I started with the developer use case, like what does someone actually need to send a text programmatically, and worked outward from there.
Start by clarifying the core user needs and constraints for an SMS API, then outline the primary resources (messages, phone numbers, accounts) and their relationships. Walk through the key endpoints (send, retrieve, list, update) and the critical decisions around authentication, rate limiting, delivery status, and error handling. Emphasize trade-offs and how you'd prioritize features for an MVP versus future iterations.
Pro tip: Anchor your design in real-world developer experience: show how you'd make the API intuitive, consistent, and well-documented, and discuss how you'd handle edge cases like message delivery failures and compliance (e.g., opt-outs, international regulations).
Ask questions to understand the target users (developers, businesses), core use cases (transactional vs. marketing SMS), and constraints (scale, compliance, latency). Define what 'SMS API' means for Twilio: sending, receiving, managing numbers, etc.
List the primary entities: Message, PhoneNumber, Account, and possibly Subaccount, Media (for MMS). Define their attributes and relationships (e.g., a Message belongs to an Account and is sent from a PhoneNumber).
Map CRUD operations to RESTful endpoints: POST /Messages to send, GET /Messages/{sid} to retrieve, GET /Messages to list with filters, and possibly DELETE for redaction. Include endpoints for managing phone numbers and accounts.
Decide on authentication (API keys, OAuth), rate limiting, idempotency, pagination, error formats, webhooks for delivery status, and versioning. Discuss trade-offs (e.g., synchronous vs. asynchronous sending, long-polling vs. webhooks).
Propose an MVP with essential endpoints and features, then outline future enhancements like bulk sending, scheduling, and analytics. Explain how you'd measure success and gather developer feedback.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.