Stripe·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Apr 2026

Summary

Stripe coding round for a software engineer role, one problem the whole time. The algorithm wasn't the hard part, the I/O parsing was.

Questions Asked (1)

Implement a subscription email notification system: given users, their subscription data, and a stream of events (new content, billing, etc.), determine which users should receive email notifications and output the results in the required format.

Algorithms & Data StructuresAPI & Integrations

Author's notes

The logic for figuring out who gets emailed wasn't that bad once I mapped it out.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the requirements and defining the data models for users, subscriptions, and events. Then design an event-driven pipeline that filters users based on subscription preferences and event types, and finally formats the output as specified. Discuss trade-offs between batch and real-time processing, and consider scalability and idempotency.

Pro tip: Emphasize idempotency and failure handling: in a billing system like Stripe, duplicate notifications or missed events can be costly, so design with retries and deduplication in mind. Also, mention how you would test the system with edge cases like expired subscriptions or concurrent events.

1. Clarify Requirements and Data Models

Ask questions to understand the exact input/output formats, event types, subscription states, and notification preferences. Define clear schemas for users, subscriptions, and events.

2. Design the Notification Logic

Determine the rules for which users should be notified for each event type, considering subscription status, user preferences, and event relevance. Outline a decision matrix or filtering pipeline.

3. Choose an Architecture and Data Flow

Decide between batch processing (e.g., periodic job) and stream processing (e.g., Kafka, webhooks). Describe how events flow through the system, how users are matched, and how notifications are generated.

4. Address Scalability and Reliability

Discuss partitioning, caching, rate limiting, and idempotency to handle large volumes and ensure exactly-once or at-least-once delivery. Mention monitoring and alerting.

5. Define Output and Testing Strategy

Specify the output format (e.g., list of user IDs, email payloads) and outline unit, integration, and end-to-end tests, including edge cases like expired subscriptions or duplicate events.

Key Points to Mention

Event-driven architecture and message queues (e.g., Kafka, RabbitMQ) for scalability
Idempotency and deduplication to avoid duplicate notifications
Subscription state management (active, past_due, canceled) and user preferences
Batch vs. real-time processing trade-offs
Data modeling for users, subscriptions, and events
Testing strategies including edge cases and failure scenarios

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.