Category Theory for Programmers by Bartosz Milewski
Shares rank 14 of 15 online courses by recommenders
Recommended as an approachable intro to category theory aimed at programmers, available as a free blog series and YouTube lecture series.
5 people recommended Category Theory for Programmers by Bartosz Milewski in Hacker News comments and none criticized it, November 2025 to October 2026.
3 of the 5 people who recommend it commented in one thread, “Actegories”.
Summary written by Claude from 5 comments.
5 people gave an opinion
- recommend it
- 5
- mixed feelings
- 0
- warn against or regret it
- 0
The record
Recommended in 2 of 12 months
In 3 different threads.
- November 2025: not recommended
- December 2025: not recommended
- January 2026: not recommended
- February 2026: not recommended
- March 2026: not recommended
- April 2026: not recommended
- May 2026: recommended
- June 2026: not recommended
- July 2026: recommended
- August 2026: not recommended
- September 2026: not recommended
- October 2026: not recommended
Why it doesn’t carry the badge
- 5 people recommend itNeeds 10 or more, not met.
- Nobody criticizes itNeeds 2 to 1 or better, met.
- Recommended in 2 of 12 monthsNeeds 4 or more, not met.
- Recommended in 3 threadsNeeds 5 or more, not met.
- 3 of its 5 recommenders came from one threadNeeds half or less, not met.
The same rules apply to every product, and the badge can’t be bought. Mixed feelings count toward neither side. How the badge works
What people say about it
Reasons grouped from a sample of 5 of the 5 opinions about it, picked in proportion to how many people recommend it, have mixed feelings and criticize it. Each mark is one comment in the sample. Open a reason to read what they said.
Why people recommend it
Each mark is one comment
Approachable introduction to category theory
“an intro to and overview of category theory aimed at programmers”
Comment from 14 Jul 2026 in “Actegories” “it came across as an approachable intro to the math”
Comment from 18 May 2026 in “Profunctor Equipment in Haskell” Written specifically for programmers
“a blog series on CT specifically for programmers”
Comment from 4 Jul 2026 in “Applied Category Theory Course (2018)”
Other online courses people recommend
The four most recommended other online courses, 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.
| Product | Recommend | Mixed | Criticize | Approval | Months | Had for | Badge |
|---|---|---|---|---|---|---|---|
| Nand2Tetris | 26 | 2 | 3 | 90% | 10 | — | Approved |
| Math Academy | 25 | 8 | 1 | 96% | 11 | — | Approved |
| Neural Networks: Zero to Hero by Andrej Karpathy | 25 | 2 | 1 | 96% | 8 | — | Approved |
| CS336: Language Modeling from Scratch | 11 | 1 | 0 | 100% | 5 | — | Approved |
| Category Theory for Programmers by Bartosz MilewskiThis page | 5 | 0 | 0 | 100% | 2 | — | — |
Also compared with CS50 by Harvard.
What people said
All 5 opinions about it, newest first. Each links to the original comment.
“Watch his lecture series on YouTube.”
“All of it is really mind opening stuff, and fun!”
“an intro to and overview of category theory aimed at programmers”
“a blog series on CT specifically for programmers”
“it came across as an approachable intro to the math”
Counts come from 1,791,911 Hacker News comments labeled by Claude, November 2025 to October 2026, with data through October 31, 2026. Counts updated 2 Nov 2026. How we count. Report a mistake.