Quick Look is one of the best macOS features—just press the spacebar while browsing files to instantly preview the one you've currently selected. This is great when you're browsing for images, videos, and documents, but can be less-than-ideal for plaintext files—there's no coloring for code and markdown isn't rendered—and some other file types aren't even supported.
Enter Peek, an $8 indie app that adds support for over 600 filetypes to Quick Look while also grafting on new features. It adds color highlighting for code, complete with customizable theming and rendering for Markdown. It also adds features that otherwise aren't offered in Quick Look, including a functional search and the ability to copy text.
To get started, install the app and start using Quick Look as usual. Preview a markdown file and it will be rendered, complete with a table of contents. Preview a file with code and it will be color coded.
A few of the best features aren't so obvious. First, you can now highlight text and copy it right from Quick Look, something not previously possible. You can now use the keyboard shortcut "Command-F" to search inside the document preview.
Note that these features are only added in files if Peek is the one providing the preview. Apple does not allow third party applications to take over preview functionality for certain filetypes, including PDF, txt, and office documents. You can tell if Peek is providing the file preview by looking for the pair of eye emoji at the end of the file name at the top of the window. (Note that while PDF files are not supported, ePDF files are.)
There are a number of other options worth checking out in the preferences, which you can find by launching the application. You can choose the color scheme for code highlighting, customize how markdown rendering works, and configure how postscript and ePDF files are rendered.
Peek is, in many ways, the ultimate Quick Look extension, especially if you work a lot with text files.
