Plaid Software Engineer interview questions

14 Software Engineers have shared notes from their Plaid interviews, with the questions they were asked in each round. That is 67% of the 21 Plaid interview notes on Screna AI.

14 Software Engineer interview notes

Plaid·Software Engineer·Onsite - System Design / Architecture

Jul 2026
System design round at Plaid for a software engineering role, focused entirely on building an in-memory coupon service from scratch. Pretty intense for a single question but they kept piling on follow-ups until the time ran out.
  • Design an in-memory coupon service with addCoupon, redeem, and getRemaining operations. Walk through your data structure choices, explain how you'd achieve O(1) average-case performance, and analyze time and space complexity.
  • How would you handle edge cases like expired coupons, duplicate coupon codes, zero or negative discount values, and exceeding per-user or global redemption limits?
  • How would you make the redeem operation idempotent so retrying a failed request doesn't double-apply a coupon?
  • What edge cases around time would you worry about near a coupon's expiration, such as clock skew or daylight saving transitions?
  • How would you extend the service to support category-based restrictions on coupons, minimum spend thresholds, and bulk coupon input parsing?

“I went straight to hash maps and felt pretty good about it.”

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Plaid·Software Engineer·Onsite - Behavioral / Leadership

Jul 2026
Plaid software engineer interview with a presentation-heavy round that basically turns into a 15-minute interrogation of a project you pick. More prep-intensive than I expected, especially the follow-up questions which went pretty deep.
  • Walk us through a recent project you led or contributed to significantly. Cover the problem, constraints, timeline, how you estimated work, and how you managed risk.
  • How did you delegate work and coordinate with your teammates during this project?
  • How did your collaboration with your manager differ from how you worked with a peer IC on this project?
  • What were the key technical or product trade-offs you made, and how did you decide between them?
  • How did you handle scope creep during the project?
  • Describe a time you had to re-prioritize under a tight deadline. What got cut and how did you make that call?
  • How did you communicate and align with other teams during the project?
  • What outcomes and success metrics did you use to evaluate the project, and did you hit them?
  • What would you do differently if you ran this project again?
  • Walk us through a conflict that came up during the project and how you resolved it.

“This is the core of the whole round.”

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Plaid·Software Engineer·Onsite - System Design / Architecture

Jul 2026
Plaid data engineering round built around a take-home assignment, where you sit down in a locally configured environment and write SQL while talking through your design decisions out loud. The interviewer then picks apart every choice you made until something breaks.
  • Walk through how you designed the pipeline from raw source data through to the final analytical layer. Why did you structure it the way you did?
  • Star schema or snowflake for this model, and what drove that choice?
  • How would you handle incremental loads for this pipeline? What's your strategy and what are the failure modes?
  • What happens to your model if events arrive out of order or timestamps have timezone inconsistencies?
  • Your pipeline has duplicate rows coming in from the source. How does your model handle that, and where does deduplication live?
  • The source schema changes and a new column gets added, or an existing column gets renamed. How does your pipeline not break?
  • How do you handle deletes in the source system? Does your model support hard deletes, and what are the implications?
  • There are NULLs in your join keys. What does your model do with those rows?

“This was basically the whole interview in one question.”

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Plaid·Software Engineer·Technical Phone Screen

Jun 2026
Plaid data engineering interview that threw a deliberately messy, under-specified data problem at me. The core task was building a fuzzy bank-name mapping pipeline, and the ambiguity was very much the point. Walked away thinking I should have asked more clarifying questions upfront instead of diving straight into code.
  • Write a function that normalizes a raw bank name string into a canonical form, handling varying capitalization, punctuation, abbreviations, and corporate suffixes like 'N.A.', 'Inc.', and 'Corp.'.
  • Given cleaned bank name data with a non-1:1 mapping between internal and external bank IDs, write a fuzzy mapping function that returns all plausible external bank IDs for each internal bank ID rather than a single match.

“This part felt manageable.”

