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Senior Backend Engineer Interview Questions

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2,034 senior backend engineer interview questions shared by candidates

They'll create a private repo with a task (just a README, a few dockerfiles, docker-compose.yml, and some .php files inside), share it with you and expect you'd implement it (in PHP, Python, or Go) in no more than 7 days and then open a single Pull Request on Github with all the changes to submit the result. The task is: 1. Implement Recipes API with the specified endpoints (6 in total) for List, Create, Get, Update, Delete, Rate. 1.1 Implement authentication for the Create, Update, and Delete (according to the task, the method is up to you, but at the end you'll learn that not really). 1.2 Implement search functionality. 1.3 Optional requirements (at the end they may be not that optional): implement pagination, content negotiation, add other types of testing (though, nobody cares), have good git history (even though, nobody would read it). 2. Do not use any frameworks or microframeworks. Code generation of any kind is forbidden. 3. Use Postgres, MongoDB, or Redis for data persistence. 4. Overengineer your solution so they can see what you can do (that's just a beautiful lie they copy pasted from somewhere). 5. Make sure your project works with the specified docker-compose or they will ignore your result right away.
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Senior Backend Engineer

Interviewed at HelloFresh

3.3★
Feb 26, 2018

They'll create a private repo with a task (just a README, a few dockerfiles, docker-compose.yml, and some .php files inside), share it with you and expect you'd implement it (in PHP, Python, or Go) in no more than 7 days and then open a single Pull Request on Github with all the changes to submit the result. The task is: 1. Implement Recipes API with the specified endpoints (6 in total) for List, Create, Get, Update, Delete, Rate. 1.1 Implement authentication for the Create, Update, and Delete (according to the task, the method is up to you, but at the end you'll learn that not really). 1.2 Implement search functionality. 1.3 Optional requirements (at the end they may be not that optional): implement pagination, content negotiation, add other types of testing (though, nobody cares), have good git history (even though, nobody would read it). 2. Do not use any frameworks or microframeworks. Code generation of any kind is forbidden. 3. Use Postgres, MongoDB, or Redis for data persistence. 4. Overengineer your solution so they can see what you can do (that's just a beautiful lie they copy pasted from somewhere). 5. Make sure your project works with the specified docker-compose or they will ignore your result right away.

Design a system that tracks files stored in S3. Given two API endpoints—one that lists the files and another that provides details such as file size—design a system that counts the total number of files and calculates their combined size.
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Senior Backend Engineer

Interviewed at Cyera

4.5★
Mar 8, 2025

Design a system that tracks files stored in S3. Given two API endpoints—one that lists the files and another that provides details such as file size—design a system that counts the total number of files and calculates their combined size.

Different ways to implement and manage threads in Java? Pros and cons of each approach. Why a thread pool size shouldn't be too large or too small? Different way of distributing/batching work across threads. Scaling with queues and databases. How would you implement a distributed rate limiter? (Hint: learn the rate-limiting algorithms). Pros and cons for every question asked.
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Senior Backend Engineer

Interviewed at Monzo Bank

3.9★
Feb 12, 2026

Different ways to implement and manage threads in Java? Pros and cons of each approach. Why a thread pool size shouldn't be too large or too small? Different way of distributing/batching work across threads. Scaling with queues and databases. How would you implement a distributed rate limiter? (Hint: learn the rate-limiting algorithms). Pros and cons for every question asked.

Check if string contains the exact same number of repetitions of every character. I.e. "aabb" - true, "aabbc" - false. Then check if removing a single character from the string can make it valid, i.e. "aabbc" - true, "aaabbbcc" - false
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Senior Backend Engineer

Interviewed at Bolt

3.4★
Dec 13, 2019

Check if string contains the exact same number of repetitions of every character. I.e. "aabb" - true, "aabbc" - false. Then check if removing a single character from the string can make it valid, i.e. "aabbc" - true, "aaabbbcc" - false

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