QL Provider Inspector Help

Obscure Essentials

Copyright © 2026 Dr. Sascha Losko — Obscure Essentials. All Rights Reserved.

Contents

• How to inspect a file
• Using the report
• Quick Look providers explained
• How matching works
• Default apps
• Dynamic UTIs
• Optional Applications folder access (App Sandbox)
• Limitations and ambiguity
• Privacy

How to inspect a file

1. Choose File → Open…, Open Recent, or drag a file onto the app’s Dock icon.
2. The report appears in the window.
3. Use Copy Report to copy the full text report, or select text directly in any section and copy it.
4. Use Reveal to show the inspected item in Finder (if permitted).

When a file or folder is selected, macOS shows its native proxy icon in the window title bar. You can Command-click the icon to see the path, or drag it to other apps.

Using the report

• Sections are collapsible. Click the disclosure triangle or Hide to keep your view focused.
• Switch between Tree and Graph views for UTI conformance.
• The file path row includes a Copy button and a Bookmark status indicator.
• Provider rows include an Info button to show registered UTIs (and a copy button for the full list).
• Reveal buttons are only enabled when the file/app is inside the sandbox or has a security-scoped bookmark.

Quick Look providers explained

Quick Look is the macOS system that creates previews (Space bar) and Finder thumbnails. Modern macOS versions use Quick Look extensions (app extensions) for previews and thumbnails. Older systems also used legacy generators (bundles ending in .qlgenerator).

Preview vs. Thumbnail

• Preview providers generate the large preview shown by Quick Look (Space bar).
• Thumbnail providers generate small images shown in Finder.

Legacy generators (.qlgenerator)

Some file types still rely on system-provided legacy generators (for example, plain text types). On newer macOS releases, third-party .qlgenerator plug-ins may be ignored in favor of app extensions.

How matching works

Providers usually advertise supported types via QLSupportedContentTypes in their extension’s Info.plist. The app builds the file’s UTI conformance information and then finds the most specific match. Because UTIs support multiple inheritance, the app shows two conceptual conformance views: physical (data vs directory) and functional (content / executable / archive).

Example (simplified)
UTI: public.jpeg

Physical conformance:
public.jpeg → public.image → public.data → public.item

Functional conformance:
public.jpeg → public.image → public.content → public.item

If a provider claims public.image, it can match JPEG,
but a provider claiming public.jpeg is more specific.

If multiple providers match equally well, the app marks the best match as ambiguous and lists all equal candidates. In such cases, macOS may choose any of them.

Default apps

The app shows the default viewer and editor for the file’s UTI as reported by LaunchServices. These can be different on purpose (for example, you might view a Pages document in a PDF viewer, but edit it in Pages).

Dynamic UTIs

If macOS can’t map a file to a known UTI, it creates a temporary dyn.* identifier. In that case, matching is less precise and the app will show a notice. Installing an app that declares the file type (or adding a proper UTI declaration) can improve results.

Optional Applications folder access (App Sandbox)

If you run this app with App Sandbox enabled (as required for the Mac App Store), the app may not be able to scan /Applications to discover extension bundles inside third-party apps.

Use the toolbar buttons Re-grant… and Remove to manage optional Applications-folder access.

• This stores a security-scoped bookmark for the Applications folder.
• The bookmark is stored locally in your sandbox container (UserDefaults) so you don’t have to grant it each launch.
• Granting access is optional; the app still works without it, but may miss providers shipped inside third-party apps.

Limitations and ambiguity

• The app reports candidates based on advertised UTIs. Some providers may not advertise all types they can handle.
• Some Quick Look behavior is internal to the system and not exposed via public APIs.
• Election state/tags may be unavailable when PlugInKit discovery is restricted in sandboxed builds.
• Legacy generator listings are best-effort. In sandboxed builds, discovery may be limited.

Privacy

QL Provider Inspector does not send any data over the network. It inspects the file you provide and reads local metadata and local extension Info.plists.

Tip: If you plan to distribute via the Mac App Store, keep App Sandbox enabled and use user-selected file access.

Feedback and bug reports

I appreciate feedback and bug reports. If something looks wrong or you have an idea to improve the app, please send an email to support@losko.de.