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Screna has 7 Retell AI interview write-ups. The most reported round is the system design round (4).

7 interview notes · updated Jul 2026

Retell AI·Software Engineer·Onsite - System Design / Architecture

Jul 2026
System design round at Retellai for a software engineer role, pretty much one big question about building a collaborative doc editor. The whole session was focused on concurrency, which I was not fully prepared for at that depth.
  • Design the backend for a real-time collaborative document editor. Focus on how multiple users can edit the same document simultaneously without losing or duplicating content, and how all clients eventually converge to the same state.

“This was the whole interview basically.”

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Retell AI·Software Engineer·Onsite - System Design / Architecture

Jun 2026
Retell SWE interview that was basically 'build a mini SQL engine from scratch.' Three parts: architecture, core implementation, then keep extending it as the interviewer piles on features. More open-ended than I expected, less about grinding leetcode and more about whether you can scope a real system under pressure.
  • Design and implement a small in-memory SQL query engine that takes a SQL string and executes it against in-memory tables. Start with a basic subset and be ready to extend as features get added.
  • Before writing any code, walk through the architecture of the query engine. What are the components, what does each consume and produce, and where do future features like JOIN or GROUP BY plug in?
  • Implement the core engine: parse and execute SELECT with a WHERE clause supporting comparison operators and AND/OR logic.
  • Extend the engine to support ORDER BY and LIMIT, aggregate functions with GROUP BY, and an INNER JOIN between two tables.
  • How would you support joining three or more tables, and how does join order affect performance?
  • How would you add HAVING and subqueries to your AST and executor?
  • Where would a query optimizer fit in your design, and what is one rewrite that would help performance?
  • How would you test this engine to stay confident it's correct as you keep adding features?

“The scoping part is what tripped me up at first.”

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Retell AI·Frontend Engineer·Technical Phone Screen

May 2026
Short technical screen for a frontend role at RetellAI. Just one question that I remember but it was a good signal about how they think about UI performance.
  • If you're building a search bar, how would you avoid firing a request on every single keystroke?

“Pretty classic frontend question but I second-guessed myself mid-answer.”

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Retell AI·Software Engineer·Onsite - System Design / Architecture

May 2026
RetellAI software engineering interview with a system design question that had a fairness angle I wasn't really prepared for. Decent question, made me think harder than I expected.
  • Design a scheduling system that assigns tasks to workers or workers to shifts. Beyond just making it work, the schedule needs to be 'fair': balanced workload, no one repeatedly stuck with the worst slots, no consecutive overnight shifts, etc. Define what fairness means, propose an algorithm, and walk through the trade-offs compared to a pure greedy approach or a full optimization solver.

“The fairness definition part tripped me up first.”

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Retell AI·Software Engineer·Onsite - System Design / Architecture

Apr 2026
System design round at Retell for a software engineer role. The whole thing was one big open-ended problem about designing a programmatic outbound calling platform, and they expected you to drive the conversation yourself rather than wait for prompts. Scale was clearly the part they cared most about.
  • Design an outbound calling platform end to end: how does an enterprise API request turn into a phone call, how do you track call state, and how does the system hold up under load?
  • A burst of thousands of call requests arrives in seconds from multiple enterprise customers. How do you keep the platform stable, respect carrier concurrency and per-second rate limits, and stay fair across tenants?
  • How do you enforce a per-carrier concurrency budget across a distributed fleet of dialer workers without over-dialing?
  • A carrier starts showing elevated failure rates and high latency. How does the system detect this and reroute traffic without causing a retry storm?
  • How do you handle retries safely so a client retrying a failed API call never results in the same phone number being dialed twice?
  • How would you support scheduled calls and calling-window compliance, for example never dialing a recipient before 9am in their local timezone?
  • What happens on the answered leg of the call, and what new scaling constraints does bridging to a real-time AI voice agent introduce?

“This is the core question and it's basically a full system design in one prompt.”

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Retell AI·Frontend Engineer·Technical Phone Screen

Apr 2026
Interviewed for a frontend role at RetellAI and got asked about React hooks. Pretty standard technical screen, nothing too wild.
  • What are React hooks and when would you use them?

“Classic question but I still fumbled the 'when to use them' part a bit.”

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Retell AI·Frontend Engineer·Technical Phone Screen

Apr 2026
Short technical screen for a frontend role at RetellAI, just one question about the Virtual DOM.
  • Can you explain what the Virtual DOM is?

“Classic React fundamentals question.”

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