System Design: Webhook Delivery Service

System DesignOpenAILast reported February 2026Medium Frequency
Reported
8× across candidate reports
First seen
May 2025
Last reported
February 2026
Reported outcome
mixed

Problem Overview

Design a scalable Webhook delivery service. Users register a callback URL paired with an eventId. Whenever that eventId is triggered, the system must call the registered callback address with a specific payload. Constraints: each eventId maps to exactly one unique callback address (one-to-one mapping). The system must handle up to…

  • 5 candidate-reported follow-ups — 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.
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