PreviewJson

A tool to generate JSON QuickLook previews for macOS Catalina and above

Latest Release: 2.0.0

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How to Use PreviewJson

Install the app and run it. This will register the availability of the app’s QuickLook extensions, JSON Previewer and JSON Thumbnailer. You can now quit the app: just click OK:

To use QuickLook in Finder, select a JSON file — one with the extension .json — and press space. This will pop up a rendered preview of the file, either as pure data:

Or including JSON markers:

You will also see JSON 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 JSON Previewer and/or JSON Thumbnailer in System Preferences > Extensions.

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Customise the Preview

Click the settings icon in the main app. This allows you to adjust some of the key elements of the preview:

Presentation colours:
- Object keys.
- String values.
- TRUE, FALSE and NULL values if presented as text — or whether they are presented as graphics (solid or outline).
- JSON markers for objects ({ and }) and arrays ([ and ]), if shown.
The preview’s font and style.
The preview’s text size, from 10pt to 28pt.
The level of indentation (Small, Medium, Large or Extra Large), or whether previews are presented in tabulated fashion.
Whether previews should be displayed dark-on-light in macOS Dark Mode, or light-on-dark under macOS Light Mode.
Whether previews should include JSON markers for objects and arrays.
Whether previews should include raw JSON if rendering fails.

Choose your preferred text size using the slider, then pick the font you want the file to be presented in.

Choose your preferred JSON object key, string, true/false/null (if displayed in a text style rather than a solid or outline graphic) or JSON mark colour by selecting one of these items from the Colours: popup:

Now chose the colour by clicking on the colour well:

Select your preferred level indentation — Small, Medium, Large or Extra Large — from the JSON indent size pop-up. Alternatively, select Tablated from the same pop-up to have previews presented with keys and values, and array items arranged in tabular form.

The True/False/Null style: style selector allows you to choose to have these values presented as solid colour graphics, outline graphics or as text, respectively.

Click Apply 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.

Click Defaults to reset all preferences to their initial values — and then click Apply to retain the change.

Advanced Settings

The Advanced… button takes you to a selection of settings you can adjust more specialized preferences. These are items you are generally unlikely to need to adjust, including:

The initial size of the preview window: small, medium or large.
The width of the whitespace margin between preview content and the preview window, in points.
Whether the thumbnail icon colour style applied should match macOS’ mode, or always show light thumbnails. This is only available in macOS Tahoe and up.

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Feedback and Bug Reports

You can use the main app to submit feedback. Just click in the feedback icon in the main window, or select Report a Bug… from the Help menu:

Please include your email address if you would like a response. I can’t respond without one. Please see the privacy policy for details of email address usage.

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Troubleshooting

If PreviewJson reports that it was unable to render JSON, this is almost certainly caused by a malformation of the JSON itself. For this reason, you can optionally tell PreviewJson to display a file’s raw JSON in the event of a parsing error. This option is chosen in the Preferences panel and will allow you to QuickLook even bad JSON files, just without rendering.

Enjoyed Using PreviewJson?

If you have found PreviewJson to be useful, please consider writing a positive review on the Mac App Store, or simply give it a rating.

Thank you!

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Source Code

You can view PreviewJson’s source code at GitHub.

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Release Notes

2.0.0 10 April 2026
- Bring the UI into line with other second-generation PreviewApps.
- Rebuild the rendering engine from the ground up.
- Preview and thumbnail now respect the order of keys and values in the source file.
- Preview text is now selectable, and can be copied.
- The engine will make a stab at rendering bad JSON.
- Fully support macOS Tahoe.
- Migrate to Swift Concurrency.
- BREAKING Minimum macOS version is now macOS 12 Monterey.
1.1.4 13 April 2025
- Better Swift string and substring handling.
- Correct outlet ownership to mitigate reference cycle formation.
- Remove links to deprecated PreviewText and PreviewYaml.
1.1.3 30 August 2024
- Correctly render the bad JSON separator line: revert NSTextViews to TextKit 1 (previously bumped to 2 by Xcode).
- Improve true, false and null images.
- Improve preference change handling.
1.1.2 5 May 2024
- Revise thumbnailer to improve memory utilization and efficiency.
- Fix the ‘white flash’ seen on first presenting the What’s New sheet.
1.1.1 2 March 2024
- Correct indentation.
- Make tabulated preview optional.
- Fix for crashes caused by very deeply nested JSON files.
1.1.0 25 August 2023
- Allow the user to choose the colours of strings and special values (NaN, ±INF).
- New columnar layout.
1.0.4 12 May 2023
- Fix incorrect presentation of integers 1 and 0 as booleans (thanks, anonymous).
1.0.3 21 January 2023
- Add link to PreviewText.
- Better menu handling when panels are visible.
- Better app exit management.
1.0.2 14 December 2022
- Reduce thumbnail rendering load.
- Handle dark-to-light UI mode switches.
- Add App Store link.
1.0.1 4 October 2022
- Correct some text style discrepancies.
1.0.0 2 October 2022
- Initial public release.

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