The FDE Case Interview: Structure the Ambiguity (C.A.S.E.)
The open-ended case is the hardest and least familiar round in the Forward Deployed Engineer loop, and the most common reason candidates are rejected is jumping to a solution before scoping the problem. A repeatable structure fixes that.
The C.A.S.E. framework
C.A.S.E. keeps you organized when you are handed something vague like "design a solution for this customer under these constraints." Narrate all four steps out loud — interviewers grade structured reasoning and customer awareness, not a single right answer.
Clarify
Pin down the requirements, users, data, and hard constraints (security, latency, offline) before touching a solution. State your assumptions with rough numbers.
Architect
Sketch the system at a high level — the boxes and arrows from data in to value out.
Solve
Go one level deeper on the core technical piece: the query, the pipeline, the retrieval step.
Evaluate
Name the trade-offs, risks, and how you would measure success. Running out of time before you reach Evaluate is the most common self-inflicted wound.
What separates a strong case answer
The grade is judgment under ambiguity. Offer two or three options with trade-offs and choose one for a stated reason — "I would pick B because of the compliance constraint" beats a perfect-sounding single answer. Timebox yourself: a few minutes clarifying, most of the time on architecture and the core solve, and always land on Evaluate.
Rung's Scenario Drills rehearse exactly these judgment calls — realistic customer situations where you make the call and get instant feedback on the reasoning.
Practice FDE scenario drills free
Practice FDE scenario drills free →Frequently asked questions
What is the FDE case interview?
An open-ended round where you are handed an ambiguous customer problem and asked to design a solution. It grades structured reasoning, stated assumptions, and the ability to scope a small end-to-end approach — not a single correct answer.
How do I structure an FDE case interview?
Use a repeatable structure like C.A.S.E.: Clarify the requirements and constraints, Architect the system at a high level, Solve the core technical piece in more depth, and Evaluate trade-offs, risks, and success metrics — narrating your thinking throughout.
What is the most common mistake in the FDE case round?
Jumping to a solution before scoping the problem. Clarify assumptions and constraints first, propose the smallest end-to-end approach, then iterate — rather than boiling the ocean.