32-bitCheck & ArchiChect

32-bitCheck – checks installed apps, code bundles, command tools and more for those which are 32-bit

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32-bitCheck is a much better tool for checking which apps and other software are still 32-bit. Check the folders of your choosing, and can check just apps, or all bundles including plugins and other executable code. Generates text reports to help you prepare your Mac for macOS 10.14 later this year. Why waste time and effort using System Information? New version 1.8 can resize text and checks for updates automatically. See also ArchiChect below for simple drag-and-drop checking.
32-bitCheck 1.8 (El Capitan, Sierra, High Sierra, Mojave and Catalina)

ArchiChect – drag-and-drop check of executable code architecture, and whether 64-bit

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Drag and drop apps, other code bundles of any type, or command tools onto ArchiChect to see which architecture(s) they support. Shows clearly whether they are 32- or 64-bit, and for bundles checks all executable code inside them too. Simple, lightweight, clear answers, and text reports. New version 1.1 checks its own code integrity and links to this page.
ArchiChect 1.1 (Sierra, High Sierra and Mojave)

Known issues:

ArchiChect reports the results of two quite different types of assessment, and sometimes, particular in the case of old fat binary apps supporting both Intel and PowerPC architectures, the top checkboxes and the text results might appear conflicting. The top checkboxes report the overall assessment: if that says the app is 32-bit, trust it. The text is aimed particularly at discovering whether there are any 32-bit components within the app. It’s possible for a 32-bit fat binary to report that there are no 32-bit components detected; it’s still 32-bit though.

Support Pages:

32-bitCheck Support
ArchiChect Support

Articles:

How to find all your 32-bit apps: a non-buyer’s guide