If you're looking to fiddle with code before you set up a local development environment, these web apps are custom-built for Ethereum smart contract development.
Remix - Web-based IDE with built in static analysis, and a test blockchain virtual machine.
EthFiddle - Web-based IDE that lets you write, compile, and debug your smart contract.
Ethereum Studio - Web-based IDE ideal for new developers looking to experiment with smart contracts. Ethereum Studio features multiple templates, transaction logger, and a built in-browser Ethereum Virtual Machine (EVM) to help you get started building on Ethereum as fast as possible.
Most established IDEs have built plugins to enhance the Ethereum development experience. At a minimum, they provide syntax higlighting for smart contract languages.
Visual Studio Code - Professional cross-platform IDE with official Ethereum support.
Atom - A hackable text editor for the 21st Century
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