A good model can still fail in the product if the API is hard to use. The interface is where reliability, safety, and usability meet.
Core Principles
- Simplicity: Minimize required parameters and provide sensible defaults
- Clarity: Consistent naming, clear docs, predictable behavior
- Robustness: Validate inputs early and return actionable errors
- Versioning: Plan change management and deprecation from day one
Essential Features
Input Validation: Check types, ranges, and required fields before passing to the model.
Batch Endpoints: Allow multiple samples per request for efficiency.
Async Support: For long-running operations, return a job ID and let clients poll.
Error Handling Strategy
- Separate client errors (400) from server errors (500)
- Provide stable error codes and human-readable messages
- Include actionable metadata (fields, constraints, request IDs)
Monitoring and Observability
- Latency percentiles (p50, p95, p99)
- Error rate by type
- Cost per prediction/request
- Quality signals tied to outcomes
Pro tip: Design the API as if you were the first customer. If it's confusing for you, it will be confusing for everyone.