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A former CTO shares a simple coding screening question used to filter job applicants. The test presents basic code logic that qualified developers can solve mentally in seconds, while unqualified candidates resort to copy-pasting into interpreters or AI tools. The question includes a hidden character that produces different results when copy-pasted versus solved manually. Results showed 50% of applicants used automated tools, 47% answered correctly, and 3% answered incorrectly, effectively halving the candidate pool requiring deeper review.

I’m a former CTO. Here is the 15 sec coding test I used to instantly filter out 50% of unqualified applicants. – Jose Zarazua

Oh, nice one. One hidden sign and it checks two things:
<ol>
<li>If someone actually made the effort to solve it themselves (this really isn’t hard when you can interpret code in your head - takes a few seconds at best).</li>
<li>If someone at least has some attention to details (when pasting the code into an LLM or on a forum - either they notice the difference or not - it’s on them).</li>
</ol>
Got to remember to use those kind of tricks in my own recruitment strategies.

Kudos for remembering about aria-hidden, this way it has all the conditions met - fooling LLMs and still accessible for screen readers.

I find this incredibly dishonest, being afraid people are going to “cheat” by copying/pasting code does not excuse you trying to penalize them, what if they paste it into a code editor and edit the code. And every single software engineer worth their salt will copy/paste, this should not penalize them, it should be celebrated.
I agree we need to be able to prove that someone knows what they are doing, but at the end of the day we need to prove that they can get the job done, regardless of their method of doing so.
I’ve given programming tests for over 20 years to prospective engineers, I’ve never felt the need to try and trick them, it just makes me come off as an asshole.
Doing a programming test like this does prove something, but not what you think it does, it proves that you aren’t the type of CTO I’d want to work under in the first place.

Jokes on him. I am too lazy to copy paste the text so I just sent the AI a screenshot of the code. That gave me the correct answer.