FDE · Interview Gym

The Decomposition Round, Simulated.

Every FDE interview guide describes this round and then tells you to find a human partner to rehearse with. Here it is instead. You get an open, real-world problem with no technical framing — and, exactly like the real round, you are scored on the clarifying questions you ask before you are allowed to propose anything. Then you decompose, prioritise, and say what you would not build. Four cases; an interviewer verdict at the end. This is the round Palantir is famous for and the one that most often decides an FDE loop.

pick a case · 5 clarifying questions · decompose & prioritise · name your cuts · get scored
decomposition round

An open, non-coding problem. Tests whether you can be dropped into a customer’s vague ask, alone, and come back with a scoped plan.

scope before solve

The behaviour being measured. Architecture in minute two is the single most common way to fail.

the cut list

What you explicitly will not build, and why. Strong candidates volunteer it; weak ones expand scope to look ambitious.

the constraint flip

Interviewers change a premise late on purpose, to check whether your plan was reasoned or memorised.

decomposition-round.session
InterviewerPick a case to begin.
Phase 0 · choose a case
The real round runs about an hour. Here it runs in three phases. In phase 1 you may only ask questions — the solution button is disabled until you have asked five, because that constraint is the lesson.
0
questions
0
score
1/3
phase

What this round is actually measuring

It is not a systems-design round with the diagram removed. The question behind every decomposition round is narrower and harsher: can we drop this person at a customer, alone, with a vague problem and a hostile network, and will they come back with something sensible?

01

Do you scope before you solve?

Strong candidates spend their first five minutes on who the user is, what decision changes, and what “better” measures. Weak candidates propose a pipeline. There is no recovery from the second one, because it is a direct sample of how you would behave in week one of a deployment.

02

Do you find the real constraint?

Almost every real customer problem is gated on data access, ownership, legality, or a person who does not want the project to succeed. A plan that assumes clean, complete, accessible data is a plan that has never met an enterprise.

03

Can you prioritise, out loud, with a reason?

A flat list of six workstreams scores near zero. “I would do B first, because without it A cannot be measured, and C is cheap enough to defer” scores highly — even if the interviewer disagrees with the ordering.

04

Will you say no?

Naming what you will not build is the clearest single signal of judgement available in an interview. It is also the behaviour that saves real deployments, which is why it is scored so heavily.

05

Do you adapt when a premise changes?

Interviewers routinely remove a constraint late — “actually, you cannot have that data”. Defending the original plan after its foundation is gone is a fail. Re-planning cheerfully is a strong pass.

The minute-by-minute shape

A real sixty-minute round has a recognisable rhythm. Knowing it keeps you from spending forty minutes in one phase.

// the shape of a strong decomposition round 00–05 who is the user? what decision changes? what does "better" measure? 05–12 what data exists, who owns it, what is legally usable, what is the timeline? 12–25 decompose → 3–4 independent sub-problems, ordered, with reasons 25–40 depth on ONE: approach, failure modes, how you would know it worked 40–50 the cut list: what you are not building, and the week-one assumptions to test 50–60 constraint flip → re-plan out loud, cheerfully

Notice that the first twelve minutes contain no proposal at all. Candidates find this uncomfortable and rush it; interviewers are explicitly watching for whether you can tolerate that discomfort, because a customer conversation feels exactly the same.

first proposal
≥ 12 min
sub-problems
3–4
depth on
exactly 1
cut list
volunteered

Check yourself

You are given “improve 911 response times”. What is the strongest first move?

Twenty minutes in, the interviewer says: “Actually, you cannot have access to the dispatch logs.” What do you do?

Which ending scores highest?

Common questions

What is the decomposition round in an FDE interview?

An open, non-coding problem — analysing a city’s taxi data, improving emergency response times, unifying fraud signals. You are scored primarily on the clarifying questions you ask before proposing anything, then on decomposing the problem into prioritised sub-problems, going one level deep on the first, and stating explicitly what you would not build.

How do you pass a decomposition round?

Spend the first five minutes on questions rather than architecture. Establish constraints — what data exists, who owns it, what is legally usable. Decompose into independent sub-problems and say which you would attack first and why. Go one level deep on that one. End by naming what you are explicitly not building and the assumptions you would test in week one.

Which companies use a decomposition round?

Palantir’s forward deployed software engineer loop is the best-known user and the round it is named for. The same archetype appears as case and scenario rounds at OpenAI, Anthropic and other companies hiring forward deployed and applied AI engineers, because it tests the thing all of them care about: can this person be left alone with a customer’s ambiguous problem.

What is the most common way to fail?

Proposing a solution before scoping the problem. Conventional interview preparation trains exactly that reflex, which is why strong algorithm candidates fail this round. Silence is the second most common failure — an interviewer can only score reasoning they can hear, so narrate continuously, including the dead ends.

Is this simulator the real round?

No — a real round is a live conversation with a human who probes and flips constraints. This drills the two things you can practise alone: which questions are worth asking, and the discipline of not proposing until you have asked them. Do it four times, then find a person for the conversational half.

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