As developers, we know that Swift app development is all about creating seamless experiences for our users. But what about the experiences of the client developers who are using our software development kits (SDKs)? In this post, we'll dive into the principles and best practices for building SDKs that elevate client developer experience.

Why Do We Need SDKs?

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SDKs come in all shapes and sizes, but when it comes to elevating client developer experience, we're talking about SDKs that enable OS-agnostic development or provide a layer of abstraction over APIs. These types of SDKs are essential for building scalable and maintainable applications.

SDK & Developer Empathy

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As developers ourselves, we know how frustrating it can be when an SDK is difficult to use or doesn't provide the right level of support. That's why developer empathy is crucial in SDK design. A good SDK should be designed with the client developer in mind, providing features that make their lives easier and more enjoyable.

SDK: Guiding Principles

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So what makes a great SDK? Here are some guiding principles to keep in mind:

  • Idiomatic: Design the SDK to feel natural and leverage conventions of its target programming language.
  • Consistent: Ensure terminology and behavior are predictable within the SDK, logically aligned with underlying services (when applicable), and maintainable across client libraries and APIs which the SDK supports.
  • Approachable: Offer documentation (tutorials, samples), sensible defaults for common use cases, and progressive disclosure of advanced features.
  • Diagnosable: Make understanding the SDK's behavior and diagnosing issues straightforward through clear logging, configurable tracing mechanisms (including standard formats like W3C Trace Context), and actionable error messages.
  • Dependable: Prioritize stability, minimize breaking changes, and ensure long-term maintainability by those who will be consuming your SDK.

SDK Development Best Practices

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So how do we apply these principles in our daily work? Here are some best practices to keep in mind:

💡 Empathy & Idiomatic Design

  • Leverage Python idioms—clear docstrings, generators (yield), and language-native features likeasync /await and type hints.
  • Design with popular frameworks in mind (Flask, FastAPI).
  • Consider middleware patterns as think-SDK integrations for auth and security.

🐛 Logging & Tracing

  • Implement robust try/except handling with context-rich exceptions.
  • Adopt standardized tracing strategies (e.g., W3C Trace Context).
  • Use a consistent logging strategy via Python's logging module.
  • Enable configurable logging levels tailored to configurations e.g. debug vs. info.

✅ Testing & Quality

  • Build thorough unit and integration tests.
  • Validate error handling and edge cases.
  • Include tests for versioned APIs, and other versioned schemas for backward compatibility awareness.
  • Support SDK testability by consumers—don't make mocking a nightmare.

🔁 Versioning & Compatibility

  • Follow Semantic Versioning (SemVer) religiously.
  • Be explicit about what is your public API and what is not considered public and can change. Communicate that to your consumers.
  • Announce breaking changes with proper deprecation warnings in SDKs.
  • Use optional dependencies to avoid bloat and dependency hell.

SDK: Generating from Code

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SDK development can be an art—but code generation tools can help accelerate boilerplate and improve consistency. Whether you're crafting a thin wrapper or enriching a thick SDK, here are two key strategies:

🧭 Top-Down (Specification First)

  • Concept: Define domain entities and operations using a specification language, then generate SDKs from that.
  • Tool Example: Typespec—a purpose-built language where you define services in .tspec files and auto-generate clients or servers.

✅ Strengths:

Enables consistent modeling of entities and operations.

Great for deeply integrated SDKs with a strong data model.

❌ Tradeoffs:

Requires learning a new spec language.

Can feel rigid if you want quick manual tweaks.

Adoption is still growing.

🧱 Bottom-Up (Interface Driven)

  • Concept: Start from the API interface itself—usually an OpenAPI/Swagger spec—and generate SDKs based on that.
  • Tool Example: Plenty available. They ingest OpenAPI YAML/JSON and map endpoints, headers, and models to your target language.

✅ Strengths:

Fast and flexible—works across many languages.

Excellent fit for existing APIs where contract comes first.

❌ Tradeoffs:

Doesn’t capture domain semantics beyond the interface.

Requires cleanup to match language idioms.

Code quality varies with spec completeness and tool maturity.