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

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If you have a remote position open, your challenge is not attracting the correct candidate, it’s filtering out the bad ones, because you’ll have hundreds or thousands of them.

This is my favorite technique:
Add a programming knockout question to the application process that is so simple to solve that only* unqualified developers will not do it manually.

Here’s the question:

result = 0
for x in [3,3,5]:
    if x >= 3:
        result = result - x
    else:
        result = result + x

What is result?

1	0
-11	-10

Reveal the answer

If you got 1, congratulations, you have wired your brain to easily interpret code.

If you got -11, you copy pasted it somewhere. The trick is that there’s a hidden equal sign in the conditional “if x > 3”

The logic of course is that for a good programmer it would be more of a hassle to copy, open an interpreter or ChatGPT, paste it, run it, then answer, than just run the code in their head.

I used a very similar question while I was CTO at MonetizeMore. Interesting things happened:

50% of candidates got the AI/Interpreter answer.

47% Answered the question correctly.

3% Answered incorrectly.

A few candidates resubmitted the application after getting the answer wrong (we didn’t tell them), one of those candidates was a great hire.

One candidate posted the incorrect question to a forum, and got an answer. So when subsequent candidates Googled the incorrect question, they got the wrong answer.

—

*I should say this method is not perfect, and you’ll get false negatives, but I see it more as doubling your ability to process candidates, or reducing in half your recruitment time.

**If you’re going to use this, make sure that you include aria-hidden=”true” to make screen readers for people with disabilities compatible with reading the intended code.

I’ll Review Your Hiring Process for $1 →

Limited to 5 spots

Comments

13 responses to “I’m a former CTO. Here is the 15 sec coding test I used to instantly filter out 50% of unqualified applicants.”

2025-12-17

Nick Scavuzzo

so crazy that chat gpt says this is -11.

Reply
1. 2025-12-18
  
  Drew Miller
  
  There is a hidden equal sign – ChatGPT correctly answers a different question from what the reader sees.
  
  Reply
2. 2025-12-18
  
  zhifeng
  
  because if you copy-paste it, it reveals:
  
  result = 0
  for x in [3,3,5]:
  if x >= 3:
  result = result – x
  else:
  result = result + x
  
  notice the if x>= 3 instead of if x > 3, it is an html trick to hide the =
  
  Reply
  1. 2025-12-18
    
    james s
    
    Whoa,
    that’s the coolest part of this article.
    
    Thanks for pointing it out.
    
    Reply
    1. 2026-01-02
      
      niklas k
      
      That is literally the only part of this article
      
      Reply
2025-12-17

Tobi

I got the right answer (or course), but was expecting some kind of indication of where the loop starts and ends 🙂

Reply
1. 2025-12-18
  
  Jose Zarazua
  
  Python is all about indentation! 🙂
  
  Reply
2025-12-18

Florian

This is weird when coming here via the HN RSS feed, because the RSS viewer clearly shows the “hidden” equal sign. I was questioning my sanity for a moment.

Reply
1. 2025-12-18
  
  Jose Zarazua
  
  Oh man! yep RSS feeds would mess this up
  
  Reply
2025-12-18

numa

tbh, equality is opaque

Reply
2025-12-18

Steve

I was so confused by this. Turns out using w3m to view this post, the equal sign is not hidden.

Reply
2025-12-23

Walter

I got 1. Funny thing, it wasn’t until after I finished that I realized I hadn’t even considered what language the code is in. That’s how simple the problem is .

Reply
2025-12-27

Vic Bolio

Slick. Why shouldn’t there be a fail-fast on tech interviews?

Reply