The through-line of the FDE role is taking a vague, messy business problem and breaking it into scoped technical work you can actually deliver under shifting constraints. Customers rarely hand you a spec. They hand you a frustration. Your job is to turn that into a plan.
Why this appears in interviews
FDE interviewers are explicit that they are not grading your final answer — they are watching how you think through a problem you have never seen before. They will give you a deliberately underspecified prompt and see whether you ask clarifying questions, state assumptions, and structure the problem, or whether you freeze or charge off building the wrong thing.
A repeatable decomposition method
- Clarify the goal. What outcome does the customer actually want, in their words? Restate it back. "So the real goal is fewer stalled tickets, not a CSV — is that right?"
- Surface constraints. What is fixed? Their cloud, their compliance rules, their existing systems, the timeline, the data they can share.
- State assumptions out loud. Where the spec is silent, make a reasonable assumption and say it. This lets the interviewer (or customer) correct you cheaply, before you build.
- Cut a thin first slice. Find the smallest piece that delivers visible value and tests the riskiest unknown. Ship that first.
- Sequence the rest. Lay out what comes after the slice and why in that order (usually: de-risk unknowns early, defer polish).
Working with incomplete information
You will never have full information, and waiting for it is itself a failure. The skill is making progress with reasonable assumptions, building something concrete to react to, and tightening as you learn. A rough working demo surfaces the real requirements faster than another meeting.
Ambiguity is not an obstacle to the work. Resolving ambiguity is the work.
A worked example
A customer says "make the agent faster." Decompose: faster where — retrieval, generation, or the whole round trip? (clarify). What is the latency budget and current number? (constraint). Assume the bottleneck is oversized context until measured (assumption). First slice: measure each stage and fix the worst one (thin slice). Then: caching, model choice, and parallelism in priority order (sequence).
Common interview mistakes
Charging off without clarifying. Spend the first minute narrowing the problem. It is the most-rewarded behaviour in the interview.
Over-scoping. Proposing a six-month platform when a two-week slice would prove the value reads as someone who has never had to ship under a deadline.
Key vocabulary
- Thin slice — the smallest deliverable that proves value and de-risks the biggest unknown.
- Assumption — a stated guess that fills a gap in the spec and invites correction.
- Scoping down — shrinking an ambiguous ask to something shippable now.