I bet there are plenty of good extensions for Quick Look not everybody is aware of. I’d personally still love something that works for eps in Sequoia.
Here’s one I have come to rely on a lot.
Glance, free on MAS — for .cpp, Python, Jupyter Notebooks, markdown, tar/zip/gzip
I find Pacifist to be incredibly useful, letting me glance inside compressed archives without opening them up to see if there’s anything hinky about them, then opening only part of them if I want to. I’m normally a cheapskate and gravitate toward free software, but I think it’s worth $20, security-wise.
https://www.quicklookplugins.com is a site that lists QuickLook extensions, but it doesn’t really do a great job of identifying what’s up-to-date and what’s broken on older or newer versions of MacOS. If anyone’s got a better compilation, I’m all ears; I think QuickLook extensions are an incredibly useful and often-overlooked feature of MacOS.
I used to like QuicklookStephen. It lets you view text (true text, not TextEdit …rtf).
But it hasn’t worked properly since Catalina, due to changes in macOS. Now it only works for files with no extension. For example, it won’t work on something.conf.
The reason is that QLStephen sets itself as a default handler, but now if a file type (.xxx) isn’t registered, macOS makes up some random “dynamic” UTI, and it doesn’t fall to QLStephen. Or something like that.
So the irony here is that there’s a Windows Quicklook clone that works better than the macOS version, at least for text files.
I’m a fan of Suspicious Package for inspecting installer files before opening.
I use several Quick Look extensions that I find extremely useful…
Peek has been well worth whatever I pad for it. Provides attractive and functional Quick Look previews for 530 file types.
Apparency gives a great overview of key app info when using Quick Look on an application (and Apparency as an app is generally useful for inspecting
Mothers Ruin Software | Apparency
Suspicious Package is from the same developer as Apparency, and like @bb1 it’s excellent for inspecting installer files and where they are going to dump things before opening them. The full app is also very useful for getting more information and extracting individual items from installer packages.
Mothers Ruin Software | Suspicious Package
BetterZip makes it easy to look at the contents of compressed archives (the Quick Look extension works without paying for the full app if you don’t need its features).
A bit of a niche one here, but I have Worpertinger installed which is an app that converts old WordPerfect for Mac documents to other formats. It also includes Quick Look and Spotlight extensions that integrate WordPerfect documents into MacOS. I also have WPMacApp installed which I believe has the same extensions. Unfortunately they currently don’t work in MacOS 15 Sequoia, but will hopefully get updated to do so soon.
I’ll second your vote for Suspicious Package and BetterZip as well as Pacifist mentioned upthread. The curious thing is when I looked in the QuickLook folders within the various Library folders I didn’t find plugins for any of these apps even though the apps are installed. Are those plugins residing only within the app bundles and then just registered with the system? Suspicious Package is listed in the Extensions area of System Settings, but no sign of the other two. I don’t recall now, but those three apps might be drag-installed.
I once had a good half dozen or more third-party QL extension files and now I find only one, for Dropbox—with a ridiculous 1979 modify date. Yet I seem to be able to quicklook all the filetypes I’ve viewed in the past and perhaps more. It seems the native QL functionality has incorporated more filetypes over time while reducing the need for third-party solutions.
Looks great. Bought!
Not sure of the best way to figure out which apps provide them. I’ll add here if I figure it out.
Here are the loose ones I have installed.
and I have disabled (zipped)
Oldest dates back to 2007.
I should really have a cleanup.
I’m still on Sonoma
Are there any good solutions for previewing FLV videos with Quick Look? I have a bunch of old YouTube videos and digital microscopy videos that worked fine with Quick Look before Apple deprecated a lot of old QuickTime functionality.
I know that QLVideo will show static image previews of FLV videos, but I’m interested in previewing the actual video in the Finder without opening a separate app. Of course, I could convert the videos to a different format and then use Quick Look, but I’d rather not mess around with that.
(edited for clarity)
A lot has changed with how Quick Look generators and extensions work, and where things get saved. Howard Oakley has all the gory details.
Always give VLC a try. It plays almost everything. FLV (Flash Video) is on its list of features.
A consequence of this is that users can no longer control the priority of QuickLook plugins by which folder they’re in.
For example: Pacifist provides a QuickLook plugin for installer packages (.pkg). It can also interpret .zip files. I also used to have BetterZip installed, but only for its QuickLook plugin.
I liked the BetterZip display of .zip files better than Pacifist’s, so I moved the Pacifist plugin to /Library/QuickLook, and left the BetterZip plugin in ~/Library/QuickLook. macOS looked to the user Library version first.
(Since then the Pacifist plugin improved, so it is no longer an issue in this particular case.)
In the past few years, Apple deprecated Quick Look plugins (the .qlgenerator files) and with MacOS 15 Sequoia removed support completely. The approved (only) way now is to extend Quick Look using an ‘App Extension’ which is contained within an application’s bundle (i.e. the .app file). All explained in the Howard Oakley article @Simon linked to.
Howard Oakley’s article includes a link to his Mints utility which he’s updated so it can show you all the filetypes claimed by Quick Look extensions and which extension has claimed them.
As I say, if you’re on Sequoia those loose .qlgenerator files won’t be doing anything anymore. No longer supported. 
The authors of some may have updated them with an app that provides the functionality as a Quick Look app extension.
I’m pretty sure @josehill is looking for an extension that will play FLV files in Quick Look (like when you Quick Look an MP4 video), not an app that can open and play FLV.
Thanks. I do use VLC and think it is excellent. However, as @jzw suggested, I was looking for a Quick Look extension to preview FLV videos, not a full app.
The use case is opening a folder full of FLV video files in the Finder list view and then keying down the list to preview the videos in the Finder without opening them separately in an app. IIRC, Perian used to enable this, though maybe it was another tool.
Apologies for not being clearer with my original question. I’ll go back and edit it accordingly.
I’m on Sonoma, no plans to “upgrade”
Here’s the output of Mints on my machine:
~2500 lines https://pastebin.com/raw/PSpuMWn6
~1750 unique definitions https://pastebin.com/raw/mnWNf0Kc
As I say I’m on Sonoma with no plans to upgrade this year. I tend to update every 2 years. So I’m good with these esoteric QuickLook generators for a while.
That answers your earlier questions:
public.folder 👉 /Applications/Folder Preview.app/Contents/PlugIns/Folder Preview Extension.appex
Presumably this app is providing Quick Look for folders on your system (this is a useful find, I’ve installed it!):
com.google.webp 👉 /Applications/WebPViewer.app/Contents/Library/QuickLook/WebPQL.qlgenerator (1)
[…]
public.webp 👉 /Applications/CodeKit.app/Contents/Library/QuickLook/QLWebP.qlgenerator (1)
Presumably these two apps are the ones providing WebP Quick Look, though which one is taking charge when you Quick Look a webp file depends on what UTIs are assigned to those files on your Mac:
I don’t even use CodeKit, I just have it installed for QuickLook purposes 