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Plaid·Software Engineer·Onsite - System Design / Architecture

Jun 2026
Plaid software engineer interview that was essentially a full system design presentation. You pick a project you owned and walk through the whole thing on slides, from problem framing to postmortem. More prep-intensive than I expected.
  • Walk through a significant project you owned end-to-end using a slide deck, covering the problem, goals, stakeholders, constraints, architecture, data model, APIs, design decisions, trade-offs, performance and scalability, testing and rollout, metrics, incidents, and lessons learned.

“This is basically a 30-45 minute presentation and they will poke at every layer.”

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Plaid·Software Engineer·Technical Phone Screen

Jun 2026
Plaid SWE interview with a meaty data engineering problem involving routing number deduplication and conflict resolution across multiple JSON sources. The problem had a lot of moving parts and felt more like a mini system design than a pure coding question.
  • You're given bank routing data from multiple JSON sources. Each source has records mapping routing numbers to bank names, but the same bank can appear under different aliases, the same routing number can appear multiple times within a source, and different sources can disagree on which bank a routing number belongs to. Write a function that normalizes bank names using an alias map, produces a final routing-to-canonical-bank mapping, resolves conflicts using majority vote across sources with a tiebreaker based on source priority, and outputs a conflict report listing which routing numbers had disagreements and how the vote went.

“This one took me a few minutes to even parse what was being asked.”

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Plaid·Software Engineer·Technical Phone Screen

Jun 2026
Plaid SWE interview with a coupon-discount coding problem that escalated pretty quickly from a single coupon to multi-coupon stacking with a bunch of edge cases to handle. Clean code, tests, and complexity discussion all expected.
  • You have a shopping cart where each item has a category and a price, plus a list of coupons. First, implement applying a single coupon (fixed discount or percentage off a category) and compute the final total. Then extend it to handle multiple coupons with stacking rules you define. Make sure to handle: discounts exceeding the item price (floor at zero), the same category targeted by multiple coupons, and percentage discounts over 100%. Write tests and discuss time complexity.

“The single-coupon phase felt manageable but I underestimated how much design thinking the multi-coupon part required.”

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Plaid·Software Engineer·Onsite - System Design / Architecture

May 2026
System design round at Plaid for a software engineer role. The prompt was basically 'build ChatGPT' which sounds exciting until you realize how many moving parts they actually want you to cover in 45 minutes.
  • Design a conversational AI assistant similar to ChatGPT. Your design should support multi-turn conversations with history, token-by-token streaming responses, high availability under peak load, safety controls like toxicity filtering and PII handling, and optional tool use such as calling a search API or calculator. Walk through the high-level architecture, key components, storage choices, scaling strategy, and how you'd evaluate quality and safety in production.

“I started with the happy path, which in hindsight was the wrong move.”

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Plaid·Software Engineer·Technical Phone Screen

May 2026
Plaid SWE interview with a meaty algorithmic problem that had more moving parts than I expected. The core idea isn't too bad but they wanted the full package: proof of correctness, complexity analysis, working code, and tests, all in one shot.
  • Given an array of item prices in a checkout line, apply a discount rule where each item's discount equals the price of the first subsequent item that costs less than or equal to it. Return the array of final prices and the total savings. Solve in O(n) time, prove correctness, analyze complexity, and write code with tests.

“I recognized the monotonic stack pattern pretty fast, which was a relief.”

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Plaid·Software Engineer·Technical Phone Screen

May 2026
Plaid data engineering screen, one coding/data problem that looked easy on the surface but had a follow-up that would've wrecked me. The first part was clean enough, the second part (many-to-many mapping) is a whole different beast they save for later.
  • You're given a dataset that maps bank names and identifiers to two ID systems: an internal bank ID and an external bank ID. Write a function that takes this dataset as input and returns a clean mapping from every internal bank ID to its corresponding external bank ID.

“The join logic itself wasn't bad once I clarified the schema upfront, which I actually remembered to do this time.”

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