PRACTICE GUIDE JANE STREET
Jane Street Quant Developer Practice Test
Jane Street does not publish the shape of its quant developer screen, and candidates describe it as 2 to 4 problems questions in 60 to 120 minutes, roughly 20 to 40 minutes per question, written in a code editor and run against tests you cannot see.
Those are ranges across firms running this format rather than Jane Street's own figures, so treat them as the shape to train against and check the instruction screen on the day for the marking rule.
Outcry is not affiliated with Jane Street and has no access to their assessment content. This guide describes an assessment format that candidates report publicly; the questions here are generated by Outcry and are not Jane Street’s own.
What it screens
A quantitative trading firm active across equities, ETFs, bonds, options and currencies, known for OCaml and a strong internship pipeline.
- ✓Reading concurrent code and pointing at the defective line
- ✓Order-book data structures: what happens on a cross, a cancel, a partial fill
- ✓Algorithmic complexity chosen for the input sizes stated in the problem
- ✓Monte Carlo methods and when a simulation beats a closed form
Where it sits at Jane Street
A quantitative trading firm active across equities, ETFs, bonds, options and currencies, known for OCaml and a strong internship pipeline. What that means for the screen is that the questions tend to be drawn from the work rather than from a textbook, so the format below is the shape to train against rather than a syllabus.
Candidates also report 3 other screens at Jane Street, covered separately on this site. Where a firm runs several, they usually sit in one round rather than spread across the process, so the pacing of the whole set matters more than any single section.
The format
Jane Street does not publish this screen's shape, and it varies between firms, so these are the ranges candidates report rather than exact figures.
| Questions | 2 to 4 problems |
|---|---|
| Time | 60 to 120 minutes |
| Per question | 20 to 40 minutes |
| Negative marking | No |
| Answer style | Code editor, run against hidden tests |
| Where it sits | First technical round, usually on HackerRank or CoderPad |
What it tests, with a worked example
Every example below is generated by Outcry, drawn from the same question generators the timed drills run. None of them is Jane Street’s.
Data structure implementation
Build the thing rather than call it: an order book, a cache, a ring buffer. Graded by hidden tests, so there is no partial credit for an approach.
Reading someone else's code
A diff or a function with a bug in it, and the question is where.
Example
A lock-free SPSC ring buffer publishes its head index with memory_order_relaxed. What can go wrong?
- The index can wrap incorrectly
- The consumer may see the new index before the slot's data is visible
- The producer may block
- Nothing - SPSC needs no ordering
Answer The consumer may see the new index before the slot's data is visible
The publishing store needs release semantics to pair with the consumer's acquire load, or the buffer write can be reordered after it.
Language and systems detail
Memory, references, undefined behaviour and the things that bite in production.
Example
What is the solution to T(n) = T(n/2) + n^2?
- Theta(log n)
- Theta(n^3 log n)
- Theta(n^3)
- Theta(n^2)
Answer Theta(n^2)
log_2(1) = 0 and the driving term is n^2. 2 beats 0, so the top-level work dominates and the answer is n^2.
Numerical and data handling
Floating point, aggregation and joins on data that does not fit the obvious shape.
Example
A price walks on the whole numbers 0 to N. Each step it moves +1 with probability p and -1 with probability 1 - p, independently. It stops the first time it touches 0 or N. N = 8 start = 4 p = 0.6 One question, six parts. Each part uses the part before it.
Part 3 of 6. Now use p = 0.6. What is the probability the walk stops at N?
Answer 0.8350515463917525
With drift the answer is (1 - r^start)/(1 - r^N) where r = (1-p)/p = 0.6667. That is (1 - 0.1975) / (1 - 0.039) = 0.8351. Part 1 gave 0.5, so the drift is worth 0.3351 here.
Edge cases
Empty input, one element, duplicates and overflow. The hidden tests always include them.
Probability behind the problem
Screens that look like coding questions and are really expectation questions.
Example
[ 2 2 1 ] [ -4 -4 -2 ] [ 2 2 1 ]
What is the rank of the matrix above?
- 3
- 0
- 2
- 1
Answer 1
Row reduction leaves 1 nonzero row, so the rank is 1. Rank is the number of independent rows, which is also the number of independent columns, and it is at most 3 for a 3x3.
What a good score looks like
Coding screens are usually pass-fail on hidden tests rather than scored, and candidates commonly report that a solution passing every correctness test still fails on a timeout. Treat full marks as solving every problem inside the complexity bound, not merely solving it.
How to train for it
- 01Implement the core structures from scratch once each. The screens ask you to build them, not use them.
- 02Write the edge cases into your own tests first. That is where the hidden ones live.
- 03Practise without an autocomplete. The screens run in a bare editor, and the gap between writing code with help and without it is larger than most people expect.
TRAIN IT HERE
The drills that match each section
Concurrency Clash
Find the data race, name the fix - real C++ defect patterns, five levels.
Order Book
Matching-engine mechanics: crosses, cancels and partial fills.
Algorithm Lab
DP tables, Monte Carlo estimation and speed rounds at four difficulty tiers.
SIT THE FULL BATTERY
All the sections back to back on one clock, marked the way the real screen marks them, with a by-skill breakdown at the end. Included with any pass.
Also reported at Jane Street
Common questions
- Is the Jane Street quant developer test multiple choice?
- Reported as code editor, run against hidden tests. Formats move, so treat this as the shape rather than a guarantee.
- How long is the Jane Street quant developer test?
- Candidates report 2 to 4 problems questions in 60 to 120 minutes, roughly 20 to 40 minutes per question.
- Is there negative marking on the Jane Street quant developer test?
- No. A wrong answer costs nothing beyond the mark you would have earned, so leaving an item blank is never better than guessing at it.
- How do I practise for it free?
- Every drill linked on this page is free to play, with no account, inside a daily run cap. Questions are generated fresh each run, so there is nothing to memorise between attempts.
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