Kevlin Henney

advisor • consultant • father • he/him • human (very) • husband • programmer • keynote speaker • technologist • trainer • writer

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Last Notes

2026-10-26 13:33:03 UTC

I'll be in London (Wednesday 2026-11-11 18:30) talking about the history of data abstraction:
ADTs and CLU
At the heart and start of this was Barbara Liskov's work with the CLU language. In this talk we'll take a trip back to the mid-1970s to explore work led by Liskov in "Programming with Abstract Data Types" and "Abstraction Mechanism in CLU", taking in the context in which these ideas emerged and the long-term influences on program and language design.
https://www.meetup.com/papers-we-love-london/events/317046728/

2026-10-22 15:05:21 UTC

Wow, search has got so bad that I can Google the literal title of a blog post and its author, and the results will not include the link. Instead, different articles (or videos) by the same author that are topic adjacent are listed. Ironically, the AI Overview refers to and summarises the correct blog post... but fails to provide a link 🤦‍♂️
Adding more detail to the search, however, misguides the AI Overview, so it summarises the wrong piece (providing a link to it) #FFS

2026-10-21 13:59:24 UTC

Pro tip: If you're using AI to message someone and trying to make it personal, as if you had written it, don't. Just don't.
That you couldn't be bothered to write it tells the reader how much you actually care. Put some effort into what you do. The absence of care is a negative differentiator.

2026-10-12 08:40:26 UTC

New on the blog: The Boots Theory of Software Architecture
How misaligned priorities can impoverish development
https://kevlinhenney.medium.com/the-boots-theory-of-software-architecture-e18cf0fa5a1b

2026-10-05 13:05:48 UTC

What do you think is the most pointless recent addition to Android? And why is it Bubbles?

2026-09-21 07:34:28 UTC

Application development pro tip: Have tests — that are run — to ensure existing user configuration is preserved when new features are added.
(It's 2026. This has been a solved problem for decades.)

2026-09-03 16:48:32 UTC

The ability to delivery continuously is not an unconditional good. For some teams, the CI/CD term is cover for continuous patching/hacking.
While any continuous/iterative/incremental flow is a reflection of an exploratory approach that converges on what is needed and responds to change, with progressive improvements in understanding and quality, it does not mean having this apparent flow has this cause.
It could just be a continuous flow of workarounds, fixes, etc. rather than a virtue.

2026-08-21 09:39:37 UTC

Blogged: Streamline Your LinkedIn Experience With This One Weird Trick
"The post suffers from trying to be meaningful and important. We don't get the poster's own voice and thoughts; we get paragraphs of aspiring anodyne anonymity."
https://kevlinhenney.medium.com/streamline-your-linkedin-experience-with-this-one-weird-trick-041daa16777a
https://files.mastodon.social/media_attachments/files/117/132/831/188/866/626/original/0e904c287cb9be13.png

2026-08-18 08:46:01 UTC

Currently setting up a new phone. While the OS (Android in this case) has improved what gets transferred since I last did this, it seems it comes as a surprise to many apps that moving to a new phone is a thing.
The overall experience is an embarrassing muddle of thrown-together security theatre.
Before it got weaponised, there used to be a discipline that focused on user experience and, rather than enshittifying it, actually improve it.
It would be nice to have UX make a comeback.

2026-08-13 10:38:47 UTC

"Is our AI adoption strategy likely to deliver good results?"
"What was the goal of adoption?"
"To adopt AI."
"I don't rate your chances."

2026-08-06 16:58:36 UTC

There's a belief AI broke search. It was broken long before that, for both product sites and regular web search.
What broke search was not AI but greed.
Reminded of this just now when I looked up an author on Amazon. The author's name is unique, so should return an exact match. None of the result set was visible without scrolling, just 'sponsored' irrelevance.
Sponsorship is a euphemism for interfering with the user's intent for the sake of money.
This is search — and has been for a while.

2026-07-14 15:50:08 UTC

An 'eggcorn' is an incorrect but oddly appropriate substitution for a word (see my WordFriday definition: https://www.facebook.com/WordFriday/posts/596606817093946).
Over the years I've encountered some initialisms in software that have been expanded in a way that might be considered eggcornish, e.g., UML as Universal Markup Language (certainly reflecting the aspirations of some of overly vocal advocates) and BDD as Business-Driven Development.
What eggcorns or similar have you come across?
https://files.mastodon.social/media_attachments/files/116/919/103/880/504/779/original/3ff2f4b57ce95e70.png

2026-07-05 09:21:19 UTC

Either customer support chatbots are a complete waste of time or I have just been very unlucky over the last few years.
I have never had a useful interaction or resolution from one (except to pass me to a human being, and that normally takes quite some effort). In terms of organisational hostility, they seem even worse than dial-up menu systems. My experience has left me with the perception that they are complete garbage.
Has anyone had consistently (or any) positive experiences?

