Retool

Mid-sized

Retool is a low-code development platform that enables companies to quickly build internal tools and business applications by connecting to databases, APIs, and other data sources. It is known for accelerating the creation of custom dashboards, admin panels, and operational software for engineering and business teams.

6 interview notes · updated Jul 2026

Retool·Software Engineer·Technical Phone Screen

Jul 2026

Retool SWE interview with a coding problem that looks like a standard stock trading question until you read it more carefully. The forced-trade constraint is what makes it interesting, since you can't just skip bad days.

Given an array of daily stock prices, implement two functions: one that finds the maximum profit from exactly one buy-sell transaction (including the least-loss scenario if prices only fall), and another that does the same for exactly two non-overlapping transactions. You must always perform the required number of trades, even if that means taking a loss.

“The 'exactly one transaction' part I got pretty fast.”

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Retool·Software Engineer·Onsite - System Design / Architecture

Jul 2026

System design round at Retool for a software engineer role. The whole thing was one big design question about a car rental platform, which sounds manageable until you realize how many moving parts they actually want you to cover.

Design a car rental platform. Walk through the core entities, the relational schema, and the API layer.
How would you handle availability search by location and date range without double-booking?
Describe the pick-up and return workflows, including how you handle mileage, fuel, damage, and late fees at return.
Walk through your pricing model: base rates, mileage overages, insurance add-ons, promotions, and taxes.
Design 3 to 5 REST endpoints for this platform. What are the request and response shapes?
How would you scale this system as load grows? Think about read replicas, partitioning, and caching.

“This question is deceptively wide.”

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Retool·Software Engineer·Technical Phone Screen

Jun 2026

Retool SWE interview focused entirely on building a Markov chain simulator from scratch. Two-part coding problem that escalated from counting transitions to weighted random sampling, plus a discussion on edge cases and extensions. Pretty algorithmic for a company known for product tooling, which surprised me a bit.

Given a sequence of tokens, build a function that returns, for each token, a mapping of every token that follows it to how many times that transition occurs in the sequence.
Convert those transition counts into probabilities and implement a sample_next(T) function that returns a next token sampled according to those probabilities.
How would you handle tokens that never appear as a predecessor, numerical precision issues in very long sequences, and extending the model to higher-order k-gram chains?

“Pretty clean once you just think of it as iterating pairwise through the list.”

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Retool·Software Engineer·Technical Phone Screen

Jun 2026

Retool software engineer interview that was basically a two-part stock trading problem. The twist was the 'exactly' constraint instead of the usual 'at most', which sounds minor but genuinely changes how you think about the DP states.

Given an array of daily stock prices, complete exactly one buy followed by one sell (sell day must be strictly after buy day). Return the maximum profit, or indicate that no valid transaction exists.
Extend the problem to exactly two non-overlapping buy-sell transactions. Both transactions are required, not optional. Return the maximum combined profit across both.

“The linear scan approach came to me pretty fast, track the running minimum and compute profit at each step.”

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Retool·Software Engineer·Technical Phone Screen

Jun 2026

Retool had me build a mini SQL engine in Python during a technical screen, which sounds manageable until they start layering on GROUP BY and HAVING and asking you to justify your operator ordering out loud.

Implement a SQL execution engine over an in-memory table in Python. The table is a list of dicts. Support SELECT with column projection, WHERE with comparison operators, and LIMIT.
Extend the engine to support GROUP BY with aggregate functions (COUNT, SUM, AVG, MIN, MAX), then add HAVING to filter on aggregated results.
How would you design the API so these operators compose cleanly, for example using an iterator or operator-tree style? What are the time and space complexity tradeoffs?

“I started with WHERE filtering since that felt most natural, then bolted on SELECT projection and LIMIT after.”

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Retool·Software Engineer·Onsite - System Design / Architecture

May 2026

System design round at Retool for a software engineer role. The whole session was centered on designing a dog-walking marketplace backend, which sounds cute until you realize how many moving parts they actually want you to cover.

Design the backend for a two-sided dog-walking marketplace where owners can search for nearby walkers and book them, and walkers can manage their availability and get paid after each walk.
How would you handle geo-based walker search at scale? Walk through your indexing approach.
How do you prevent a walker from being double-booked for the same time slot?
How would you design the payments flow, specifically around capturing payment on walk completion and ensuring idempotent payouts to walkers?
How would you scale the walker discovery layer to handle a large number of read requests?

“This is a big one.”

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