When comparing ButterCMS vs Netlify CMS, the Slant community recommends Netlify CMS for most people. In the question“What are the best open source headless CMS's?” Netlify CMS is ranked 6th while ButterCMS is ranked 13th. The most important reason people chose Netlify CMS is:
Experimental support for GitHub's GraphQL API is now available for the GitHub backend. Without mutation.
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Pros
Pro Integrate with any language/framework
Pro Experimental support for GitHub's GraphQL API
Experimental support for GitHub's GraphQL API is now available for the GitHub backend. Without mutation.
Pro Easy Creating Custom Widgets option
The NetlifyCMS exposes a window.CMS global object that you can use to register custom widgets, previews, and editor plugins. The same object is also the default export if you import Netify CMS as an npm module. The available widget extension methods are listed here.
Pro Modern
Pro Open-source
Pro Built in React.js
Cons
Con Not really open-source
Although API and SDK's are available on GitHub, the CMS source code is not.
Con A lot of configuration
Example: a few plugins and some code are needed for gatsby-img or markdown to work.