That is not so easy to define, but roughly these are bugs:

• Inconsistencies between standards (both ISO and de-facto) and system behaviour.
• Inconsistency between documentation and system behaviour (which might be a bug in the documentation).
• Crashes. Any reproducible crash is worth reporting.

Non-experienced users are often surprised by how Prolog behaves. In the vast majority of cases this is not a bug. Use the forum to find answers.

What do I include in the bug-report?

Typically, a report must include the parts below to be meaningful. This is just a guideline, but if any of these parts are missing it is very likely that your report will not be answered at all or by additional questions.

1. The version of SWI-Prolog you use and the operating system.
2. A clear description on how to reproduce the issue. Typically, his consists of:
   • A complete program. Please do not send merely a fragment because
     1. It costs us a lot of time to complete and
     2. we typically complete it differently and the problem doesn't reproduce.

     Small programs are better, but it isn't always worthwhile to spend effort in creating a small program. If the program is big, do not include it in the first message, but merely describe that it is available and what it would take to obtain and run it.

   • The behavior you observe. If there are warnings or error messages, include at least the first couple of them literally.
   • The behavior you expected.

Where do I send my bug report

Preferably, bugs are reported using the GitHub issue tracker. Bugs raised there can be found by other users.

Alternatively, bugs can be sent by E-mail

See also

- Raise an issue at GitHub

- Old issues raised with Bugzilla

- Submit a patch

- "How to Report Bugs Effectively" by Simon Tatham, professional and free-software programmer