自2012年(当这个问题被创建时)GitHub本身可以:

在常规存储库中创建并显示Markdown文档的预览(自2011年8月以来一直如此) 或者，如果你不想直接影响你的存储库，对gist做同样的事情(自2020年12月起) 即使没有提交要点，自2021年11月起，您也可以在您正在编辑(但尚未提交)的要点中预览Markdown文档

一旦要旨的预览看起来不错，你就可以将要旨的标记复制到你当地的README中。Md，添加，提交和推送。

有很多方法:如果你用的是Mac，使用Mou。

如果您想在浏览器中测试，您可以尝试StackEdit，正如@Aaron或Dillinger指出的那样，因为Notepag现在似乎已经关闭了。就我个人而言，我使用Dillinger，因为它可以将我所有的文档保存在浏览器的本地数据库中。

我通常只是直接在GitHub网站上编辑它，然后点击编辑窗口上方的“预览”。

也许这是自这篇文章以来添加的一个新功能。

你可以使用静态网站编辑器:在GitLab 13.0(2020年5月)中，它附带了一个所见即所得面板。

WYSIWYG for the Static Site Editor Markdown is a powerful and efficient syntax for authoring web content, but even seasoned authors of Markdown content can struggle to remember some of the less-frequently used formatting options or write even moderately-complex tables from scratch. There are some jobs better accomplished with a rich text, “What You See Is What You Get” (WYSIWYG) editor. GitLab 13.0 brings a WYSIWYG Markdown authoring experience to the Static Site Editor with formatting options for common formatting options like headers, bold, italics, links, lists, blockquotes, and code blocks. The WYSIWYG editor also removes the onerous task of editing tables in Markdown by letting you visually edit table rows, columns and cells in the same way you would edit a spreadsheet. For those more comfortable writing in raw Markdown, there’s even a tab for switching between WYSIWYG and plain text editing modes.

请参阅文档和版本。

同样，您只能使用它来编写README:一旦它看起来很好，您就可以将它报告给原始项目。 但重点是:你不需要任何第三方降价预览插件。

GitLab 14.2(2021年8月)

Preview Markdown live while editing Markdown is a fast and intuitive syntax for writing rich web content. Until it isn’t. Luckily, it’s easy to preview the rendered output of Markdown to ensure the accuracy of your markup from the Preview tab. Unfortunately, the context switch required to move between the raw source code and the preview can be tedious and disruptive to your flow. Now, in both the Web IDE and single file editor, Markdown files have a new live preview option available. Right-click the editor and select Preview Markdown or use Command/Control + Shift + P to toggle a split-screen live preview of your Markdown content. The preview refreshes as you type, so you can be confident that your markup is valid and will render as you intended. See Documentation and Epic.

参见GitLab 14.6(2021年12月)

Toggle wiki editors seamlessly Toggle wiki editors seamlessly Editing wiki pages with the new rich Markdown editor makes it easier for everyone to contribute regardless of how well they know Markdown syntax. You may also prefer to write raw Markdown in some situations, but use the WYSIWYG interface for more complex or tedious formatting tasks, like creating tables. Previous versions of GitLab required you to save changes before switching between the rich Markdown editor and the Markdown source, adding more steps and friction to your edits. In GitLab 14.6 you can now seamlessly switch between the two editing experiences without committing your changes, choosing the editor that suits your needs at any given moment. See Documentation and Issue.

参见GitLab 15.6(2022年11月)

Default split view for Markdown preview in the Web Editor The ability to preview Markdown files side by side while editing was introduced in GitLab 14.2. With this release, we’ve made the split view the default experience for previewing Markdown in the Web Editor. In the Preview tab, you can now see a live Markdown preview that updates as you type alongside your content. This way, you can be confident that your markup is valid and renders as you intended without having to switch between the Write and Preview tabs. See Documentation and Issue.

Atom工作得很好-只需打开Markdown文件，并按Ctrl+Shift+M切换Markdown预览面板旁边。它还处理HTML和图像。

你可以安装chrome扩展“Markdown Viewer”: https://chrome.google.com/webstore/detail/markdown-viewer/ckkdlimhmcjmikdlpkmbgfkaikojcbjk?hl=en