SWI-Prolog
Hacker ApprovedProlog implementation in Developer tools
Recommended as a free, batteries-included Prolog that starts quickly and runs out of the box, though some find it less easy to use than alternatives.
Recommended as a free, batteries-included Prolog that starts quickly and runs out of the box, though some find it less easy to use than alternatives.
18 people gave an opinion
- recommend it
- 16
- criticize it
- 2
- approval share
- 89%
Recommended in 6 of 13 months
- November 2025: recommended
- December 2025: recommended
- January 2026: recommended
- February 2026: recommended
- March 2026: not recommended
- April 2026: recommended
- May 2026: recommended
- June 2026: not recommended
- July 2026: not recommended
- August 2026: not recommended
- September 2026: not recommended
- October 2026: not recommended
- November 2026: not recommended (month in progress)
Why it carries the badge
- 16 people recommend itNeeds 10 or more, met.
- 8 recommenders for every criticNeeds 2 to 1 or better, met.
- Recommended in 6 of 13 monthsNeeds 4 or more, met.
The same three rules apply to every product, and the badge can’t be bought. How the badge works
What people say about it
The reasons people give, with the number of comments that give each one. Open a reason to read what they said.
Why people recommend it
Each mark is one comment
Actively maintained, approachable codebase
“Amazing that it is still available & updated - even with its original name”
Comment from 4 Dec 2025 in “SWI-Prolog 10.0.0 Released” “its most popular implementation, that is also the best maintained”
Comment from 16 Jan 2026 in “My Gripes with Prolog” “the SWI-Prolog codbase itself is quite approachable!”
Comment from 16 Jan 2026 in “My Gripes with Prolog” Flexible: server, browser and scripts
“SWI-Prolog specifically provides a fairly straightforward JSON-based server mode "Machine Query Interface"”
Comment from 12 Nov 2025 in “Learn Prolog Now (2006)” “you can even run it directly in your browser as there's a WASM port”
Comment from 24 Feb 2026 in “Extending C with Prolog (1994)” “invoke SWI-Prolog like you'd call any other language's interpreter”
Comment from 7 Jan 2026 in “Stop Designing Languages. Write Libraries Instead (2016)” Batteries-included with many libraries
“SWI Prolog ships with libraries for Tries, Association Lists, Red-Black trees, and other things.”
Comment from 18 May 2026 in “Prolog Basics Explained with Pokémon” “SWI Prolog is just fine, and you'll find it to be batteries included unlike many other choices.”
Comment from 16 Jan 2026 in “My Gripes with Prolog” Fast startup and good performance
“The Prolog app is very fast, considering what it's doing, largely because it makes heavy use of tabling”
Comment from 18 May 2026 in “Prolog Coding Horror” “It starts up quickly, and is decently performant within its peers of high level GC languages”
Comment from 12 Nov 2025 in “Learn Prolog Now (2006)”
What people warn about
Each mark is one comment
Less easy to use than alternatives
“But it doesn't have the ease of use in my game dev context as a simple Dart library does.”
Comment from 12 Nov 2025 in “Learn Prolog Now (2006)”
What people said
19 of the 21 comments that mention it, newest first. Each links to the original comment.
“SWI Prolog ships with libraries for Tries, Association Lists, Red-Black trees, and other things.”
“For regular users, it was relatively easy to understand and change the facts.”
“The Prolog app is very fast, considering what it's doing, largely because it makes heavy use of tabling”
“still being saner than SWI Prolog and co.”
“SWI-Prolog and its myriad of frameworks (which includes a full blown GNU Emacs clone) work out of the box anywhere”
“you can even run it directly in your browser as there's a WASM port”
“The Prolog is pretty nice the way I can now specify predicates for MQTT topic paths”
“it helps to actually use a proper compiled Prolog implementation like SWI Prolog”
“SWI Prolog is just fine, and you'll find it to be batteries included unlike many other choices.”
“its most popular implementation, that is also the best maintained”
“That's because SWI isn't following ISO”
“the SWI-Prolog codbase itself is quite approachable!”
“a language that's designed to solve those sorts of problems? In 14 lines of code.”
“invoke SWI-Prolog like you'd call any other language's interpreter”
“Amazing that it is still available & updated - even with its original name”
“But it doesn't have the ease of use in my game dev context as a simple Dart library does.”
“SWI-Prolog specifically provides a fairly straightforward JSON-based server mode "Machine Query Interface"”
“It starts up quickly, and is decently performant within its peers of high level GC languages”
“you could reasonably write entire applications in SWI-Prolog”
Counts come from 1,795,640 Hacker News comments, November 2025 to November 2026. How we count. Report a mistake.