CTO's 15-Second Code Challenge Traps Half of Dev Candidates Using AI

A CTO from Monetize More has revealed a rapid 15-second technical screening method that reportedly filters out 50% of developer candidates. The challenge presents a seemingly straightforward Python code snippet designed to test basic loop and conditional logic: result = 0; for x in [3, 3, 5]: if x > 3: result -= x else: result += x. The trick lies in a hidden, zero-width equal sign character (=) stealthily embedded within the code when displayed online. While invisible to the human eye, this hidden character is copied along with the code, causing issues when pasted into AI tools like ChatGPT or online interpreters. Such tools frequently misinterpret the code, leading to an incorrect answer, typically -11. Conversely, a manual trace reveals the correct output: starting with result = 0, the first two x=3 iterations increment result to 6, and the final x=5 iteration, where 5 > 3 is true, subtracts 5, yielding result = 1.

The CTO reported that 50% of candidates failed the test, primarily by providing the AI-generated -11 response, indicating an over-reliance on automated tools without critical verification. A significant 47% correctly identified 1, demonstrating manual code interpretation, while 3% gave other incorrect answers. This method, though acknowledged as not infallible, serves as an efficient initial filter. The revelation has sparked considerable debate within the tech community. While some laud it as an ingenious way to assess genuine coding acumen and critical thinking over blind AI reliance, others have condemned it as “ridiculous,” “unethical,” or even “illegal,” suggesting it unfairly mocks candidates. Concerns were also raised about candidate nervousness impacting performance or the potential for image prompt injection if screenshots were used as a workaround. Despite the controversy, the technique mirrors similar practices observed in academic settings to detect AI use in assignments, underscoring a growing challenge in assessing authentic skills in an AI-pervasive environment.