HOL4
HOL4: A free, open-source choice for interactive higher-order logic proving. Ranked #20 of 35 in Formal Verification Tools by our editors (7.5/10); pricing: Free plan; best for higher-order logic proof assistance.
At a glance
- Editor score7.5 / 10
- PricingFree plan
- Best forHigher-order logic proof assistance
- Free planYes
- Paid fromFree
- Facts checked20 Sep 2026
Where it wins
- Interactive tactic-based theorem proving with built-in decision procedures
- Integrates external SMT and BDD engines
- Supports theory libraries, proof artifacts, and counterexample generation
Where it doesn't
- Platform support is limited to Windows and Linux
- Installation requires Standard ML compiler prerequisites
- The workflow is centered on Emacs-based interaction
Our verdict on HOL4
HOL4 is a free, open-source interactive theorem prover and proof assistant for higher-order logic. It is intended for researchers, educators, and engineers working on formal mathematics, programming-language semantics, and software or hardware verification. Its ML programming environment supports theorem construction and proof-tool development, while interactive tactics and built-in decision procedures help users develop formal theories and prove properties.
The feature set is suited to projects that need more than basic theorem proving. HOL4 includes theory and theorem library management, theory export to compiled ML files, property checking, execution support, and counterexample generation for failed propositional properties. External SMT and BDD engine integration adds further proof and decision-procedure options. This combination makes HOL4 a fit for users who want to manage reusable theories and inspect failed properties within a higher-order logic workflow.
HOL4 is self-hosted and distributed as free software rather than through commercial pricing plans, so it suits teams and individuals seeking an open-source formal verification environment. The published installation guidance documents Windows support and Standard ML compiler prerequisites, with Linux supported through Unix-oriented installation instructions. The Emacs-based interactive workflow will appeal to users comfortable with editor-centered proof development, while those seeking a broader verified platform footprint or a different interaction model should consider alternatives. Pick HOL4 for higher-order logic, theory management, and extensible proof tooling; look elsewhere if platform breadth or a non-Emacs workflow is the priority.
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HOL4 pricing
HOL4 fact sheet
| Free plan | Yes |
|---|---|
| Paid from | Free |
| Verification method | Not verified |
| Supported formalisms | Theorem-proving |
| Counterexamples | Yes |
| Proof artifacts | Yes |
| Input languages | HOL higher-order logic; Standard ML |
| Deployment | Self-hosted |
| Deployment | Self-hosted |
| Platforms | Windows, Linux |
| Support | Community, Docs |
| Built for | Small business, Mid-market, Enterprise (editorial estimate) |
| Pricing | Free plan |
| Website | hol-theorem-prover.org |
| Facts checked | 20 Sep 2026 |
Alternatives to HOL4
- IsabelleA free, open-source proof assistant for broad mathematical and systems verification.9.4
- RocqA free, kernel-checked theorem prover with dependent types, automation, and certified extraction.9.3
- PVSA broad, self-hosted environment for hybrid formal verification workflows.9.2
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Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026
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