Freedom251 › Formal Verification Tools
ACL2
What ACL2 is
ACL2 is a free, self-hosted interactive theorem prover for building formal models and proving properties about them. It uses ACL2 logic and a subset of applicative Common Lisp, combining a Lisp-based programming language with a reasoning engine. Its open-source Community Books provide lemma libraries, macros, proof-automation and debugging tools, interfaces, and hardware-verification libraries. The manual says ACL2 has been used to verify systems in academic and industrial settings; it supports counterexamples and proof artifacts. ACL2 runs on Linux, macOS, FreeBSD, and Windows. Documentation is available online, as local manuals, through an Emacs browser, and in the terminal with the :doc command. Installation requires a Common Lisp implementation, and some Community Books are guaranteed to work only with CCL or SBCL. The manual identifies version 8.7 as current and notes it lacks fixes and improvements made since March 2026. Building all Community Books can take hours and is usually unnecessary.
Who it suits
ACL2 suits people who need deductive verification of formal models and are prepared to install and work with a Common Lisp implementation. It also offers libraries and documentation for users exploring theorem proving or hardware verification.
What it does well
- Free and self-hosted.
- Runs on Linux, macOS, FreeBSD, and Windows.
- Community Books include proof and hardware-verification libraries.
- Documentation is available in several formats.
- Supports counterexamples and proof artifacts.
What to know first
- Requires a Common Lisp implementation.
- Some books are guaranteed only with CCL or SBCL.
- Version 8.7 lacks fixes and improvements since March 2026.
- Building all Community Books can take hours.
Getting started
- Visit the ACL2 website and choose the installation instructions for your operating system.
- Install a Common Lisp implementation.
- Follow the relevant instructions for Linux, macOS, FreeBSD or Windows.
- Install the ACL2 Community Books if needed; some books may require Quicklisp or a SAT solver.
- Use the online or local manuals, Emacs browser or terminal :doc command for documentation.
- Ask usage questions on the acl2-help mailing list; posting requires membership.
Verdict
ACL2 combines a theorem prover with libraries and documentation for formal verification across several operating systems. Check the Lisp prerequisite and version note before installing.
Questions
Is ACL2 free?
Yes. ACL2 is listed as free, with a free plan.
Which operating systems does ACL2 support?
Installation instructions cover Linux, macOS, FreeBSD and Windows. The Unix-like instructions include macOS with Intel or ARM processors.
Is ACL2 open source?
The ACL2 Community Books included with installations are open-source libraries.
What do I need to install ACL2?
Installation requires a Common Lisp implementation. Some Community Books are guaranteed to work only with CCL or SBCL.
Does ACL2 connect to other tools?
Community Books include tools for file input and output, operating-system access, raw Common Lisp libraries and connections to other programs.
Where can ACL2 users get help?
Users can ask usage questions on the acl2-help mailing list, which the manual recommends for new users. Posting requires membership; GitHub Issues are also available for reporting problems.
Facts from ACL2's own pages
- Build time
- The documentation says building all Community Books can take hours and is usually unnecessary. · acl2.org, 30 Sept 2026
- Community
- The ACL2 community page describes its user community as active and welcoming to new users, with GitHub Issues available for reporting problems. · acl2.org, 30 Sept 2026
- Community Books
- The Community Books include lemma libraries, macros, interfacing tools, proof automation and debugging tools, and specialty libraries such as hardware-verification libraries. · acl2.org, 30 Sept 2026
- Community libraries
- The ACL2 Community Books are open-source libraries that include lemma libraries, macros, interfacing tools, proof-automation and debugging tools, and hardware-verification libraries. · acl2.org, 29 Sept 2026
- Community support
- The acl2, acl2-help, and acl2-books mailing lists serve general discussion, user help, and discussion of developments in ACL2 and its Community Books. · acl2.org, 29 Sept 2026
- Development snapshot
- The page says development snapshots from GitHub are minimally tested and pre-built binary distributions are generally unavailable. · acl2.org, 30 Sept 2026
- Development version
- The installation instructions describe GitHub development snapshots as minimally tested and say prebuilt binaries are generally unavailable for them. · acl2.org, 29 Sept 2026
- Documentation
- Documentation is available online, as downloadable local manuals, through an Emacs browser, and at the ACL2 terminal with the :doc command. · acl2.org, 29 Sept 2026
- External dependency
- Some Community Books based on satlink and gl require an installed SAT solver, typically Glucose. · acl2.org, 30 Sept 2026
- Installation
- Unix-like installation instructions cover Linux, macOS with Intel or ARM processors, and FreeBSD; Windows has separate installation instructions. · acl2.org, 29 Sept 2026
- Integrations
- The Community Books include interfacing tools for file I/O, operating-system access, raw Common Lisp libraries, and connections to other programs. · acl2.org, 29 Sept 2026
- Lisp dependency
- Installing ACL2 requires a Common Lisp implementation, and some Community Books are guaranteed to work only with CCL or SBCL. · acl2.org, 30 Sept 2026
- Open source libraries
- ACL2 installations include the open-source ACL2 Community Books libraries. · acl2.org, 30 Sept 2026
- Operating systems
- The Unix-like installation instructions cover Linux, macOS, and FreeBSD; separate instructions are available for Windows. · acl2.org, 30 Sept 2026
- Prerequisite
- Installation instructions say users need a Common Lisp implementation, and note that some Community Books depend on Quicklisp and are only guaranteed to work with CCL or SBCL. · acl2.org, 29 Sept 2026
- Provenance
- The manual identifies ACL2 version 8.7 as copyright 2026 Regents of the University of Texas and authored by Matt Kaufmann and J Strother Moore. · acl2.org, 29 Sept 2026
- Purpose
- ACL2 combines a Lisp-based programming language for formal models with a reasoning engine that can prove properties about those models. · acl2.org, 30 Sept 2026
- Release
- The installation page identifies version 8.7 as the latest stable release and says it does not include improvements or fixes made since March 2026. · acl2.org, 30 Sept 2026
- Support
- ACL2 users can get help through the acl2-help mailing list, which the site recommends to new users. · acl2.org, 30 Sept 2026
- Use cases
- The manual says ACL2 has been used to formally verify systems in academia and industry. · acl2.org, 29 Sept 2026
Where ACL2 stands on Freedom251
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