I have taken the decision to end-of-life this product. While PreviewYaml will remain on sale for the foreseeable future, and its source code will continue to be made available, it will not receive further updates.
How to Use PreviewYaml
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:
Open the Preferences panel from the main app’s PreviewYaml menu. This allows you to adjust some of the key elements of the preview:
The colour of mapping keys.
The colour of string values.
The colour of special values, eg. NaN, ±INF.
The preview’s font and style.
The preview’s text size, from 10pt to 28pt.
The level of indentation.
Whether keys should be presented in alphabetical order.
Whether previews should be displayed dark-on-light even in macOS Dark Mode.
Whether previews should include raw YAML if rendering fails because the YAML was malformed.
Choose your preferred text size using the slider, then pick the monospace font you want the file to be presented in.
Choose your preferred key, string value or special value colour by clicking the Colours: popup and then use the colour well to choose the colour itself:
Click Save to apply your choices.
Changing these settings will affect previews straight away.
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.
Known Issues
Certain YAML features, including custom tags, are not as yet correctly rendered by PreviewYAML.