#extensibility

6 extensibility interview questions, asked at Amazon, Cursor, Google and 4 more companies. Last asked Oct 2026.

Merge two config trees with per-node merge rulesCodingTwo configuration files have been parsed from YAML into trees of dicts, lists and plain values: a base and an overlay. Merge the overlay into the base. Each node can carry its own…
Last asked Oct 2026
Extensible chat app with command botsCodingImplement an in-memory chat app with one shared channel that people and bots post to. Users send text. Some messages are slash commands (/name arg ...), and bots can respond to…
Last asked Oct 2026
JSON merge API with pluggable merge behaviorsCodingDesign and implement a function that merges two JSON documents, where the way conflicts are resolved is pluggable: for example, how two objects, two arrays or two different scalar…
Last asked Aug 2026
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Pluggable hierarchical rate limiterCodingDesign a rate limiter with hierarchical limits (user, team, global) whose limit rules are pluggable without changing the core. Reported on 1point3acres' Cursor bank; reconstructed…
Last asked Feb 2026
Extensible employee cost calculatorOO designDesign the classes for a calculator that works out what employees cost the company. Different kinds of employees are costed differently, and new kinds or cost components will be…
Last asked Feb 2026
Integer to English words, built up by rangeCodingWrite a function that spells out an integer in English words. The interviewer adds the ranges in parts, and later parts should reuse earlier ones, so design for extension from the…