live prototyping

Rehearse a 40-minute build with time reserved for testing. Choose a small user task, make it work and explain the failures you found before proposing a launch.

A worked live-round walkthrough. The trap is building a pretty summariser. The scoring path is a narrow extractor with structured output, a small test set that probes the hard cases, and an honest readout.

The part of the prototyping round that separates candidates. Ten minutes is enough for a small, sharp evaluation if you choose the cases well and grade them pass or fail.

Vague prompts are deliberate. The first five minutes show whether you can turn ambiguity into a buildable, testable scope, and the interviewer is watching that more than the code that follows.

Things break in live rounds, and interviewers often learn more from how you recover than from a smooth build. The answer is calm narration, a time box, simplification and a fallback that still shows judgment.

Agent prompts tempt candidates into ambitious builds that collapse. The strong answer builds the least autonomous version that demonstrates the idea, with mocked tools, clear limits and tests of the hard paths.

RAG is the most common live-build topic. Strong candidates choose the simplest approach that works for 30 documents, make citations real, and test retrieval and answers separately.

Asked of senior candidates who will run these rounds, and useful for anyone preparing. Knowing the rubric from the interviewer's side shows what to optimise for.

Progressive constraints test whether you can adapt under pressure without breaking what works. Principal-level candidates handle each constraint with the right mechanism, verify each change, and explain trade-offs.