2026-06-14 08:45:10 UTC

- reply

@nprofile…hs8h Which 'original paper' did you have in mind?

2026-06-12 11:09:28 UTC

What named principles (e.g., information hiding, DRY, etc.) in software development do you find are often referred to but are commonly misunderstood (or are actually flawed)? I have a talk, Principle Misunderstandings, where I cover a few, but I'm planning to extend this to half- and full-day formats, so I'd be interested in what you find is commonly misunderstood.

2025-12-18 08:49:57 UTC

Tom Gauld captures enshittification in a nutshell
https://www.newscientist.com/article/2504665-tom-gauld-on-plans-for-an-exciting-new-technology/
https://files.mastodon.social/media_attachments/files/115/739/702/296/671/805/original/daff484412680d38.png

2025-12-09 22:05:03 UTC

A reminder: when displaying dates and times in apps, do just that. Display dates and times. Don't withhold information have from the user. Don't try to be clever.
Just saw an app tell me that a particular message was sent to me on Wednesday. Which Wednesday? In the time zone I am currently in, it's Wednesday. If the message was sent on Wednesday 3rd December, that is the information you give the user.
Even better, include the time. That way, people can more clearly see intervals and durations.

2025-12-08 22:08:09 UTC

- reply

@nprofile…32m9 The separation of roles and activities you describe seems problematic. QA and QC should be very close together and it should naturally be a responsibility of the tester role to improve the process. They are in an ideal position to do so.

2025-09-30 06:05:33 UTC

Blogged: Step Back
"Instead of trying harder, do the opposite. Take a break. Properly. Don't just switch to another screen to browse memes, graze cat pics, answer your email or catch up with notifications, messages and socials."
https://kevlinhenney.medium.com/step-back-39d9e005ed89
https://files.mastodon.social/media_attachments/files/115/291/738/360/989/366/original/b30787a01f06b844.png

2025-06-10 09:23:59 UTC

Watching a speaker apologise for any quirks in the code they're using in their slides.
"It was generated by AI."
Resisted the temptation to raise my hand and say, "You know you're allowed to edit generated code before committing it?"
Don't use LLMs to increase the unmanaged technical debt in the world. Software is supposed to be soft; It's not written in stone.

2025-04-17 05:28:15 UTC

- reply

@nprofile…49rv I 'love' the fact that's beyond column 80 😳

2025-04-11 15:03:31 UTC

It's 2025 and we live in a highly connected and fallible world. No, "Something went wrong" is not an acceptable error message.

2025-02-03 09:01:30 UTC

On the blog ► Restrict Mutability of State
When it is not necessary to change, it is necessary not to change
I've revived and extended an old article that was originally submitted to 97 Things Every Programmer Should Know. It wasn't included in the original book, but was included as part of the overflow volume created by Shirish Padalkar.
https://kevlinhenney.medium.com/1ac69d1ec5fe
https://files.mastodon.social/media_attachments/files/113/939/133/051/901/440/original/b165124fc20446d4.png

2025-01-14 11:35:13 UTC

Program with GUTs - Good Unit Tests
Join me online for this 2-hour masterclass on Tuesday, 28th January, 11:00-13:00 GMT
https://techcornwall.co.uk/training/program-with-guts-masterclass/
https://files.mastodon.social/media_attachments/files/113/826/495/593/009/143/original/19a938caca127c49.png

2024-11-27 13:23:46 UTC

PSA for those at the back who were otherwise distracted: test-first does not mean (and has never meant) write *all* your tests first.
This misunderstanding has lead to some curiously dysfunctional workflows and embarrassing pronouncements and publications, including an MSDN entry many years ago and the disappointingly disastrous second edition of Glenford Myers' The Art of Software Testing.

2024-07-14 09:43:32 UTC

One of the most common examples of where we can drop an imperative verb prefix on a method name is in testing.
Unless a framework — such as pytest — requires 'test', such a prefix serves no useful purpose. It qualifies as a noise word, simply repeated what we already know from annotations/attributes, context, etc.
Stepping away from the imperative mood frees up the name (and the developer) to focus on naming a test more in terms of intent and purpose than as a directed action.

2024-06-20 11:26:58 UTC

Are you and your team writing user stories... or are you writing product owner stories?
There's a significant difference: most users would disagree that many features that product management, marketing, shareholders, etc., want to put into a product are actually stories from the perspective of the user.

2024-04-30 12:01:31 UTC

As a human I want to be required to enter a default value in a field that shouldn't be present on an input form so that a developer doesn't have to change any code
https://files.mastodon.social/media_attachments/files/112/360/054/296/166/340/original/643a65430b5502dd.png

2022-12-06 08:57:59 UTC

As the term 'intelligence' is used in 'artificial intelligence', it is perhaps worth asking, what kind of intelligence do AI systems represent? Confident and detail focused, but naïve, easily misled and lacking in common sense, worldliness, situational awareness, fairness, imagination, empathy, emotional intelligence and social intelligence 🤔