---

name: devex-sdk-design description: Developer experience (DX) engineering, SDK design patterns, API ergonomics, CLI tooling design, documentation-driven development, and developer onboarding. Use when designing SDKs, improving API ergonomics, building developer tools, or creating developer documentation.

Developer Experience & SDK Design

SDK Design Principles

API Ergonomics

// Bad: too many required params, unclear ordering
createUser(name, email, role, true, false, null, 'active');

// Good: builder pattern with named properties
const user = await sdk.users.create({
  name: 'Alice',
  email: 'alice@example.com',
  role: 'admin',
});

// Good: fluent API for complex operations
const results = await sdk.query('users')
  .where('role', '=', 'admin')
  .orderBy('createdAt', 'desc')
  .limit(10)
  .execute();

Progressive Disclosure

// Simple case: just works with defaults
const client = new MySDK('api-key');
const result = await client.doThing();

// Advanced case: full control available
const client = new MySDK({
  apiKey: 'api-key',
  baseUrl: 'https://custom.endpoint.com',
  timeout: 30000,
  retries: { maxAttempts: 3, backoff: 'exponential' },
  middleware: [loggingMiddleware, authRefreshMiddleware],
});

Error Design

// SDK errors should be structured and actionable
class SDKError extends Error {
  constructor(
    message: string,
    public readonly code: string,        // machine-readable
    public readonly statusCode?: number,  // HTTP status if applicable
    public readonly retryable: boolean = false,
    public readonly docs?: string,        // link to relevant docs
  ) {
    super(message);
  }
}

// User sees:
// SDKError: Rate limit exceeded (rate_limit_exceeded)
//   Retryable: true, retry after 2.3s
//   Docs: https://docs.example.com/rate-limits

CLI Design

Command Structure

mycli <command> <subcommand> [flags]

mycli init                    # Interactive setup
mycli deploy --env production # Explicit flags
mycli logs --follow           # Streaming output
mycli config set key value    # Noun-verb pattern

CLI Best Practices

• Sensible defaults: Work out of the box, --flag for customization
• Progressive output: Spinners for long ops, --verbose for debug, --json for machines
• Confirmation prompts: Destructive actions require --yes or interactive confirm
• Shell completion: Generate for bash/zsh/fish/PowerShell
• Exit codes: 0 = success, 1 = error, 2 = usage error

Documentation-Driven Development

README Structure (for SDKs)

1. One-liner: What it does in one sentence
2. Quick start: Copy-paste working example (< 10 lines)
3. Installation: Package manager commands
4. Usage: Common patterns with code examples
5. API reference: Auto-generated from types/docstrings
6. Error handling: Common errors and solutions
7. Migration guide: Breaking changes between versions

Code Examples

• Every public method needs a usage example
• Examples must compile/run — test them in CI
• Show the happy path first, then edge cases
• Include expected output in comments

Developer Onboarding Metrics

• Time to Hello World: < 5 minutes from docs to working code
• Time to first API call: < 10 minutes including auth setup
• Copy-paste success rate: Quick start examples work on first try
• Error resolution time: Error messages lead directly to fix

Versioning & Breaking Changes

• Semantic versioning strictly followed
• Deprecation warnings 2 minor versions before removal
• Migration codemods for major version upgrades
• Changelog with every release (keep-a-changelog format)