FDE Interview Prep — Diagnosis Scenarios, Customer Simulations, Case Studies

What an FDE Interview Measures
The Technical Round — a System Diagnosis Scenario
The Customer Simulation Round
The Case Study Round
How to Prepare — RPG Missions as Interview Practice
Last Advice — the Candidate Who Says "I Do Not Know" Well Gets the Offer
Practice by Doing

What an FDE Interview Measures

If the center of a regular software engineering interview is coding and system design, the center of an FDE interview is judgment in unfamiliar situations. What the public postings of Palantir, OpenAI, and Anthropic demand in common comes in two bundles: production-grade engineering, and communication in front of customers. So the interview is built to touch both at once.

Formats differ by company. This post does not transcribe any company's question bank; it is a preparation guide generalized backward from public job requirements into three representative formats: the technical diagnosis scenario, the customer simulation, and the case study. Whichever appears, they share one trait — what gets graded is the quality of the narrowing process more than the accuracy of the conclusion. On this point they are exactly like the system design interview.

The Technical Round — a System Diagnosis Scenario

The most distinctive round. Instead of an algorithm puzzle, you get something like this constructed example: "Since this morning, part of the API traffic at a customer site has been failing intermittently. I will share this environment on screen — please diagnose." Some companies hand you a live environment; others run it verbally, with the interviewer describing system state on request.

Three things get graded. First, order. Whether the reproduce-isolate-hypothesize-verify structure from the playbook in part 4 is in your body. The candidate who dives into logs at random and the candidate who opens with "first, let me check whether the symptom reproduces" separate at the first sentence. Second, the quality of questions. The interviewer doubles as the customer, and running on guesses instead of asking is itself a deduction. Third, thinking aloud. Keep externalizing what you are looking at and why. Reaching the answer in silence scores lower than rejecting your own wrong hypothesis out loud along the way.

The Customer Simulation Round

The interviewer plays a customer. A constructed example: "I own this adoption project on the business side. Three weeks in, I see nothing on screen. My team is saying we should drop this project. Explain yourself." What goes on trial is not technical knowledge but the entire muscle set from part 5.

The grading points are translation and expectation management. Do you separate facts out of emotionally loaded speech ("when you say nothing visible, which screen are we talking about, concretely?"), do you offer confirmed facts and a next report time instead of defense, do you convert jargon into the other side's language? And the balance of apology and responsibility — the candidate who only apologizes fails, and so does the one who only blames the system. There is exactly one way to practice: ask a colleague to play the customer and do it out loud. Answers prepared in writing evaporate the moment pressure lands.

The Case Study Round

Take-home or presentation: you receive a fictional customer situation and produce a plan. A constructed example: "A manufacturing customer wants equipment-data analysis on our platform. Design the PoC." What is being graded wholesale is the ability to plan from a blank page — the content of part 6.

The skeleton of a strong answer is fixed: define success criteria first, down to the number and the judge; put the data boundary and security review into week one of the schedule; cut scope aggressively; state failure conditions and the next step. The common trait of weak answers is a detailed technical architecture with no operational design. If it is a presentation, fewer slides with a one-page success criteria document at the center leaves the stronger impression.

How to Prepare — RPG Missions as Interview Practice

As a practice tool that serves all three rounds, this blog carries the FDE Career RPG. All 31 field missions start from reports like "it is slow" or "we cannot connect" and force a diagnosis under limited time, trust, and access — a miniature of the technical round. Three ways to use it.

Solve out loud. Before picking a choice, explain why, spoken as if in the real interview. That is thinking-aloud training as-is.
Rotate the roles. Solo Firefighter, Embedded, Pre-sales PoC, and Handover have different win conditions. The Pre-sales PoC role in particular overlaps with the case-study round's instincts.
Find gaps via domain levels. The domain where missions repeatedly stop you is the domain to reinforce before the interview. Fill its checklist with the FDE Curriculum Roadmap.

Last Advice — the Candidate Who Says "I Do Not Know" Well Gets the Offer

Every round of an FDE interview is designed so that something you do not know will appear — naturally, since unfamiliarity is the essence of the job. So the final grading item is calibration: drawing the boundary of your knowledge precisely, and in the unknown zone, reasoning from principles and proposing how to verify. Install this sentence structure: "I have not operated that part myself. Reasoning from principles, it should work like this — and here is how I would confirm it." It signals someone who will make fewer dangerous calls in the field, and that is exactly what the interviewer is looking for.

This post closes the FDE Complete Guide series. We came from the definition all the way to the interview — if you did not read in order, fill the gaps from the list below.

Practice by Doing

FDE Career RPG — 31 missions, 6 health-check scenarios, 4 roles, 8 domains. The training ground for this whole series.
FDE Curriculum Roadmap — the self-check checklist of 65 skills across 10 domains.

The FDE Complete Guide series