Install the app and run it. This will register the availability of the app’s QuickLook extensions, Yaml Previewer and Yaml Thumbnailer. You can now quit the app: just click OK:
To use QuickLook in Finder, select a YAML file — one with the extension
.yaml, for example — and press space. This will pop up a rendered preview of the file:
You will also see YAML file previews in Finder’s preview pane, enabled using View > Show Preview or by hitting Cmd-Shift-P, and in the Preview: section of Finder’s file info panel (select a file and hit Cmd-I).
You can disable or re-enable Yaml Previewer and/or Yaml Thumbnailer in System Preferences > Extensions:
For some background information on how Catalina delivers QuickLook previews, you might like to read this blog post.
Open the Preferences panel from the main app’s PreviewYaml menu. This allows you to adjust some of the key elements of the preview:
Choose your preferred text size using the slider, then pick the monospace font you want the file to be presented in:
You can also choose each font’s style:
Choose your preferred key colour by clicking the colour well to pop up macOS’ colour picker. As you make your colour selection, the colour well will be updated:
Click Save to apply your choices.
Changing these settings will affect previews straight away, but may not affect thumbnails until you open a folder that has not been previously opened during the current login session.
You can use the main app to submit feedback. Just click in the Send Feedback button in the main window, or select Report a Bug… from the Help menu:
If PreviewYaml reports that it was unable to render YAML, this is almost certainly caused by a malformation of the YAML itself — the error message should help you spot the problem. PreviewYaml’s YAML library is quite strict, so YAML malformations which other apps allow may be rejected by PreviewYaml. For this reason, you can optionally tell PreviewYaml to display a file’s raw YAML in the event of a parsing error. This option is chosen in the Preferences panel and will allow you to QuickLook even bad YAML files, just without rendering.
PreviewYaml currently expects files to be encoded in UTF-8.
Certain YAML features, including custom tags, are not as yet correctly rendered by PreviewYAML.
A YAML file containing
-.inf float values will prevent PreviewYAML from rendering the file, either as a preview or as a thumbnail. This issue is currently under investigation.
If you have found PreviewYaml to be useful, please consider writing a positive review on the Mac App Store, or simply give it a rating.
PreviewYaml makes use of code from the following sources:
You can view PreviewYaml’s source code at GitHub.