# SWI-Prolog

Hacker Approved page: https://hackerapproved.com/p/swi-prolog/

15 people recommended SWI-Prolog in Hacker News comments, 1 had mixed feelings and 2 criticized it, November 2025 to October 2026. It was recommended in 6 of 12 months, in 11 threads. It meets the Hacker Approved badge rule.

**Verdict:** 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.

Summary written by Claude from 19 comments.

## Why people recommend it

- Actively maintained, approachable codebase (3 comments in the sample): "Amazing that it is still available & updated - even with its original name" ([source](https://news.ycombinator.com/item?id=46145714)) "its most popular implementation, that is also the best maintained" ([source](https://news.ycombinator.com/item?id=46646826)) "the SWI-Prolog codbase itself is quite approachable!" ([source](https://news.ycombinator.com/item?id=46642720))
- Flexible: server, browser and scripts (3 comments in the sample): "SWI-Prolog specifically provides a fairly straightforward JSON-based server mode "Machine Query Interface" ([source](https://news.ycombinator.com/item?id=45905248)) "you can even run it directly in your browser as there's a WASM port" ([source](https://news.ycombinator.com/item?id=47144316)) "invoke SWI-Prolog like you’d call any other language’s interpreter" ([source](https://news.ycombinator.com/item?id=46527030))
- Batteries-included with many libraries (2 comments in the sample): "SWI Prolog ships with libraries for Tries, Association Lists, Red-Black trees, and other things." ([source](https://news.ycombinator.com/item?id=48178856)) "SWI Prolog is just fine, and you'll find it to be batteries included unlike many other choices." ([source](https://news.ycombinator.com/item?id=46650037))
- Fast startup and good performance (2 comments in the sample): "The Prolog app is very fast, considering what it's doing, largely because it makes heavy use of tabling" ([source](https://news.ycombinator.com/item?id=48177139)) "It starts up quickly, and is decently performant within its peers of high level GC languages" ([source](https://news.ycombinator.com/item?id=45902978))

## What people warn about

- Less easy to use than alternatives (1 comment in the sample): "But it doesn't have the ease of use in my game dev context as a simple Dart library does." ([source](https://news.ycombinator.com/item?id=45907904))

## The badge

A product earns the Hacker Approved badge when at least 10 people recommend it, recommenders outnumber critics at least 2 to 1 (mixed feelings count toward neither side), it was recommended in at least 4 of the 12 months and in at least 5 different threads, and no single thread supplies more than half of the people who recommend it. Health and money products are never badged.

## Cite as

Hacker Approved, "SWI-Prolog", https://hackerapproved.com/p/swi-prolog/ (15 recommend, 1 mixed, 2 criticize; Hacker News comments, November 2025 to October 2026).

Counts updated 2 Nov 2026, with data through October 31, 2026.