Places for your code
Observable is a better way to code. Discover insights faster and communicate more effectively with interactive notebooks for data analysis, visualization, and exploration.
See this introductory series to get up to speed.
Glitch is the friendly community where you'll build the app of your dreams.
CodePen is a social development environment for front-end designers and developers.
This is the simplest way I found to write React code like you would in a notepad. You can't save your work, but it's perfect for quick sketching. It also loads the latest version of React.
A detailed Webpack bundle analyzer.
Online GUI for optimizing SVG files with SVGO.
geojson.io is a quick, simple tool for creating, viewing, and sharing maps. geojson.io is named after GeoJSON, an open source data format, and it supports GeoJSON in all ways - but also accepts KML, GPX, CSV, GTFS, TopoJSON, and other formats.
A web-based data filtering tool for OpenStreetMap. With overpass turbo you can run Overpass API queries and analyse the resulting OSM data interactively on a map. There is an integrated Wizard which makes creating queries super easy.