This guide tracks 7 patterns (6 of them typically hard), 4 commonly reported questions, and a 5-round loop that usually runs 4-8 weeks.
Key patterns
Showing 3 of 7Common questions
Showing 3 of 4Interview process
Showing 1 of 5 roundsStart studying now, without an account
Every lesson below is a free public reading page. No sign-up, no install, and the worked examples run in the tab.
The Python behind Jane Street's top patterns
These lessons do not teach the patterns themselves. They teach the language mechanics each pattern is built from, which is the part you have to have in your hands before the pattern is worth practicing.
- Dynamic Programming (1D)Python11 min readRecursion: a function that calls itselfSolve a problem in terms of a smaller version of itself, with a base case to stop.
- Dynamic Programming (1D)Python20 min readProfiling, complexity & cachingFind the hot path, fix complexity, and memoize repeated work with lru_cache.
- Dynamic Programming (2D)Python24 min readThe cost you asked for is not the cost you gotCorrect output, wrong cost. Learn to read a body for the work it hides, and to count that work exactly rather than guess at it.
- Math & GeometryPython9 min readInts, floats & arithmeticDo math with integers and floats, including floor division and modulo.
- BFS (Breadth-First Search)Python10 min readDictionariesMap keys to values: read safely, assign, and merge dictionaries.
- BFS (Breadth-First Search)Python12 min readCounter, defaultdict & dequeReach for specialized collections: count with Counter, group with defaultdict, queue with deque.
How Jane Street judges you outside the code
The values and engineering norms the interviewers are calibrated against. Useful for the behavioral round, and useful for deciding which trade-off to argue for in the technical one.
Values they name
- Intellectual Curiosity - love of learning and puzzles
- Collaboration - work together, not in silos
- Rigor - precision and attention to detail
- Long-term Thinking - sustainable growth over quick wins
- Quantitative Excellence - math and probability are core
What they look for in behavioral rounds
- Demonstrate exceptional quantitative and mathematical ability
- Show love of puzzles, games, and probability
- Exhibit strong communication of complex ideas
- Display collaborative and ego-free attitude
- Show you can think quickly under pressure
How the team builds
- OCaml/functional programming for developers
- Quantitative trading at the core
- Mental math and estimation skills valued
- Mock trading rounds test real-time decision making
- Collaborative flat culture - no titles, open office
Primary stack
- OCaml
- Python
- C++
- Linux
- Low-latency systems
- Code review
- pair programming and collaborative development
- Deployment
- careful deployments for trading systems
- Documentation
- code should be self-documenting with clear interfaces
Reading the guide is the easy part. Jane Street will ask you to perform.
CodeSparring is a practice environment, not a question bank. You sit a full round against an AI interviewer, in an editor that runs your code, and you leave with a score and a specific next rep.
An interviewer that reacts
Carry one problem from clarifying questions through to working code while an AI interviewer responds to what you say and what you type, by voice or by text.
Code that actually runs
An editor in the page with a real runtime and real test cases. You run your solution and read the output, the same way you would in a shared editor on the day.
A scored round, not a vibe
Every session ends with a rubric covering problem solving, communication, and code quality, so you can see which part of the round is costing you the offer.
And 364 lessons you can read right now, free
The whole curriculum is public. Read the concept, run the worked example in the tab, and only sign in when you want the graded exercise at the end of a lesson.