Type · debugging
A service is failing intermittently during peak hours. The logs show a memory leak in a component that processes high-frequency network telemetry. How do you isolate the root cause?
How to Pass the Iliad / Free Software Engineer Interview in 2026
Enterprise · Software Engineer Interview Guide
Sign up to see ATSHeadquartered in FranceInterview language: French
The Iliad / Free DNA (TL;DR)
Xavier Niel’s disruptive culture prioritizes resourceful, hands-on builders who challenge legacy telecom complexity. Candidates score points by demonstrating cost-efficient architecture decisions for Freebox infrastructure and defending pragmatic execution over theoretical perfection.
The Iliad / Free Interview Loop
Your onsite loop will typically consist of 5 rounds.
- 1
Round 1
Recruiter ScreenMotivation, role fit, logistics. - 2
Round 2
Coding ScreenLeetCode-medium algorithmic problems under time pressure. - 3
Round 3
System DesignDistributed systems, trade-offs at scale, architecture under constraints. - 4
Round 4
Onsite CodingLeetCode-hard problems, reasoning about defects, code clarity, edge cases. - 5
Round 5
Behavioral / LeadershipPast evidence of ownership, influence, resolving conflict.
The Danger Zone: Top Reasons Candidates Fail
Based on our database of Iliad / Free interview outcomes, avoid these common traps:
- Assuming all routers can connect to the server at once
- Failing to define a strategy for handling reconciliation discrepancies
- Suggesting a single database for all write operations
- Failing to account for failover scenarios when a data center goes down
Test Yourself: Real Iliad / Free Questions
Three real prompts pulled from our database.
Type · ownership
Tell me about a time you identified a latent performance bottleneck in a production system that wasn't currently causing an outage but would have during a peak traffic event.
Type · architecture
Design a system to track real-time data usage for millions of mobile subscribers to trigger alerts when they hit their plan limits.
+ many more questions, signals, and worked examples
Sign up to unlock the full Iliad / Free grading rubric
Iliad / Free Interview Question Bank
A sample from our database, grouped by round. Sign up to see the full set.
5 of 10 questions shown
1
System Design
5- 1
Type · architecture
Design a system to track real-time data usage for millions of mobile subscribers to trigger alerts when they hit their plan limits. - 2
Type · architecture
How would you design a fault-tolerant service to distribute firmware updates to millions of home internet routers simultaneously? - + 3 more questions in this round (sign up to unlock)
2
Onsite Coding
1- 3
Type · debugging
A service is failing intermittently during peak hours. The logs show a memory leak in a component that processes high-frequency network telemetry. How do you isolate the root cause?
3
Behavioral / Leadership
4- 4
Type · conflict
Describe a time you had to push back on a feature request from the product team because it would have compromised the stability of the core network service. - 5
Type · ownership
Tell me about a time you identified a latent performance bottleneck in a production system that wasn't currently causing an outage but would have during a peak traffic event. - + 2 more questions in this round (sign up to unlock)
Unlock all 10 Iliad / Free questions, free
No credit card. Every question with its framework, the grading signals interviewers score against, and a worked answer for each.
Interview tracks at Iliad / Free
How Iliad / Free's DNA translates across functions. Pick your role.
Compare Iliad / Free with similar employers
Same DNA, different bar. Browse the closest companies in our database and see how their loops differ.
KPN
Same tierDutch fiber operations at KPN require engineers to show legacy network migration experience while optimizing digital ...
See KPN interview questions
BT Group
Same tierBT Group's 'Group Life' philosophy underpins evaluations, seeking individuals who align with their commitment to Well...
See BT Group interview questions
Vodafone
Same tierThe 'Spirit of Vodafone' principles, particularly 'Keep It Simple,' anchor the loop, where interviewers grade your ab...
See Vodafone interview questions
Practice Iliad / Free interviews end-to-end
Iliad / Free Mock Interview
Run a live mock interview with our AI interviewer using Iliad / Free-style prompts. Get scored on structure, signal, and answer length - exactly how the real loop grades you.
Open
STAR Stories for Iliad / Free Behavioral Rounds
Build a Story Bank of your past wins, mapped to the leadership signals Iliad / Free interviewers grade on. Reuse them across every behavioral round.
Open
Iliad / Free Interview Prep Hub
The frameworks behind every Iliad / Free round: CIRCLES for product sense, hypothesis-driven debugging for analytical, STAR for behavioral. Learn each one in 10 minutes.
Open
Interview Frameworks
CIRCLES, STAR, AARRR, RICE, MECE. The exact frameworks that make Iliad / Free interviewers nod instead of frown. Step-by-step playbooks with the moves and the pitfalls.
Open
Sample answers
What a strong answer to these Iliad / Free interview questions shows.
A service is failing intermittently during peak hours. The logs show a memory leak in a component that processes high-frequency network telemetry. How do you isolate the root cause?
A strong answer shows: Systematic debugging methodology; Understanding of resource management in high-concurrency environments.
Tell me about a time you identified a latent performance bottleneck in a production system that wasn't currently causing an outage but would have during a peak traffic event.
A strong answer shows: Proactive system maintenance; Ability to prioritize technical debt.
Frequently asked questions
How long does the Iliad / Free 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 Iliad / Free?
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 Iliad / Free?
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.
Explore careers on Workfive →