Jane Street Software Engineer mock interview

OCaml is NOT required (most hires don't know it). Mathematical thinking, probability, and Bayesian reasoning are valued. Super-Day onsite includes game-based rounds unique to Jane Street.

  • OA + Super-Day
    Format
  • NOT required
    OCaml
  • Game-based
    Unique rounds
  • Free
    First mock

Why Jane Street's interview is structurally different from FAANG and from Citadel/Two Sigma

Per Jane Street's official prep page (janestreet.com/preparing-for-a-software-engineering-interview), their engineering blog 'What a Jane Street dev interview is like,' and 2025 candidate reports, Jane Street's interview is built around mathematical thinking, not algorithmic optimization. The Super-Day onsite includes a game-based round unique to Jane Street: you play a real-time mathematical game (simplified auction, probability estimation, market-making sim) with the interviewer. The dimension graded is how you reason under uncertainty in real time — not whether you 'win' the game.

OCaml is famously NOT required. Jane Street explicitly discourages candidates from learning OCaml just for the interview: 'Please don't use OCaml just because you think it will make us happy.' Most hires don't know OCaml coming in. Use the language you're most comfortable with. The functional-style thinking they value (modular helper functions, clear decomposition) can be demonstrated in Python or any imperative language.

Background in competitive math/programming (Putnam, IMO, USACO, ICPC) is explicitly valued in resumes. Jane Street's culture values mathematical depth — candidates who can't engage with probability brainteasers, conditional probability, or expected value miss the dimension Jane Street grades most heavily. Compensation is comparable to Citadel ($300-450K first year, $800K-1.2M at 5 years for standard performers) — above FAANG but with high performance filtering.

What the loop looks like

Round-by-round

  1. 01

    Application + recruiter screen

    Pre-onsite
    30 min

    Background, mathematical/coding interests, motivation. Putnam, IMO, USACO, ICPC results valued in resume.

  2. 02

    Online coding assessment

    Pre-onsite
    60 min

    Core gating step. Algorithmic problems graded on correctness AND functional-style design (modular helper functions). Use any language you're most comfortable with.

  3. 03

    Technical phone interviews × 1-2

    Pre-onsite
    60 min each

    Live, collaborative sessions over video call or shared editor. Problem-solving depth + clear communication graded equally.

  4. 04

    Super-Day onsite — technical

    Onsite
    Multiple 60-min sessions

    In-person or virtual. Coding, system design, deeper algorithmic problems. Functional-style thinking graded across rounds.

  5. 05

    Super-Day onsite — behavioral

    Onsite
    60 min

    Cultural fit, intellectual curiosity, mathematical thinking. Jane Street culture values intellectual depth over conventional 'leadership stories.'

  6. 06

    Super-Day onsite — game-based round (UNIQUE)

    Onsite
    60-90 min

    Mathematical games / probability puzzles. Tests how you reason under uncertainty in real time. Practice probability and game theory before the loop.

Question bank

Real interview questions reported by candidates

  • Coding

    "Implement a function in functional style. Write small modular helper functions to show clear thinking. Use Python (or any language); no need to attempt OCaml."

    Source · janestreet.com/preparing-for-a-software-engineering-interview official, blog.janestreet.com 'What a Jane Street dev interview is like'
  • Coding

    "Algorithm problem with mathematical flavor: graph coloring with constraints, optimization on a probability tree, etc. Functional-style decomposition expected."

    Source · interviewquery.com Jane Street SWE 2025, everythingquant.com Jane Street guide
  • Coding pattern

    "Probability brainteaser: 'You roll dice until you see a 6. What's the expected number of rolls?' or similar. Bayesian reasoning, conditional probability, expected value."

    Source · interviewing.io Jane Street questions, myntbit.com Jane Street quant 2026
  • Coding pattern

    "Game-based round: play a real-time mathematical game (auction, simplified market making, probability estimation). Tests how you reason under uncertainty live."

    Source · algo.monster Jane Street guide, blog.janestreet.com dev interview
  • System design

    "System design with low-latency emphasis. Trading-flavored: order book, market data feed, position tracker. Latency budgets and ordering guarantees graded."

    Source · everythingquant.com Jane Street guide
  • Behavioral

    "Tell me about a complex technical project you've worked on. Be ready for deep questions on every implementation choice."

