Online Prolog Compiler

Prolog (PROgrammation en LOGique) is a declarative logic-programming language created in 1972 at the University of Marseille. You describe facts and rules; the engine searches for proofs by unification and backtracking. Prolog is foundational to computational linguistics (Definite Clause Grammars were invented to describe natural languages), expert systems, and classical AI research.

SWI-Prolog's installer is hefty and the interactive REPL takes a moment to learn. A browser sandbox is a friction-free way to experiment with backtracking, unify two terms, or trace a search. SWI-compatible Prolog runs in the sandbox; you can write clauses and query them within seconds.

Expert systems and rule engines, natural-language parsing via DCGs (Definite Clause Grammars), constraint solvers, theorem provers, puzzle solvers (the classic Einstein/Zebra puzzle is a favourite teaching example), and database queries issued as Prolog goals (?-). The sandbox runs SWI-compatible Prolog.

Paste a fact or a rule, then a goal — for example likes(mary, food). likes(john, wine). likes(john, mary). ?- likes(mary, X). — and hit Run. The query's answers appear in stdout. The highlighter understands Prolog atoms, variables (capitalised identifiers), predicate syntax, and the :- operator that separates rule head from body.

An online Prolog compiler is a cloud-hosted editor and runtime that executes Prolog code directly in your browser — no SDK download, no interpreter install, no PATH configuration. Facts, rules, unification and backtracking run with genuine logic-programming semantics, not a simulation. Everything runs inside an isolated sandbox: stdout and stderr stream back to the output panel in seconds, autosave keeps your work between visits, and a shareable URL hands the exact snippet to a teammate or interviewer. It doubles as a free Prolog interpreter for one-off checks.

Working through Prolog exercises often spills into Python; the Online Python Compiler answers in the same zero-setup style. Run Prolog in the browser whenever an answer matters more than an environment — this page is a Prolog playground, a Prolog interpreter and a code runner in one tab. Need the same snippet in Julia? The Online Julia Compiler runs on the identical editor — paste, run, compare.

The workflow is deliberately short: paste or write Prolog code in the editor, hit Run (or press Ctrl+Enter), and read the output below. Query a knowledge base and step through the solutions the solver returns — exactly how logic coursework is taught. Because compilation and execution happen in the cloud, you get the same result whether you are on a laptop, a lab machine or a borrowed Chromebook.

You can validate the Racket side of your project instantly with the Online Racket Compiler. When you need more than one language, the full catalogue lives on the Online Compiler hub — every language runs on the same editor with the same instant output.

Swi-Prolog installs vary by OS; the browser runtime gives every student the same engine. A local setup buys you package managers, GUIs and long-running processes — useful for shipping products, overkill for verifying a snippet. This free online Prolog compiler handles the everyday case: paste code, run, read output, share the link.

You can validate the Racket side of your project instantly with the Online Racket Compiler. For practice across the whole catalogue, the free online compiler hub lists every language on one page.