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Isabelle vs Proof General: catalog facts
Isabelle	Proof General
Best for: Researchers and students working on formal mathematical proofs and verification	Best for: Emacs users developing formal proofs with interactive theorem provers
Free Free to download for Linux, Windows and macOS.	Free Free and open source under GPL-3.0-or-later.
Windows, macOS, Linux	Windows, macOS, Linux
Long-established proof assistant with regular releases Bundled jEdit-based IDE with dark mode and screen reader support All 3 strengths for Isabelle Long-established proof assistant with regular releases Bundled jEdit-based IDE with dark mode and screen reader support Builds for Linux on Intel and ARM, Windows and macOS	Works within the Emacs editor Provides modes for several proof assistants All 3 strengths for Proof General Works within the Emacs editor Provides modes for several proof assistants Available through NonGNU ELPA and MELPA
Large projects need a lot of memory, up to 64 GB Steep learning curve for those new to formal proof	Requires GNU Emacs 25.2 or later
Downloadable app	Downloadable app
Not open source	Open source
License not stated	License: GPL-3.0-or-later
No account needed	Not stated if an account is needed
Offline features available	Not stated if it works offline
Official website Full listing and sources Sources for Isabelle cl.cam.ac.uk/research/hvg/Isabelle Catalog checked October 2, 2026	Official website Full listing and sources Sources for Proof General proofgeneral.github.io Catalog checked October 8, 2026

“Not stated” means we have not confirmed it. Features can vary by device and plan.