Headway Interview Questions — Page 1

Headway·Software Engineer·Onsite - System Design / Architecture

Apr 2026

System design round at Headway for a software engineering role. The whole thing was basically one big capacity estimation problem, which I wasn't fully prepared for in terms of how rigorous they wanted the math to be.

Given a number of users and how active each one is, estimate the server capacity needed: CPU, memory, disk IOPS, and network bandwidth. Walk through the full calculation from scratch.

“I started with DAU and per-user request rate to get QPS, which felt fine, but then they wanted me to explicitly cost out CPU and memory per request and I fumbled around for a bit.”

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Headway·Software Engineer·Onsite - System Design / Architecture

Apr 2026

System design round at Headway for a software engineer role, focused entirely on building out the search experience for a short-term rental platform. It was a deep one, covering data modeling, API design, indexing strategy, ranking, and scale all in one go.

Design the search experience for a short-term rental platform like Airbnb, covering functional requirements, data model, API design, indexing strategy, ranking, and scalability.

“This was a lot to cover in one session.”

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Headway·Software Engineer·Onsite - System Design / Architecture

Apr 2026

System design interview at Headway for a software engineer role. Two questions, both focused on backend scaling under load. Pretty technical throughout, no behavioral stuff at all.

Your backend service is timing out under high request volume. How do you diagnose what's wrong and what do you do about it, both right now and longer term?
Given a set of assumptions about users, request rates, and data volume, how would you estimate the server capacity you actually need?

“I started with the obvious stuff, check metrics, look at CPU and memory, see if it's the DB choking or the app layer.”

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Headway·Software Engineer·Technical Phone Screen

May 2026

Headway software engineer interview with a debugging scenario built around a log parsing class. Three connected parts, all feeding into each other, which was a bit stressful once I realized fixing part one was the key to everything downstream.

You're given a LogEntry class where the constructor stores a timestamp token as a string. The downstream speed calculation is broken because of this. Find the bug, fix it, and write a small test to confirm the time-delta math works.

“I actually spotted the type issue pretty fast, tokens[0] staying as a string means any arithmetic on timestamps just blows up.”

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Headway·Software Engineer·Technical Phone Screen

May 2026

Coding round at Headway for a software engineer role. The problem was built around an obstacle course race tracker, and you had to debug a broken implementation, then add two new methods, then talk through testing and code quality. Pretty involved for a single session.

There's a bug in this RunCollection implementation that's causing a test to fail. Find and fix it.
Implement a best_of_bests() method that computes the theoretically fastest possible run time by taking the minimum recorded time for each obstacle index across all runs, including incomplete ones.
Implement chance_of_personal_best(test_run) using a Monte Carlo simulation over 10,000 trials, sampling remaining obstacle times from historical data and returning the fraction of trials that beat the current personal best.
What additional tests would you write beyond the ones already provided, and what improvements would you make to the codebase after implementing these methods?

“Debugging someone else's code under time pressure is its own skill and I don't think I'm great at it.”

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Headway·Software Engineer·Technical Phone Screen

Jun 2026

Coding round at Headway for a software engineer role. The problem looked like a straightforward parsing task but the speeding logic had a second condition that tripped me up a bit.

You're given camera log entries from a segmented road system. Each entry records a vehicle plate and a timestamp when it crosses a segment boundary. Implement a function that returns all plates of vehicles caught speeding, where speeding means either a single segment averaged 130 km/h or more, or at least two separate segments each averaged 120 km/h or more.

“The parsing part was fine, I sorted by timestamp per plate and computed speed as 36000 divided by the time delta.”

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Headway·Software Engineer·Onsite - System Design / Architecture

Jun 2026

System design round at Headway for a software engineer role. The question was a classic 'slow server under load' scenario but they wanted you to go pretty deep across a lot of dimensions, not just say 'add more servers' and call it a day.

Your server is getting slow because of a sudden spike in incoming requests. How do you diagnose and fix it?

“I started with horizontal scaling and load balancers which was fine, but I jumped there too fast without talking about profiling first.”

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Headway·Software Engineer·Onsite - System Design / Architecture

Jun 2026

Twenty-minute system design discussion at Headway for a software engineer role. Nothing algorithmic, just a back-and-forth about building a comment service. Felt more like a whiteboard conversation than a formal interview, which I wasn't quite expecting.

Design a service that allows users to add and retrieve comments on articles, supporting pagination and optional features like threaded replies and edit/delete.
How would you handle caching for a read-heavy comment feed, and how do you think about cache invalidation when new comments are added?
How would you partition the comments table to handle high-traffic articles, and what problems does that create?
Should the comment count per article be stored as a denormalized counter or computed on the fly? What are the tradeoffs?
How would you approach rate limiting and spam or abuse prevention for user-submitted comments?
After a user submits a comment, should they immediately see it in the feed? How do you reason about consistency guarantees here?

“I started with the API shape, add_comment and list_comments, which felt natural.”

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Headway·Software Engineer·Technical Phone Screen

Jun 2026

Coding round at Headway for a software engineering role. The problem looked like a stats/probability question dressed up as a racing leaderboard, which threw me off at first. Mostly about finding bugs in starter code and writing tests, not greenfield design.

Given a list of racers each with a list of completion times, implement a function that returns the smallest personal-best time across all racers, where each racer's personal best is their minimum time.
Implement a function that estimates the probability that a given candidate time would be a new personal best for a racer, based on their history. The model assumes times are drawn from a normal distribution fit to the history, and returns the probability that a fresh draw falls below the current minimum.
Identify the bugs in the provided starter code for both functions, fix them, and add unit tests covering the corrected behavior.

“Pretty mechanical once you see it.”

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Headway·Software Engineer·Onsite - Multi Round

Jun 2026

Headway software engineer interview that mixed technical depth with leadership and behavioral themes. Felt like a loop designed to see if you can actually own things end to end, not just write code.

Walk me through one of the most technically challenging projects you've worked on, including your design choices, the trade-offs you made, and what you'd do differently.
Tell me about a significant conflict you had with a peer, cross-functional partner, or manager. How did you understand their perspective, and what did you do to resolve it?
Describe a time you demonstrated technical leadership, whether that was driving a key decision, mentoring someone, improving quality standards, or pushing the team through a hard change.

“This is where i spent most of my prep time and still felt underprepared.”

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