Why Quick Look Plugins Stopped Working on macOS Sequoia and Tahoe
Apple removed the old .qlgenerator plugin format in macOS 15 Sequoia, and it stayed removed through macOS 26 Tahoe. Here's exactly what that changed, which plugins got rebuilt, and how to check your own Mac.
By Ram Velmurugan · Founder & Lead Developer, 1dot.ai
.qlgenerator format. Apple removed support for that format in macOS 15 Sequoia and the change has stuck through macOS 26 Tahoe. It has to be rebuilt on Apple's newer App Extension architecture to work again, and some developers have done that already while others haven't. There is no setting to turn this back on.Editorial note: 1dot.ai is building Quick Folder Preview, a folder-first preview app for Mac mentioned briefly near the end of this guide. It is not available to download yet, only a waitlist, and it plays no role in the fixes below. Every Apple documentation reference, plugin status, and third-party claim was checked live in September 2026 against Apple's own developer site and each project's own GitHub repository; sources are listed near the bottom.
What Actually Broke
Apple's own macOS Sequoia 15 release notes state it plainly under the Quick Look section, Deprecations: "Support for deprecated Quick Look Generator plugins is being removed. To provide previews and thumbnails for your custom file types, migrate to Quick Look Preview Extension and Thumbnail Extension API." That single line, filed against internal bug reference 116791365, is the entire basis for every plugin that quietly stopped working after this update.
It shipped in macOS 15.0 Sequoia in 2024. It is not a beta-only change, a setting, or something that got walked back in a later point release. macOS 26 Tahoe, the version current as of this writing, still does not load a third-party .qlgenerator plugin, full stop.
Why Apple Made This Change
The old .qlgenerator format dates back to the original Quick Look framework, well before macOS 10.15 Catalina introduced the separate QuickLook Thumbnailing framework for thumbnails in 2019. Third-party generators were CFPlugIn bundles, installed into a Library/QuickLook folder, and loaded directly into quicklookd, the same background process handling every other preview on the system. That shared-process design meant one badly written or crashing plugin could degrade or take down Quick Look previews for every file type, not just its own.
App Extensions solve the reliability problem by construction. A Quick Look preview extension (built on the QLPreviewingController protocol) or a separate thumbnail extension runs in its own sandboxed process, inside the host app's bundle at Contents/PlugIns, rather than a shared system folder. One extension crashing no longer takes anything else down with it, and the OS can manage its lifecycle the same way it manages any other app extension.
.qlgenerator under /System/Library/QuickLook. That is a naming leftover on first-party, signed, system-level code, not evidence that the old plugin type still works. Only third-party .qlgenerator bundles from other developers are affected by the removal.Legacy Plugin vs Modern Extension
| Property | Legacy .qlgenerator | Modern App Extension |
|---|---|---|
| File format | .qlgenerator bundle (CFPlugIn) | .appex bundle (App Extension) |
| Install location | ~/Library/QuickLook or a system Library/QuickLook folder | Inside the host app, at Contents/PlugIns |
| Runs inside | The shared quicklookd process, alongside every other plugin | Its own sandboxed process, isolated from other extensions |
| Works on macOS 15 Sequoia or later | No | Yes |
| Shows up in System Settings > Extensions | No, never did | Yes |
| Discoverable with `qlmanage -m` | Was, before removal | Yes |
| Requires code signing to run at all | No (part of the problem) | Effectively yes, as part of the extension system |
Architecture details checked against Apple's own macOS Sequoia 15 release notes and developer documentation, September 2026.
Which Plugins Actually Died, and Which Got Rebuilt
This isn't uniform across every plugin. Some developers rebuilt on the new API well before the cutoff hit; others haven't touched their project in years and the removal simply finished it off. Here's the real status of the plugins people ask about most, checked directly against each project's own repository.
QLMarkdown
Developer sbarex rebuilt this Markdown previewer on the modern App Extension architecture and continues shipping updates in 2026, including Mermaid diagram rendering, KaTeX math, and syntax-highlighted code blocks. It installs cleanly through Homebrew (`brew install --cask qlmarkdown`) and is one of the clearest examples of a legacy plugin that made the jump successfully.
Rebuilt, actively maintainedSourceCodeSyntaxHighlight
The same developer's syntax-highlighting previewer for source code files was also migrated to the current API and states macOS 12 Monterey or later as its baseline, well ahead of the Sequoia cutoff. If you relied on an older code-preview plugin that has gone quiet, this is the direct, actively maintained replacement.
