Sefism is free for learners. We are here to help you grow, one step at a time.Join for free
Sefism.
Ed techProduct company

Duolingo

Builds a mobile app for learning languages, along with courses in maths, music and chess, and the Duolingo English Test.

Not known6 stage process documentedFounded 2011
Headquarters

Pittsburgh, Pennsylvania, United States

Headcount

250 to 1,000

250 to 999 people
Work model

Not known

Hiring

Not known

Not enough signal to say. Check the careers page directly.
Where to apply
Careers pageWebsite

Ask for a referral to Duolingo

A referral only means something if the person giving it can actually speak to your work. I will refer you where I know someone on the inside and your profile genuinely fits the role, and I will tell you plainly when I cannot. Either way you get an answer, and a straight one.

  • I read every request. A reply takes a few days, sometimes longer.
  • I will not refer someone for a role their profile does not fit. It wastes your time and costs me the contact.
  • Where I cannot refer you, I will say why, and point you at the way in that does work.
  • Nothing you send here is shared with anyone without you agreeing to it first.

If you found the opening, paste it. It tells me which team you mean.

A Drive, Dropbox or personal-site link is fine. Make sure it opens without a request for access, or I cannot read it.

At least a short paragraph. This is what I would be putting my name behind, so specifics beat adjectives.

Comma separated, up to six. Things you would be happy to be tested on.

How they hire

The process has a pre-onsite phase and a virtual onsite that can run over one or more days. Each role gets its own interview plan from the recruiter, so not every candidate sees every stage listed here. The online coding task and whiteboard round apply to university and new graduate roles.

  1. 1

    Online coding task (new graduates only)

    Official
    Online test1 hoursRemote

    An automatically graded algorithm problem done on your own time, judged on correctness and efficiency. Python, Java or JavaScript.

    Algorithms
  2. 2

    Technical video interview

    Official
    Live coding1 hoursRemote

    Live coding with a Duolingo engineer on CodeSignal, looking at how you approach and then carry out a solution.

  3. 3

    Pair programming

    Official
    Technical interview1.3 hoursRemote

    Part of the virtual onsite. You work with an engineer inside a codebase that resembles production, to show you can pick up code written by others.

  4. 4

    Code review

    Official
    Technical interview1 hoursRemote

    You review a change, point out problems and suggest improvements. There are versions tailored to backend, iOS and Android.

    Code quality
  5. 5

    Whiteboard interview (new graduates only)

    Official
    Live coding1 hoursRemote

    Problem solving on a virtual whiteboard in the language of your choice, with the focus on explaining your reasoning.

  6. 6

    Design interview

    Official
    System design1 hoursRemote

    A high-level architecture discussion where the approach matters more than reaching one particular answer.

What comes up

Recurring themes from candidate accounts, not a question bank. Nobody is served by leaked question lists, least of all you in the interview.

  • Working in someone else’s code

    Official

    Pair programming and code review both test how you read, question and improve existing code, not just how you write fresh solutions.

  • Fundamentals and complexity

    Official

    Duolingo advises brushing up on data structures and big-O analysis, starting with a simple solution before optimising, and checking edge cases.

  • Thinking out loud

    Official

    Interviewers want to hear your reasoning, see you ask clarifying questions and watch you use hints when you get stuck.

Worth reading before you apply

From the Sefism resource library, matched to the rounds above.

Course
Grokking Data Structures & Algorithms for Coding Interviews

A foundations course that builds eleven core data structures from the ground up (arrays, matrices, stacks, queues, linked lists, trees and BSTs, hash tables, hash sets, heaps, graphs and tries), then covers sorting, searching, greedy and divide and conquer. Every chapter has practice problems, flashcards and an assessment. It suits students and career switchers whose foundations came from tutorials and who find pattern courses move too fast.

  • Job search
  • DSA
  • CS fundamentals
Design Gurus · Interview Prep · 4 to 6 weeks · Beginner
SubscriptionDetails
Platform
Design Gurus Problem Set

A browsable practice library of coding problems that can be filtered by pattern, data structure, difficulty and company, so you can drill exactly the weakness you found this week. Patterns include two pointers, sliding window, hash maps, stacks, backtracking and greedy algorithms, with company filters for Google, Meta, Microsoft, Amazon, Oracle and LinkedIn. Free to browse, with an in-browser editor and solutions.

  • Job search
  • DSA
Design Gurus · Interview Prep · Ongoing
FreeDetails
Guide
Design Gurus Newsletter

A free newsletter of short, focused posts on system design and problem solving, from the team behind the Grokking courses. Recent posts cover company interview processes (such as OpenAI and Anthropic roles), the most asked mobile system design questions and preparation plans, each linking to a fuller article on the blog. It suits engineers who want a steady, low-effort way to keep system design and interview topics fresh between deeper study sessions.

  • System design
  • DSA
Design Gurus · System Design
FreeDetails
Guide
GeeksforGeeks

A very large site of articles on data structures, algorithms and core CS subjects such as operating systems, DBMS, computer networks and OOP, usually with code in several languages, plus practice problems and paid courses. It is handy for revising a university topic or finding a worked example of a specific algorithm. Quality varies because much is community written, so cross-check anything surprising against a textbook or official documentation.

