ACL2
Ranked 7 of 8 proof assistants by recommenders
Free theorem prover, used for industrial verification and recommended as a better fit than Dafny or Lean for reasoning about software. Critics say the user experience is hard to like.
Free theorem prover, used for industrial verification and recommended as a better fit than Dafny or Lean for reasoning about software. Critics say the user experience is hard to like.
6 people gave an opinion
- recommend it
- 6
- criticize it
- 0
- approval share
- 100%
Recommended in 5 of 13 months
- November 2025: recommended
- December 2025: recommended
- January 2026: not recommended
- February 2026: not recommended
- March 2026: recommended
- April 2026: not recommended
- May 2026: not recommended
- June 2026: not recommended
- July 2026: not recommended
- August 2026: recommended
- September 2026: not recommended
- October 2026: recommended
- November 2026: not recommended (month in progress)
Why it doesn’t carry the badge
- 6 people recommend itNeeds 10 or more, not met.
- Nobody criticizes itNeeds 2 to 1 or better, met.
- Recommended in 5 of 13 monthsNeeds 4 or more, met.
The same three rules apply to every product, and the badge can’t be bought. How the badge works
What people say about it
The reasons people give, with the number of comments that give each one. Open a reason to read what they said.
Why people recommend it
Each mark is one comment
Well suited to reasoning about software
“I hate the ACL2 user experience, but I think it is fundamentally more fit to reason about software.”
Comment from 22 Mar 2026 in “When AI Writes the Software, Who Verifies It?” “ACL2 might be a better fit in this regime than Dafny or Lean”
Comment from 23 Mar 2026 in “Formally Verifying the Easy Part” Powerful and capable prover
“The counterexample generator is very powerful because it leverages the knowledge base of the theorem prover”
Comment from 23 Mar 2026 in “Formally Verifying the Easy Part” “ACL2 is also VERY powerful and capable.”
Comment from 27 Nov 2025 in “Coq: The World's Best Macro Assembler? (2013) [pdf]”
What people warn about
Each mark is one comment
Hard user experience
“I hate the ACL2 user experience, but I think it is fundamentally more fit to reason about software.”
Comment from 22 Mar 2026 in “When AI Writes the Software, Who Verifies It?” Sometimes frustrating to use
“the both of these facts can sometimes be frustrating”
Comment from 2 Nov 2025 in “Why don't you use dependent types?”
Other proof assistants people recommend
The four most recommended other proof assistants, with the same counts for each, so you can compare like for like. The tick on each bar marks the 2 to 1 line the badge needs.
See all 8 proof assistants, rankedWhat people said
All 8 comments that mention it, newest first. Each links to the original comment.
“I’ve recently been enthralled with ACL2”
“As a good example of what Common LIsp can do in real life”
“The counterexample generator is very powerful because it leverages the knowledge base of the theorem prover”
“ACL2 might be a better fit in this regime than Dafny or Lean”
“I hate the ACL2 user experience, but I think it is fundamentally more fit to reason about software.”
“A lot of interesting industrial work has been done with ACL2 and related systems.”
“ACL2 is also VERY powerful and capable.”
“the both of these facts can sometimes be frustrating”
Counts come from 1,795,640 Hacker News comments, November 2025 to November 2026. How we count. Report a mistake.