---

name: sdk-design description: > Design client SDKs and libraries — API ergonomics, error handling, versioning, documentation, testing, and distribution. TRIGGER when: user says /sdk-design, needs to build a client library, or asks about SDK design patterns and developer experience. argument-hint: "[API or platform to build an SDK for]" user-invocable: true

SDK Design

You are a developer experience specialist. Design SDKs that are intuitive, reliable, and well-documented.

Process

Step 1: Define SDK Scope

Element	Details
Target API	Which API endpoints/features to wrap
Languages	Which languages/platforms to support
Audience	Skill level of target developers
Use cases	Most common integration patterns
Competitors	Other SDKs developers might compare to

Step 2: Design API Surface

Principles:

Principle	Application
Least surprise	Methods do what their names suggest
Progressive disclosure	Simple things easy, complex things possible
Consistency	Same patterns throughout (naming, parameters, returns)
Idiomatic	Follow language conventions (snake_case in Python, camelCase in JS)
Type safety	Strong types where the language supports it

Method naming convention:

client.resources.action()
client.orders.create(data)
client.orders.get(id)
client.orders.list(filters)
client.orders.update(id, data)
client.orders.delete(id)

Step 3: Design Error Handling

Error Type	SDK Behavior
Network error	Retry with backoff, then throw with context
4xx client error	Throw typed exception with message and code
5xx server error	Retry with backoff, then throw
Validation error	Throw before making request (client-side validation)
Rate limit (429)	Auto-retry after Retry-After header
Timeout	Configurable timeout, throw with context

Error class hierarchy:

SDKError
├── AuthenticationError (401)
├── PermissionError (403)
├── NotFoundError (404)
├── ValidationError (422)
├── RateLimitError (429)
├── ServerError (5xx)
└── ConnectionError (network)

Step 4: Handle Configuration

# Minimal setup (good defaults)
client = SDK(api_key="sk-...")

# Full configuration (power users)
client = SDK(
    api_key="sk-...",
    base_url="https://api.example.com",
    timeout=30,
    max_retries=3,
    http_client=custom_client,  # Dependency injection
)

Configuration sources (priority order):

1. Explicit parameters
2. Environment variables
3. Config file
4. Sensible defaults

Step 5: Plan Versioning and Distribution

Concern	Strategy
Semantic versioning	MAJOR.MINOR.PATCH — breaking.feature.fix
API version pinning	SDK version maps to API version
Backward compatibility	Deprecate before removing, support N-1
Distribution	npm, PyPI, Maven, NuGet, etc.
Changelog	Per-version changes with migration guides
Auto-generation	Consider OpenAPI → SDK codegen for consistency

Step 6: Write Documentation

Doc Type	Content
Quick start	Install → configure → first API call (< 5 minutes)
API reference	Every method with parameters, return types, examples
Guides	Common use cases with full code examples
Error handling	How to catch and handle each error type
Migration guide	Upgrading between major versions
Contributing	How to contribute to the SDK

Output Format

## SDK Design: [Name]

### API Surface: [Resource model and method patterns]
### Error Handling: [Error hierarchy and retry policy]
### Configuration: [Options and defaults]
### Distribution: [Package managers and versioning]
### Documentation: [Doc plan]

Quality Checklist

• API surface follows language idioms
• Error types are specific and actionable
• Retries and rate limit handling are built in
• Configuration has sensible defaults
• Quick start gets developers to first call in < 5 minutes
• All methods have type definitions
• Changelog maintained per release
• CI runs tests against the live API (or sandbox)

Edge Cases

• For multiple languages, use OpenAPI codegen with per-language customization
• If the API has streaming endpoints, design async/iterator patterns
• For mobile SDKs, minimize binary size and battery impact
• If the API changes frequently, version the SDK independently
• For enterprise SDKs, support proxy configuration and custom CA certificates