    Source · janestreet.com/preparing-for-a-software-engineering-interview, blog.janestreet.com dev interview
  • Behavioral

    "Discuss a math or CS concept you find genuinely interesting. Why? What problems does it apply to?"

    Source · interviewquery.com Jane Street 2025
  • Behavioral

    "Why Jane Street specifically? Generic 'I want to work in finance' fails. Jane Street values intellectual passion — show specific engagement with their work, blog, or open-source contributions."

    Source · janestreet.com official, blog.janestreet.com
Common signals to fix

What gets you rejected at this level

  • Trying OCaml for the first time in the interview

    Jane Street EXPLICITLY discourages this. From their official prep page: 'Please don't use OCaml just because you think it will make us happy.' Most hires don't know OCaml coming in. Use the language you're most comfortable with — not OCaml unless you've used it for months.

  • Solutions without functional-style decomposition

    Jane Street values clear thinking via modular helper functions. Monolithic 'one big function' solutions — even if correct — flag missing functional thinking. Decompose problems even when using Python or other imperative languages.

  • Weak probability / mathematical reasoning

    Jane Street's culture values mathematical depth. Candidates who can't engage with probability brainteasers, conditional probability, or expected value flag missing baseline preparation. Practice probability puzzles specifically before the interview.

  • Generic 'I want finance' answers

    Jane Street values intellectual passion specifically. Generic 'I want to work in finance' or 'I admire Jane Street' answers fail. Reference specific Jane Street blog posts, open-source contributions, or engineering practices that resonate.

  • Weak game-based reasoning

    Jane Street's game-based round tests real-time reasoning under uncertainty. Candidates who freeze when facing a probability game with limited information flag missing intuition. Practice mathematical games (auction theory, simplified market making) before the loop.

How Applr's AI mock interview tracks Jane Street's rubric

Applr's Jane Street mock simulates the game-based round format — real-time mathematical games with reasoning-under-uncertainty graded explicitly. Coding rounds emphasize functional-style decomposition (modular helpers, clear thinking) regardless of language used.

The behavioral round prompts intellectual passion specifically — generic 'I want to work in finance' answers get flagged with rewrites that surface specific Jane Street engagement (blog posts, open-source contributions, engineering practices).

Adjacent loops

Related practice

FAQ

Should I learn OCaml before the interview?

Per Jane Street's official prep page (janestreet.com/preparing-for-a-software-engineering-interview) and Jane Street engineering blog: NO. They explicitly discourage learning OCaml just for the interview. Most hires don't know OCaml coming in. Use the language you're most comfortable with. Practice solving problems in functional style (modular helpers, clear decomposition) — even in Python — to show functional thinking without needing OCaml fluency.

What's the game-based round really like?

Per algo.monster's Jane Street guide and Jane Street's engineering blog 'What a Jane Street dev interview is like': you play a real-time mathematical game with the interviewer. Could be a simplified auction, a probability estimation under limited information, or a market-making simulation. The dimension graded is how you reason under uncertainty in real time — not whether you 'win' the game. Practice mathematical games and probability puzzles before the loop.

How important is competitive math/programming background?

Per the wallstreetquants.com Jane Street salary guide and 2025 candidate reports: Putnam, IMO, USACO, ICPC results are explicitly valued in resumes. Strong math olympiad background gives you a clear edge at the screening stage. Without competitive results, strong technical projects + clear functional thinking can still pass — but the bar on the technical rounds is higher.

What's the salary band at Jane Street?

Per wallstreetquants.com Jane Street salary 2025 and 2025 candidate reports: comparable to Hudson River Trading and Citadel — first-year SWE total comp typically $300-450K. At 5 years, standard performers reach $800K-1.2M. Above FAANG but with high performance filtering. Signing bonuses lower than Citadel; base + bonus structure differs.

Does Jane Street sponsor visas?

Yes for SWE roles in NYC and London offices. Visa coordination varies by office and timing — confirm with recruiter early. Hong Kong office also sponsors local visas.

How does Jane Street compare to Citadel and Two Sigma?

All three are top-tier quant firms with comparable total comp at senior levels. Jane Street: trading firm, mathematical thinking valued, OCaml available, game-based rounds, Super-Day format. Citadel: hedge fund + market maker, commercial impact valued, cross-team review, ~$400K first-year SWE. Two Sigma: more conservative comp ($250K first year), distributed systems + low-latency required, ChatGPT prohibited. Pick by which culture/technical focus resonates.

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