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Growth · Software Engineer Interview Guide

Interview language: English

How to Pass the Greenly Software Engineer Interview in 2026

The Greenly DNA (TL;DR)

Greenly's core mission to simplify carbon accounting for clients like Forvia emphasizes a candidate's ability to translate complex environmental data into actionable insights. They seek individuals who can clearly articulate how their contributions directly advance the company's sustainability goals, as showcased in 'Voir nos cas clients'.

The Greenly 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 Greenly interview outcomes, avoid these common traps:

Choosing a single database technology without considering the different access patterns (e.g., time-series storage vs. relational metadata).
Describing a problem that was minor or easily solved by others.
Focusing only on the technical aspects of software engineering without connecting them to Greenly's mission.
Not validating input data, leading to errors with missing or malformed initiative data.

Test Yourself: Real Greenly Questions

Three real prompts pulled from our database.

Type · Motivation

Greenly aims to decarbonize the economy by helping businesses track and reduce their carbon footprint. What interests you about this mission, and how do you see your software engineering skills contributing to our success?

Type · Coding

Greenly's dashboard displays energy consumption trends. Implement a function that takes a list of historical energy data points (timestamp, consumption) and returns a simplified representation of the trend, such as a list of key points defining the overall shape (e.g., using a line simplification algorithm like Ramer-Douglas-Peucker).

Type · Algorithmic

Given a list of energy consumption readings for various devices over time, write a function to identify and report any devices that show an unusual spike in energy usage compared to their historical average within a given time window. Consider edge cases like new devices or devices with intermittent usage.

+ many more questions, signals, and worked examples

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Greenly Interview Question Bank

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

9 of 16 questions shown

Recruiter Screen

1
Type · Motivation
Greenly aims to decarbonize the economy by helping businesses track and reduce their carbon footprint. What interests you about this mission, and how do you see your software engineering skills contributing to our success?

Coding Screen

2
Type · Algorithmic
Given a list of energy consumption readings for various devices over time, write a function to identify and report any devices that show an unusual spike in energy usage compared to their historical average within a given time window. Consider edge cases like new devices or devices with intermittent usage.
3
Type · Algorithmic
Greenly's platform aggregates data from many sources. Design a data structure and algorithm to efficiently store and retrieve the total energy consumption for a specific building on any given day, considering that data might be updated frequently and queries can span large date ranges.
+ 1 more questions in this round (sign up to unlock)

System Design

4
Type · System Design
Design a scalable system for Greenly that ingests real-time energy meter data from millions of IoT devices across different geographical locations. The system should be able to process this data, store it efficiently, and make it available for analysis and reporting with low latency.
5
Type · System Design
Greenly wants to provide personalized recommendations to businesses on how to reduce their energy consumption and carbon footprint. Design a recommendation engine that can process historical energy data, identify potential savings, and generate actionable insights for different types of businesses (e.g., manufacturing, office buildings, retail).
+ 1 more questions in this round (sign up to unlock)

Onsite Coding

6
Type · Coding
Implement a function that calculates the 'carbon intensity' of electricity for a given region and time, based on a provided dataset of energy sources (e.g., solar, wind, natural gas) and their respective carbon emissions per unit of energy. The function should handle missing data points and potential inaccuracies in the source data.
7
Type · Debugging
A colleague has submitted code that is supposed to calculate the cumulative carbon emissions saved by a user's actions over time. However, it's producing incorrect results for certain scenarios. Debug the provided code snippet and explain your findings and the fix.
+ 1 more questions in this round (sign up to unlock)

Behavioral / Leadership

8
Type · conflict resolution
Tell me about a time you had a significant disagreement with a colleague or team member. How did you handle it, and what was the outcome?
9
Type · Ownership
Tell me about a time you encountered a significant technical challenge or bug in a project that was critical to the business. How did you take ownership of the problem, what steps did you take to resolve it, and what was the outcome?
+ 4 more questions in this round (sign up to unlock)

Unlock all 16 Greenly questions, free

No credit card. Every question with its framework, the grading signals interviewers score against, and a worked answer for each.

Unlock all 16 Greenly questions

Interview tracks at Greenly

How Greenly's DNA translates across functions. Pick your role.

Compare Greenly with similar employers

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Practice Greenly interviews end-to-end

Greenly Mock Interview

Run a live mock interview with our AI interviewer using Greenly-style prompts. Get scored on structure, signal, and answer length - exactly how the real loop grades you.

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STAR Stories for Greenly Behavioral Rounds

Build a Story Bank of your past wins, mapped to the leadership signals Greenly interviewers grade on. Reuse them across every behavioral round.

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Greenly Interview Prep Hub

The frameworks behind every Greenly round: CIRCLES for product sense, hypothesis-driven debugging for analytical, STAR for behavioral. Learn each one in 10 minutes.

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Interview Frameworks

CIRCLES, STAR, AARRR, RICE, MECE. The exact frameworks that make Greenly interviewers nod instead of frown. Step-by-step playbooks with the moves and the pitfalls.

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Sample answers

What a strong answer to these Greenly interview questions shows.

A strong answer shows: Passion for environmental issues; Understanding of Greenly's business model; Ability to connect technical skills to business impact.

A strong answer shows: Correct implementation of a line simplification algorithm; Handling of time-series aspects of the data; Output format is practical for visualization.

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