this post https://frontend-tools.vercel.app

TS/JS

Bit.dev

Bit is a scalable and collaborative way to build and reuse components. It's everything you need from local development to cross-project integrations.
https://bit.dev/

Create App

config.js generator for webpack, Parcel, and Snowpack
Create App supports react, svelte, and vue.
https://createapp.dev/

TypeScript Playground

TypeScript Playground is useful to check the latest version's typescript's features.
https://www.typescriptlang.org/play

JavaScript Minifier

Actually, there are some CLI tools and functionalities to minify js, but this can be useful when you don't use any module bundlers and task runners. It's easy to use since we just need to copy and paste js code.
https://javascript-minifier.com/

unminify (js/css/html/xml/json)

This can be useful when you work on xxx.min.js and need to check the code for debugging.
https://unminify.com/

openbase

openbase is a very useful website when you are looking for npm packages for your project since we can see other developers' reviews about the packages.
https://openbase.io

@types search

Search engine for @types files
https://www.typescriptlang.org/dt/search?search=

Prettier Playground

https://prettier.io/playground/

JSLint

Probably most of you use eslint, but when you don't want to use any packages for lint, this might be good.
https://jslint.com/

JWT.IO

JSON Web Tokens are an open, industry-standard RFC 7519 method for representing claims securely between two parties.
JWT.IO allows you to decode, verify and generate JWT.
https://jwt.io/

npm semver calculator

npm version calculator
https://semver.npmjs.com/

npm trends

A tool allows us to check an npm package's trend such as the number of downloads, starts, and issues.
https://www.npmtrends.com/

BUNDLEPHOBIA

Find the cost of adding an npm package to your bundle
https://bundlephobia.com/

CSS

CSS Gradient

CSS Gradient is a happy little website and free tool that lets you create a gradient background for websites.
https://cssgradient.io/

CSS clip-path maker

The clip-path property allows you to make complex shapes in CSS by clipping an element to a basic shape (circle, ellipse, polygon, or inset), or to an SVG source.
https://bennettfeely.com/clippy/

Layoutit!

Layoutit generates CSS for grid design.
https://grid.layoutit.com/

ButtonBuddy

https://buttonbuddy.dev/
Accessible Button Contrast Generator

HTML

Placeholder.com

Placeholder.com is a free image placeholder service for web designers, serving billions and billions of images each year.
https://placeholder.com/

Happy Hues

Happy Hues is a color palette inspiration site that acts as a real-world example as to how the colors could be used in your design projects.
https://www.happyhues.co/

CSS Peeper

Smart CSS viewer tailored for Designers
https://csspeeper.com/

gradienta

Multicolor Gradients
Pure CSS Code, JPG Download, Open Source!
https://gradienta.io/

Image

Get Waves

Make some waves (SVG)
https://getwaves.io/

Cheatsheets

Bootstrap 5 CheatSheet 🚀

https://bootstrap-cheatsheet.themeselection.com/
An interactive list of Bootstrap 5 classes, variables, and mixins. 🎁 The only Bootstrap 5 CheatSheet you will ever need. 🎊

Devhints

https://devhints.io/
A collection of cheatsheets for developers.
Covers FE, BE and others.

other

CanIUse

https://caniuse.com/

favicon.io

The only favicon generator you need for your next project. Quickly generate your favicon from text, image, or choose from hundreds of emojis.
https://favicon.io/