Reporting bugs in TeX and friends

This web page is about reporting bugs in the original, unmodified, TeX and Metafont programs and the Computer Modern fonts, companion software, and the Computers & Typesetting books, all of which are maintained by their author, Donald Knuth.

In addition, new reports for the next tune-up and a few notable non-bug reports are listed separately.

Contents: submitting reports - research first - candidate software - CWEB(bin) - more \input - references.

Submitting reports for the 2021 TeX tune-up

There are two ways to submit reports, one public and one private:

  1. Send email to the public mailing list, This is preferred, since then many people have the opportunity to review the report, and often reply more quickly than I can.
  2. Send email to me,, if you want your report (name, email, contents) to be private. It is fine to do this if you prefer; much better than not reporting the bug at all.

Research before sending

Before sending: first, please do a general web search on your report before you send it in, choosing the relevant search terms, etc., to the best of your ability. Often bugs have already been found and fixed, or deemed not a bug.

Second, if the web doesn't have anything, please check Don's errata files (also distributed in TeX Live at texmf-dist/source/generic/knuth/errata). Try searching (e.g., grep) for keywords; it may not be easy to make your way through the errata files, but do the best you can. Hundreds of detailed bugs have already been reported.

Also, it is helpful to include printed page number references when possible, since that is how Don wants to receive them. It is also helpful to include line number references in the source files (*.web or *book.tex). The ideal would be to include both.

In all cases, what's of interest is true bugs in the code, typos or other outright errors in the text, etc. Requests for enhancements, new features, better explanations, etc., are not going to be reviewed by Don. However, if a report is in the gray area between bug and feature, please go ahead and send it, and we will review it.

Some enhancements, including but not limited to increasing array sizes and other configuration issues, can be (and have been) made in TeX Live and other implementations. So please also check the relevant documentation.

Software for which to send reports

Of course, the most important programs for which bug reports are solicited are TeX and Metafont themselves, and the Computer Modern fonts. In general, the contents of the Computers & Typesetting hardcover series:

Most of the other WEB programs released as part of the Stanford TeX project are also fair game, namely these:

dvitype gftodvi gftopk gftype mf mft pltotf
pooltype tangle tex tftopl vftovp vptovf weave

The main exception is BibTeX; reports for that are best sent to the public BibTeX mailing list ( Oren Patashnik, the BibTeX author and still maintainer, will see them there. Again, if privacy is a concern, you can send them to me and I will forward. (There are no particular deadlines or projected tuneup release dates for BibTeX.)

The other exceptions are patgen.web, pktype.web and pktogf.web. Reports for them should also be sent to or to me.


Don also still maintains the original CWEB programs written by him and Silvio Levy, and will accept bug reports for them. These are considered at the usual low priority and are not part of the TeX tune-ups; The Art of Computer Programming must take precedence.

With Don's agreement, as of 2019 the CWEB distributed in TeX Live is the cwebbin package, principally maintained by Andreas Scherer. Therefore, if you wish to report a bug in CWEB to Don, please be sure you are checking against the original CWEB distributed by Don and not the CWEB in TeX Live.

Reports for cwebbin should go to or the github project above. By the way, cwebbin is compatible with the original CWEB, while supporting more C and C++ language variants, has enhanced internationalization, etc.

More \input for testing

David Fuchs, Don's “right-hand man” for TeX, has created a custom toolchain to extensively test the original WEB files for range checks, memory management issues, and other such deep problems, beyond what is found by the trip and trap tests. Dave describes the background and discusses a couple of the bugs that have been found in the accompanying article published in TUGboat 41:1, pp.8–11 (PDF version).

Dave is on the lookout for plain TeX and Metafont documents, especially ones with devious macros and/or of notable length, that use only macro packages which work with unmodified TeX. Any help in this regard would be appreciated, and all appropriate credit will be given. Please send your documents, or ideas for such, to the (this private alias goes only to Dave and Karl).

Well-known TeX documents, such as The TeXbook and The Metafontbook sources, the result of applying weave to tex.web and mf.web, various free books, etc., have already been checked. What would be of most interest are personal documents that may test the limits of TeX (or any other Knuth-maintained program) in some way.

References and thanks

Don's previous tune-up reports were published in TUGboat:

Thanks to Barbara Beeton for giving us the great benefit of her experience in compiling all previous reports.

$Date: 2021/01/22 23:57:34 $;
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