Isabelle/HOL
Ranked 8 of 8 proof assistants by recommenders
Recommended for formal verification because its kernel is small and it has large libraries, and it is seen as a practical alternative to Lean. Critics find the tooling flawed and painful to use.
Recommended for formal verification because its kernel is small and it has large libraries, and it is seen as a practical alternative to Lean. Critics find the tooling flawed and painful to use.
6 people gave an opinion
- recommend it
- 5
- criticize it
- 1
- approval share
- 83%
Recommended in 5 of 13 months
- November 2025: recommended
- December 2025: not recommended
- January 2026: not recommended
- February 2026: recommended
- March 2026: not recommended
- April 2026: recommended
- May 2026: not recommended
- June 2026: not recommended
- July 2026: recommended
- August 2026: not recommended
- September 2026: not recommended
- October 2026: recommended
- November 2026: not recommended (month in progress)
Why it doesn’t carry the badge
- 5 people recommend itNeeds 10 or more, not met.
- 5 recommenders for every criticNeeds 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
Small kernel, large libraries
“HOL plus type classes and locales, backed by a small kernel and big libraries, will get you to production faster and with fewer regrets”
Comment from 2 Nov 2025 in “Why don't you use dependent types?” “Isabelle/HOL is probably at similar footing to Lean because its kernel is so simple.”
Comment from 19 Oct 2026 in “Lean now ships with verified kernels”
What people warn about
Each mark is one comment
Hard to use, far from nice
“Isabelle's better than Lean, but it's far from nice”
Comment from 30 Jul 2026 in “Are We Stuck with Lean?” “they're fine (if extraordinarily painful to use)”
Comment from 9 Sep 2026 in “C*: Unifying Programming and Verification in C (2025)” Tooling has deep flaws
“the tooling has deep flaws even outside the pure desktop-first app approach”
Comment from 27 Apr 2026 in “"Why not just use Lean?"” Fairly mediocre overall
“Isabelle proper is fairly mediocre”
Comment from 7 Feb 2026 in “First Proof”
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
6 of the 7 comments that mention it, newest first. Each links to the original comment.
“Isabelle/HOL is probably at similar footing to Lean because its kernel is so simple.”
“they're fine (if extraordinarily painful to use)”
“Isabelle's better than Lean, but it's far from nice”
“the tooling has deep flaws even outside the pure desktop-first app approach”
“Isabelle proper is fairly mediocre”
“HOL plus type classes and locales, backed by a small kernel and big libraries, will get you to production faster and with fewer regrets”
Counts come from 1,795,640 Hacker News comments, November 2025 to November 2026. How we count. Report a mistake.