ACL2

Score6.6

Rank#8 of 33

Free planNo

Runs onLinux, macOS, Self-hosted, Windows

Summary

ACL2 is an interactive theorem prover that pairs a Lisp-based language for formal models with a reasoning engine to prove properties of those models. It has been used to formally verify systems in academic and industrial settings. Its open-source Community Books provide lemma libraries, macros, interfaces, proof automation, debugging tools, and hardware-verification libraries. Documentation is available online, as local manuals, through an Emacs browser, and at the terminal using the :doc command. Installation instructions cover Linux, macOS, FreeBSD, and Windows. ACL2 requires a Common Lisp implementation; some Community Books are guaranteed to work only with CCL or SBCL, while books based on satlink and gl require a SAT solver, typically Glucose. The manual identifies version 8.7 as the current release and notes it lacks fixes and improvements made since March 2026. GitHub development snapshots are minimally tested, and prebuilt binaries are generally unavailable. Building all Community Books can take hours and is usually unnecessary. ACL2 is free and self-hosted.

Who it is for

It suits people working with formal models and deductive theorem proving, including in academic or industrial verification. Users should be prepared to install a Common Lisp implementation and consult the documentation for library requirements.

What is good

Free and self-hosted.
Community Books include proof and debugging tools.
Documentation is available in several formats.
Supports Linux, macOS, FreeBSD, and Windows.

What to know first

Requires a Common Lisp implementation.
Some Community Books require CCL or SBCL.
Some books require a SAT solver.
Development snapshots are minimally tested.

Verdict

ACL2 provides a theorem-proving environment with extensive open-source libraries and documentation. Its Lisp prerequisite and the differing requirements of some Community Books are worth checking before installation.

Compared on formal verification tools

Free plan: Yesacl2.org
Verification method: deductiveacl2.org
Supported formalisms: theorem-provingacl2.org
Counterexamples: Yesacl2.org
Proof artifacts: Yesacl2.org
Input languages: ACL2 logic and a subset of applicative Common Lispacl2.org
Deployment: self-hostedacl2.org

Facts

Purpose: ACL2 is an interactive theorem prover combining a Lisp-based programming language for formal models with a reasoning engine that proves properties of those models.acl2.org · 29 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
Use cases: The manual says ACL2 has been used to formally verify systems in academia and industry.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
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
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
Release: The ACL2 manual identifies version 8.7 as the current release and says it is stable and well tested, while noting it lacks fixes and improvements made since March 2026.acl2.org · 29 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
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
Support: ACL2 users can ask usage questions on the acl2-help mailing list, which the manual recommends for new users; posting requires membership.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
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
Open source libraries: ACL2 installations include the open-source ACL2 Community Books libraries.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
Operating systems: The Unix-like installation instructions cover Linux, macOS, and FreeBSD; separate instructions are available for Windows.acl2.org · 30 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
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
External dependency: Some Community Books based on satlink and gl require an installed SAT solver, typically Glucose.acl2.org · 30 Sept 2026
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