Using MuPDF.js instead of pdf.js

iagogv · June 12, 2025

When viewing very large pdf files, or with heavy images, it would be great if Zotero used a light, efficient and fast PDF library such as MuPDF instead of pdf.js.

I know, you are not going to switch now, but let me just dream. This could go to a section "Ideas for someone forking Zotero and making a rewrite from scratch"

AdamSwanson1 · June 12, 2025

Agree that large file in Zotero is not really usable, especially when searching,

martynas_b · June 12, 2025

Please describe when exactly the Zotero reader feels slow — some issues might be fixable.

Also, what exactly is the problem with search?

iagogv · June 12, 2025

For example, I can see a difference in performance between pdf.js/Zotero and SumatraPDF reader (in Windows) for the PDF downloadable from https://annas-archive.org/md5/a9dd4adad6972ab77786d40dae5e6823 (if you want I share directly the file, let me know the way to do it), mainly when moving through the pages of the book (although current versions of pdf.js/Zotero improved a lot in performance; I even do not say current Zotero releases are slow)

iagogv · 2026-03-15T21:55:06+00:00

The images in the pdf of the paper https://www.cell.com/cancer-cell/abstract/S1535-6108(23)00441-5, are load much faster in Sumatra PDF (using library MuPDF) than in Zotero.

iagogv · 2026-03-15T22:05:19+00:00

BTW, regarding search, an example of pdf where Zotero reader is sometimes much slower than for example Sumatra is https://iris.who.int/server/api/core/bitstreams/9017d528-5692-49e2-85b0-51bea36e3409/content

iagogv · 2026-03-16T09:26:47+00:00

Try to search 'Hodgkin' (without quotes). Immediate in Sumatra, while keeps quite time searching (circular progress bar running) in Zotero

Vladimir Alexiev · 2026-03-16T14:30:48+00:00

@iagogv I use Sumatra but always thought it's written in C++ . Are you saying it uses a JS PDF reader library? Or MuPDF is in C++ but has JS bindings?

ridvanbinici · 2026-03-16T14:31:37+00:00

Do you make Zotero index whole pdfs with lots of characters and pages? Since I have set it to 1000 pages with 10000000 characters, it performs better in search. Also try to use apostrophes around the search term in order to prevent instant search, which makes Zotero freeze when trying to search for the part of the term (hod), instead of the full term Hodgkin is typed.

iagogv · 2026-03-16T14:40:58+00:00

@Vladimir Alexiev there is a JS library for MuPDF (https://mupdf.com/mupdf-js)

iagogv · 2026-03-16T14:43:12+00:00

@ridvanbinici I have tried indexing some pdfs, but I didn't get a real improvement. Regarding the suggestion, thanks for it, I didn't know about the use of apostrophes, but when I tested I tried not writing Hodgkin, but pasting the whole term.

emilianoeheyns · 2026-03-16T15:33:03+00:00

the mupdf js library uses wasm -- should be cross-platform without issue.

kuniipa · 2026-03-17T23:51:35+00:00

@ridvanbinici thank you for this tip!!!!