Jane Street

What the sources establish

Jane Street’s current software engineering preparation page (undated) says every SWE path includes a technical interview over Zoom and in-person final rounds at an office that focus mostly or entirely on collaborating on coding problems. Candidates write real code in any language (OCaml earns no bonus), problems are open-ended rather than trivia or “aha” puzzles, and SWE interviews explicitly exclude mental math, math-olympiad and logic-puzzle questions, which belong to other Jane Street roles. Its official mock-interview video (2023) walks through a typical interview on a retired question and ends with advice on communication, clear and correct code, and practice. A 2017 Jane Street blog walkthrough of a retired phone question shows how one problem is extended in stages. Not established: the number and length of final-round interviews and any explicit AI or tool policy.

1. Jane Street: Preparing for a Software Engineering interview

   Official

   Jane Street. Undated page; read 2026-10-05. Read in full for this page.

   Scope: Software engineering candidates on all paths (experienced, students and new grads); explicitly distinct from roles that use mental math or logic puzzles.

   Documented by this source

   • All SWE paths include a technical interview over Zoom and continue to in-person final rounds at an office that focus mostly, if not exclusively, on collaborating on a series of coding problems.
   • Write real code, not pseudocode, in any language; the one you know best is recommended, switching while exploring is fine, and you should know basic data structures and APIs in it.
   • No mental math, math-olympiad or logic-puzzle questions for software engineers; those belong to other Jane Street roles.
   • Open-ended problems with several angles of attack are preferred over algorithm trivia and “aha” puzzles, and the path through the interview matters more than the final solution.
   • Concrete suggestions: be nice, be clear, know your language, and know what you don’t know.
   • No extra credit for OCaml or functional programming, and advanced degrees are not required.
   • Every application is reviewed by a person and answered, ideally within about a week.
   • Recommended preparation is practice, using Jane Street’s written walkthrough of a former question and its mock interview video.

   Outside or AI tools, according to this source: No rule about AI or outside tools is stated; only language choice is covered. Follow the instructions in your own assessment invitation.

   • Undated; it does not give the number or length of final-round interviews.
   Open source(opens in a new tab)Link responded, 5 Oct 2026

2. Jane Street: Software Engineering Mock Interview

   Official

   Jane Street. Undated page; the embedded video’s metadata indicates 2023; read 2026-10-05. Only partly readable when checked.

   Scope: Software engineering interviews; a recorded mock session between two Jane Street engineers.

   Documented by this source

   • A recorded walk-through of a typical SWE interview using a now-retired question, so it shows the format and expectations rather than material to memorize.
   • Per the chapter list, the interviewer first explains the shape of the interview and introduces the question; the candidate discusses ideas from about 5:17, starts coding at about 10:32, and the mock interview ends at 33:45.
   • Closing advice from the two engineers covers communication, clear and correct code, and practice.
   • Practice advice: start a timer, talk through ideas out loud, and write out every part of the problem, including the parts that seem easy.
   • LeetCode and HackerRank are suggested as sources of algorithmic practice, with the note that their questions differ from what you will get in a Jane Street interview.

   Outside or AI tools, according to this source: Not addressed. Follow the instructions in your own assessment invitation.

   • We read the page text and chapter list; the video has no transcript and was not reviewed, so its question is not described here.
   • A mock session: real interviews differ in question and pacing.
   Open source(opens in a new tab)Link responded, 5 Oct 2026

3. What a Jane Street software engineering interview is like (Jane Street Tech Blog)

   Official, historical

   Jane Street Tech Blog. Published 2017-02-28; read 2026-10-05. Read in full for this page.

   Scope: The SWE phone interview as of 2017, illustrated with a retired question; linked from the current SWE preparation page as its written walkthrough.

   Documented by this source

   • The phone interview used a shared online editor, with real code in any language and no preference for OCaml.
   • Retired question “Memo” in three parts: write a memoizing wrapper (typically with a hash table), bound its memory with O(1) FIFO eviction, then discuss LRU eviction (possibly implementing parts), which can reach O(1) with a hash table plus a doubly linked list.
   • The 2017 bar: a bug-free first part quickly; most passing candidates complete part two; strong candidates finish part three, though not finishing it is not automatically a rejection.
   • Candidates who recognize a question should say so, and candidates are asked not to share questions.
   • In 2017, onsite interviews ran much like the phone interview, with all questions technical.

   Outside or AI tools, according to this source: Not addressed beyond the shared editor and language choice. Follow the instructions in your own assessment invitation.

   • Dated 2017; the current page says the first interview is over Zoom and final rounds are in person, so follow the current page for logistics.
   • The question is retired: use it to see how a problem is extended, not as likely content.
   Open source(opens in a new tab)Link responded, 5 Oct 2026

Our preparation recommendation

Our preparation suggestion, not a Jane Street statement. The SWE page rules out mental math and logic puzzles for software engineers, so trader-style drills are not part of SWE preparation. Prepare instead for collaborative, open-ended coding in your strongest real language: fluent use of core data structures and APIs, clear and correct code, talking about complexity and trade-offs as a problem is extended, and being explicit about what you do not know. The retired “Memo” walkthrough grows from basic coding into data-structure design (a hash table plus a queue or linked list), which is why stateful design and complexity get extra weight.

1. Coding fluency and standard-library costsNot started

   “Know your language” is explicit advice, and you must write real code using basic data structures and APIs fluently.

2. Arrays, strings and hashingNot started

   Hash tables anchor the first part of the official walkthrough’s retired question.

3. Linked listsNot started

   The walkthrough reaches O(1) LRU eviction by pairing a hash table with a doubly linked list.

4. Pattern recognition and mixed practiceNot started

   Problems are extended in stages, which rewards stateful data-structure design; this topic covers that pattern.

5. Complexity analysisNot started

   Each extension in the walkthrough asks for tighter time bounds or bounded memory.

6. Correctness, invariants, edge cases and testingNot started

   The mock interview’s advice stresses clear and correct code, and the walkthrough expects a bug-free first part.

7. Explaining solutions aloudNot started

   “Be clear” and “know what you don’t know” are among Jane Street’s explicit suggestions.

8. Mock interviews and timed practiceNot started

   Jane Street’s own practice advice: use a timer, talk aloud and write out every part of a solution.

Confirm with your recruiter

• Which interviews your path includes (the page describes a Zoom technical interview, then in-person final rounds) and how many final-round interviews to expect.
• Your path and level (experienced, student or new grad) and any differences in the process.
• That the coding environment supports the language you plan to use, and whether you can run code.
• Tool and AI rules for the Zoom interview and the final rounds; the SWE page states none.
• Whether any online assessment or take-home applies to your path (none is mentioned for SWE).
• Logistics for the in-person final round: office, travel and schedule.
• Which role you are interviewing for if you are also considering trading or research, since those roles use different preparation (mental math, puzzles) that does not apply to SWE.

Limitations of this page

• Jane Street’s pages give no round counts or durations for real interviews.
• The mock video was not watched; it is described from its page and chapter list.
• The Memo walkthrough is from 2017 and uses a retired question.