#api design

21 api design interview questions, asked at Microsoft, Google, Snowflake and 8 more companies. Last asked Sep 2026.

Design an API to deep-copy a dataset with its tasks, responses and gradesSystem designYour application stores datasets. A dataset contains tasks, each task has model responses, and each response has grades. Design an API that copies a dataset with all its tasks…
Last asked Sep 2026
Extensible spreadsheet range aggregatesCodingDesign a spreadsheet API with getsum, getmax and getmin over a range of cells. A cell holds either a number or a formula, and an aggregate must read every cell's computed value…
Last asked Sep 2026
Design versioned IDE settings for users and teamsSystem designDesign the service that stores a code editor's settings for users and teams. A user's setup follows them to every machine, a user can belong to several teams, and each team sets…
Last asked Sep 2026
Fewest clicks between two wiki pagesCodingWiki pages link to other pages. Given a start URL and a target URL, find the fewest clicks needed to get from the start to the target, and one shortest path of URLs, or report…
Last asked Sep 2026
Generic retry helper with configurable backoffCodingCalls to remote services fail now and then for reasons that go away on their own: a dropped connection, a busy server, a timeout. Write a generic retry helper that runs a…
Last asked Aug 2026
JSON merge API with pluggable merge behaviorsCodingDesign and implement a function that merges two JSON documents into a new one, without changing either input. Objects merge key by key, recursively. The caller chooses how arrays…
Last asked Aug 2026
Design a to-do list service: CRUD, auth, rate limits, caching, versioningSystem designDesign the backend for a multi-tenant to-do list app: users create, read, update and delete tasks; requests are authenticated; clients are rate limited; reads are cached; and the…
Last asked Jun 2026
Last-click attributionCodingAn ad platform credits each conversion (a purchase, a sign-up) to the last ad the user clicked before converting. Implement the in-memory APIs that record clicks and, when a user…
Last asked May 2026
Design a low-latency product price update APISystem designDesign an API and serving system for product prices. Each product's price changes at most once every 24 hours, but a product launch page must read prices for many products at…
Last asked Apr 2026
Design a daily puzzle platformSystem designDesign the backend of a daily puzzle platform: every day one new puzzle goes live for all users, who try to solve it, get a score, and see how they compare with others. Think of a…
Last asked Apr 2026
Insert documents and check them against boolean predicatesCodingBuild a small in-memory document service. Documents are text, identified by filename. A predicate is a boolean expression over terms; a term is true when that exact word appears…
Last asked Apr 2026
Implement team-style business logic with OOP, then roll out an API changeCodingA practical backend round in two parts. First, the interviewer describes a piece of business logic like what the team builds and asks you to implement it in an existing backend…
Last asked Apr 2026
Design a secure API for an AI assistantSystem designDesign the API for an enterprise AI assistant that many separate organizations (tenants) use. Signed-in users send prompts and get responses; the assistant can call…
Last asked Apr 2026
Polynomial multiplication API in CCodingDesign and implement a small C API for polynomials with integer coefficients: a type, functions to create and free a polynomial, and a function that multiplies two polynomials and…
Last asked Feb 2026
Design REST APIs for storing JSON filesSystem designDesign the REST API and the backend for a service that stores and serves JSON documents for many users and applications: create, read, update (whole or partial) and delete…
Last asked Jan 2026
Implement an event emitterCodingImplement a small event emitter for a frontend codebase, like the one in Node or in many UI libraries. Code subscribes handlers to named events and other code emits those events…
Last asked Jan 2026
Design CRUD APIs backed by asynchronous jobsSystem designDesign a backend service that exposes create, read, update and delete APIs for a resource, where some operations start long-running work that cannot finish inside the request…
Last asked Jan 2026
Design the APIs of an executable notebook serviceSystem designDesign a collaborative code notebook service: users edit notebooks in the browser, an execution service runs code, and a proxy fetches execution results and streams them back to…
Last asked Sep 2025
Design a watch history and resume-playback serviceSystem designDesign the service behind a video platform's watch history: it records which titles each user watched and how far they got, so playback resumes at the right point on any device…
Last asked Sep 2025
Keep a shared payment account correct under concurrent paymentsSystem designTwo people share one online payment account and both pay with it at the same moment. Design the payment flow so the balance is never wrong: no double spending, no lost updates, no…
Last asked Jul 2025
Ship a breaking API change to a library communityBehavioral"Tell me about a time you had to make a breaking change to a public API that many people depend on. How did you plan the migration, how was the rollout staged, and how did you…