prolog-reasoner
SWI-Prolog as a "logic calculator" for LLMs — available as an MCP server and a Python library. Eliminate the black box from LLM logical reasoning.
LLMs excel at natural language but struggle with formal logic. Prolog excels at logical reasoning but can't process natural language. prolog-reasoner bridges this gap by exposing SWI-Prolog execution to LLMs.
Does it help?
On the built-in 30-problem logic benchmark:
| Pipeline | Accuracy |
|---|---|
LLM-only (claude-sonnet-4-6) |
22/30 (73.3%) |
| LLM + prolog-reasoner | 27/30 (90.0%) |
The gap concentrates in constraint satisfaction and multi-step reasoning — the combinatorial territory LLMs are weak on and Prolog is strong on. Full breakdown below.
Why it works
LLMs pattern-match; Prolog actually searches and solves. When the LLM writes its problem down as Prolog, two things happen at once:
- Prolog handles the combinatorial work LLMs are weak on — constraint satisfaction, multi-step inference, exhaustive search.
- The reasoning exists as code you can read, re-run, and debug. When it goes wrong, you see the exact Prolog that failed and why.
