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Skim vs MuPDF: catalog facts
Skim	MuPDF
Free Free and open source under the BSD licence.	Free Free and open source under the AGPL. Commercial licensing is sold separately.
macOS	Windows, macOS, Linux, Android, iOS, Command line
SyncTeX integration makes it the standard viewer for LaTeX work Annotation and snapshot tools designed for reading academic papers	Extremely fast and small, with accurate rendering The bundled mutool covers most scripted PDF manipulation
macOS only Notes are stored in Skim's own format unless explicitly embedded	The viewer interface is deliberately minimal and keyboard-driven Commercial use of the library needs a paid licence from Artifex
Downloadable app	Downloadable app
Open source	Open source
License: BSD-3-Clause	License: AGPL-3.0
Not stated if an account is needed	Not stated if an account is needed
Not stated if it works offline	Not stated if it works offline
Official website Full listing and sources Checked September 22, 2026	Official website Full listing and sources Checked September 22, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.