Feature Flag SDK

System DesignStripeLast reported May 2026Medium Frequency

Reported: 8× across candidate reports
First seen: February 2025
Last reported: May 2026
Reported outcome: mixed

Problem Overview

Design a feature flag system / SDK for internal use by engineers. The core API exposes one or two methods: 1. get(String featureKey) → boolean — returns whether a flag is enabled. 2. get(String featureKey, String jsonContext) → boolean (or flag.is_on(name, {user, product})) — returns whether the flag is enabled…

1 candidate-reported follow-up — the exact probes interviewers asked, with the trigger for each
The rest of the problem statement — full requirements, constraints, and edge cases
Approach and trade-offs — what passing candidates did, and the mistakes that sink people

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Verified Source

Every question is reconstructed from multiple independent candidate reports. Verbatim follow-ups, not invented ones.

Codex Fact-Checked

Technical claims, formulas, and scale numbers are reviewed against primary sources.

Interviewer Follow-ups

The exact follow-ups reported by candidates, with the trigger that prompts each one — plus the mistakes that sink people.