Skip to content


Switch branches/tags

Name already in use

A tag already exists with the provided branch name. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Are you sure you want to create this branch?

Latest commit


Git stats


Failed to load latest commit information.
Latest commit message
Commit time
September 7, 2019 10:50
May 31, 2019 18:15
June 8, 2018 11:37
December 29, 2020 13:21
August 29, 2019 10:25

Web Prolog

Elevator pitch:

Imagine a dialect of Prolog with processes and mailboxes and send and receive – all the means necessary for powerful concurrent and distributed programming. Alternatively, think of it as a dialect of Erlang with logic variables, backtracking search and a built-in database of facts and rules – the means for logic programming, knowledge representation and reasoning. Also, think of it as a web logic programming language. This is what Web Prolog is all about.

This is a proof-of-concept demonstration/tutorial only. The system is not yet ready for online deployment. But you can install it locally, work through the tutorial, and play with lots of code examples.

Design and implementation by Torbjörn Lager, with a lot of help from Jan Wielemaker.

You may also want to have a look at SWISH ( which is a stable online IDE for Prolog, running 24/7 and having lots of users, especially among students taking CS courses involving logic programming and Prolog.

One of my long term goals is to replace the SWISH back-end with a Web Prolog node.


Get the latest SWI-Prolog

Install the latest SWI-Prolog development version.

Clone or download the repo

Running Web Prolog

From the web-prolog directory, do:

$ cd web-client
$ swipl

Now direct your browser to http://localhost:3060/apps/swish/index.html .

A book manuscript describing the approach is available at

It is very much a draft lacking some of the planned chapters, but should be readable enough for those who want to know more about the ideas behind Web Prolog.



A proof-of-concept SWI-Prolog implementation of Web Prolog







No releases published


No packages published