What is the best language/framework for developing a REST API?

For such “simple” job there is no really difference in the advantages between languages. Though there are some pros and cons of course. If you are looking at building a JSON API, I will always recommend you to have a look at NodeJS and JavaScript since you will be working with JSON objects from the ground up since they’re native JavaScript objects.

Even so, nearly all languages out there have great package managers that can help you to take advantages of micro frameworks available to simplify your REST API building.

Often you’ll se the mentioning of “Sinatra like micro frameworks” which points towards the Ruby framework Sinatra which set a way of building simple APIs setting the routes in a simple way. Such frameworks are available for a lot of languages and I recommend it highly to have a look at such in a language of your comfort.

• Ruby Sinatra
• NodeJS ExpressJS
• PHP Slim
• .NET Nancy

These are of course only some examples and there are a lot more of these out there.

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I really like working with Microsoft's WebAPI framework. Sure Rails gets all the love, but the .NET framework especially ASP.NET has really made it super simple to get a JSON enabled REST API up and running with very little custom coding. Add ontop that it gives you a turn key OAuth user authn/authz solution which lets you go straight to implementing your web services without ever having to mess with any JSON or worry about de/serialization. The neckbeards may scoff at Microsoft's .NET, but one's fur must be especially thick to deny the power of the Visual Studio debugging environment. Visual Studio 2015 Community is absolutely free and gives you a set of debugging and analysis tools which make the task of debugging almost fun.