  • DSA
  • CS fundamentals
  • Databases
GeeksforGeeks · Other · Ongoing reference
FreeDetails
Roadmap
Sefism CS Core Subjects Roadmap

An eight-stage roadmap through the core CS subjects: how a computer runs a program, OOP and design, operating systems, computer networks, database theory and internals, software engineering and theory, finished with a systems project such as a shell, an HTTP server or a tiny database. It suits CS students and self-taught developers filling the same gaps, and favours understanding shown in working code over memorised answers.

  • DSA
  • CS fundamentals
  • Databases
Sefism · Other · About 216 hours, 22 to 46 weeks · Beginner
FreeDetails
Course
Advanced System Design Interview, Volume II

The second volume of Grokking the System Design Interview, aimed at senior and staff (L5/L6) design rounds. It works through harder case studies such as a payment system, flash sale, notification service, unique ID generator, Gmail, Reddit, Google Calendar and a code judging system, then goes beneath them with patterns like quorum, write-ahead logs and vector clocks and deep dives into Dynamo, Cassandra, Kafka, Chubby, HDFS, GFS and BigTable.

  • System design
  • Backend
  • Job search
Design Gurus · System Design · About 36 hours · Advanced
SubscriptionDetails
Browse the whole library

What it pays

Nothing collected for this company yet, and nothing worth guessing at. A made-up range is worse than no range because people negotiate against it.

Add to the Duolingo page

This library is only as good as what people who have been through it are willing to share. Most of these companies have no hiring process documented anywhere, and one account of what the rounds actually were is worth more than anything I can research from the outside.

What are you adding?

This decides how the claim is labelled on the page. Only someone representing the company can produce an “official” label, and I check that separately.

Year and month.

Comma separated topics, not the questions themselves.

Round by round is ideal: what each one was, how long, remote or in person, and what it covered.

Credit

Anonymous is the default. If you keep it anonymous, nothing identifying you reaches the page: it is published as a candidate account and your name stays with me. Never send anything covered by an NDA, and never send a take-home or a question paper.

Universities they recruit from

No sourced university links yet. A campus drive, a career fair appearance or an internship partnership is what puts a university here.

Add to the Duolingo page

This library is only as good as what people who have been through it are willing to share. Most of these companies have no hiring process documented anywhere, and one account of what the rounds actually were is worth more than anything I can research from the outside.

What are you adding?

This decides how the claim is labelled on the page. Only someone representing the company can produce an “official” label, and I check that separately.

Year and month.

Comma separated topics, not the questions themselves.

Round by round is ideal: what each one was, how long, remote or in person, and what it covered.

Credit

Anonymous is the default. If you keep it anonymous, nothing identifying you reaches the page: it is published as a candidate account and your name stays with me. Never send anything covered by an NDA, and never send a take-home or a question paper.

How to actually get seen

Practise reviewing pull requests and finding your way around an unfamiliar codebase, since two onsite rounds are built around that. Ask your recruiter for the exact plan for your role early.

Sources

Whole profile last checked 2026-09-22.

Interviewed at Duolingo? Fill in what changed.

Processes change, rounds get added, tests get replaced. If what you went through was different from what is on this page, tell me and I will update it.

Want me to refer you here?

Send me the role, your CV and a few honest paragraphs on why you fit it. Where I know someone inside and your profile matches, I will make the introduction. Where I cannot, I will tell you why and point you at the route that does work. You get an answer either way.

Ask for a referral to Duolingo

A referral only means something if the person giving it can actually speak to your work. I will refer you where I know someone on the inside and your profile genuinely fits the role, and I will tell you plainly when I cannot. Either way you get an answer, and a straight one.

  • I read every request. A reply takes a few days, sometimes longer.
  • I will not refer someone for a role their profile does not fit. It wastes your time and costs me the contact.
  • Where I cannot refer you, I will say why, and point you at the way in that does work.
  • Nothing you send here is shared with anyone without you agreeing to it first.

If you found the opening, paste it. It tells me which team you mean.

A Drive, Dropbox or personal-site link is fine. Make sure it opens without a request for access, or I cannot read it.

At least a short paragraph. This is what I would be putting my name behind, so specifics beat adjectives.

Comma separated, up to six. Things you would be happy to be tested on.

Add to the Duolingo page

This library is only as good as what people who have been through it are willing to share. Most of these companies have no hiring process documented anywhere, and one account of what the rounds actually were is worth more than anything I can research from the outside.

What are you adding?

This decides how the claim is labelled on the page. Only someone representing the company can produce an “official” label, and I check that separately.

Year and month.

Comma separated topics, not the questions themselves.

Round by round is ideal: what each one was, how long, remote or in person, and what it covered.

Credit

Anonymous is the default. If you keep it anonymous, nothing identifying you reaches the page: it is published as a candidate account and your name stays with me. Never send anything covered by an NDA, and never send a take-home or a question paper.

Work with me

Stuck on something specific?

Writing only gets you so far. If you want an answer to your situation rather than the general case, book a session and we will work through it together. Sessions are free for approved Sefism members, and a few slots open each week.

Book a free sessionSee all services

Follow along

New writing, resources and project ideas land here first.