Rebuilt, actively maintainedQLStephen (the original)
QLStephen, the plugin that let Quick Look preview plain-text files with no extension, is probably the single most widely installed casualty of this change simply because of how many developers had it on their Mac for years. A GitHub issue asking the maintainer to rebuild it on the modern API has been open since October 16, 2025, with no pull request merged as of this writing. If you depended on it, treat it as discontinued rather than waiting on an update.
Not rebuilt, no fix from the maintainerQLStephenSwift and similar from-scratch rebuilds
Rather than wait on the original maintainers, other developers wrote fresh replacements targeting the same gaps from day one on the current architecture. QLStephenSwift (by MyCometG3) and PreviewText (by smittytone) both cover the same plain-text-without-extension case QLStephen used to. PreviewCode, from the same developer, covers source-code syntax highlighting. None of these carry any legacy-plugin baggage to begin with.
New, built only on the modern APIA community-maintained list, Oil3/List-of-modern-Quick-Look-extensions on GitHub, tracks roughly fifty extensions confirmed built on the current API, explicitly excluding anything still on the old .qlgenerator format. It's a faster way to check a specific file type than searching one plugin at a time.
How to Check Your Own Mac
There's no dialog box or crash report when this happens. A plugin just stops rendering.
qlmanage -m
This lists every generator and previewer macOS currently has registered. If a plugin you expect isn't in that output, or a file type it used to cover now shows a blank page or generic icon when you press Space, treat it as affected.
Takes about 10 secondsSystem Settings > General > Login Items & Extensions > Quick Look shows which modern extensions are currently enabled. It only ever listed App Extensions, never legacy plugins, so an empty or sparse list there doesn't confirm anything on its own. The Terminal command above is the more reliable check.
Fixing It
Search the plugin's name together with "app extension" or check its GitHub releases page for anything dated after late 2024, when the removal shipped. If the original developer rebuilt it, reinstalling the current version is usually enough. If they haven't and a from-scratch replacement exists for the same file type, such as the ones listed above for plain text and source code, install that instead of waiting.
If you'd rather stop tracking which of your individual plugins survived this transition one by one, an all-in-one previewer built on the current API from the beginning, such as Peek, Looq, or Unfold, covers Markdown, code, and archive previews in a single install and isn't exposed to this specific problem again.
This Isn't the Homebrew Cask Issue
.qlgenerator support is a platform-level API change that affects every plugin still built that way, regardless of how you installed it. Homebrew disabling a cask, Glance included, on September 1, 2026, is a separate policy about code-signing and notarization on one distribution channel. A plugin can fail either check, both, or neither. If you specifically installed something through Homebrew and its cask got disabled, read our full breakdown of that cutoff instead, since the fix is different.Where Quick Folder Preview Fits In
None of the plugins or extensions covered here preview folder or archive contents without extracting them first, the specific gap Quick Folder Preview is built to close. We're building it as a drag-and-drop, folder-first take on instant preview for Mac, aimed at macOS 11 and later on both Intel and Apple Silicon, and built on the current App Extension architecture from the start rather than anything this post describes as deprecated.
Sources & Further Reading
Apple's official deprecation notice: macOS Sequoia 15 Release Notes, Quick Look section.
Plugin architecture background: The Eclectic Light Company, How Sequoia has changed QuickLook and its thumbnails, Michael Tsai, Sequoia No Longer Supports QuickLook Generator Plug-ins.
QLStephen migration request, unresolved: whomwah/qlstephen, GitHub issue #143.
Rebuilt plugins: sbarex/QLMarkdown on GitHub, sbarex/SourceCodeSyntaxHighlight on GitHub.
Modern-extension tracking list: Oil3/List-of-modern-Quick-Look-extensions on GitHub.
Frequently Asked Questions
The Bottom Line
A Quick Look plugin that stopped working on its own, with no setting change on your end, almost always traces back to this one change: Apple removed the old .qlgenerator format in macOS 15 Sequoia, and macOS 26 Tahoe never brought it back. Some developers, sbarex included, rebuilt their plugins on the current API and kept working the whole time. Others, QLStephen's original maintainer among them, haven't, and a from-scratch replacement is the more reliable fix than waiting. Either way, checking with qlmanage -m takes ten seconds and tells you exactly where you stand before you install anything.
Looking for more Mac productivity guides? Read our full guide to previewing files on Mac without opening them, see our complete Quick Look troubleshooting guide if Quick Look itself is crashing or showing blank previews for reasons unrelated to a plugin, read about Homebrew's separate cask-notarization cutoff if that's what you actually hit, browse every 1dot.ai guide, or check Quick Folder Preview's product page for the waitlist.
Want Folder and Archive Previews Without Extracting?
Quick Folder Preview is in development: a drag-and-drop, folder-first take on instant preview for Mac, built on the current App Extension architecture. No price or release date set yet, just a waitlist.
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