How long does the Duffel interview process take?

Most candidates spend between 4 and 8 weeks from recruiter screen to offer. The onsite loop itself runs in a single day or is split across two half-days, with debrief and offer typically within 5 business days after.

How should I prepare specifically for Duffel?

Focus on three things: (1) the company DNA shown above — what they actually grade for, (2) the rounds in your loop, especially the round most candidates underestimate, and (3) drilling on the question types in this guide using a structured framework like CIRCLES or STAR.

Does this apply to engineering or design roles at Duffel?

The DNA stays the same — what changes is the round mix. SWE candidates face coding screens instead of Product Sense; designers face portfolio reviews and design exercises. The "what they value" and behavioral signals carry across all functions.

Other roles at Duffel:Product Manager Software Engineer Sales Customer Success Solutions Architect

Growth · Software Engineer Interview Guide

Applies via Ashby

How to Pass the Duffel Software Engineer Interview in 2026

The Duffel DNA (TL;DR)

Duffel values candidates who demonstrate strong analytical problem-solving, technical proficiency, and a deep understanding of API-first products. They seek individuals who are proactive, customer-centric (especially for developer users), and thrive in a fast-paced, evolving travel tech landscape.

The Duffel Interview Loop

Your onsite loop will typically consist of 5 rounds.

1
Round 1
Recruiter Screen
Motivation, role fit, logistics.
2
Round 2
Coding Screen
LeetCode-medium algorithmic problems under time pressure.
3
Round 3
System Design
Distributed systems, trade-offs at scale, architecture under constraints.
4
Round 4
Onsite Coding
LeetCode-hard, debugging, code clarity, edge cases.
5
Round 5
Behavioral / Leadership
Past evidence of ownership, influence, resolving conflict.

The Danger Zone: Top Reasons Candidates Fail

Based on our database of Duffel interview outcomes, avoid these common traps:

Not considering circuit breaker patterns or fallback mechanisms.
Failing to articulate specific actions taken beyond just 'raising awareness'.
Focusing only on the negative aspects without highlighting learning or positive outcomes.
Describing a situation where they simply stated their opinion without a strategy for persuasion.

Test Yourself: Real Duffel Questions

Three real prompts pulled from our database.

Type · Algorithmic

Given a list of flight bookings (each with a departure time, arrival time, and origin/destination airport codes), find the earliest possible connection time for a passenger needing to travel between two specified cities, considering layover times.

Type · Role Fit

Describe your experience with building and maintaining APIs, particularly in a context where reliability and performance are critical.

Type · Scalability

How would you design a system to handle a sudden surge in flight searches during a major travel sale event (e.g., Black Friday)? Discuss potential bottlenecks and solutions.

+ many more questions, signals, and worked examples

Unlock the rubric →

Duffel Interview Question Bank

A sample from our database, grouped by round. Sign up to see the full set.

10 of 23 questions shown

Recruiter Screen

1
Type · Motivation
What interests you about working at Duffel, specifically within the travel tech industry and our mission to simplify travel for businesses?
2
Type · Role Fit
Describe your experience with building and maintaining APIs, particularly in a context where reliability and performance are critical.
+ 1 more questions in this round (sign up to unlock)

Coding Screen

3
Type · Algorithmic
Given a list of flight bookings (each with a departure time, arrival time, and origin/destination airport codes), find the earliest possible connection time for a passenger needing to travel between two specified cities, considering layover times.
4
Type · Data Structures
Implement a data structure that can efficiently store and retrieve flight routes between multiple cities, supporting queries for all direct flights from a given city and all flights arriving at a given city.
+ 1 more questions in this round (sign up to unlock)

System Design

5
Type · API Design
Design the API for Duffel's flight search service. Consider how users will specify search criteria (dates, destinations, number of passengers, cabin class) and how results will be returned, including pagination and filtering.
6
Type · Scalability
How would you design a system to handle a sudden surge in flight searches during a major travel sale event (e.g., Black Friday)? Discuss potential bottlenecks and solutions.
+ 1 more questions in this round (sign up to unlock)

Onsite Coding

7
Type · Debugging
Here is a piece of code that calculates flight prices. It occasionally returns incorrect results for complex itineraries. Debug this code, identify the root cause, and provide a corrected version.
8
Type · Code Quality
Refactor the following function, which fetches and processes flight data, to improve its readability, testability, and performance. Ensure it adheres to best practices.
+ 1 more questions in this round (sign up to unlock)

Behavioral / Leadership

9
Type · Conflict Resolution
Tell me about a time you had a significant disagreement with a cross-functional team member (e.g., engineer, designer, marketer) about a product decision. How did you approach it, and what was the outcome?
10
Type · Ownership
Tell me about a time you took ownership of a problem that wasn't strictly within your job description. What was the situation, and what did you do?
+ 9 more questions in this round (sign up to unlock)