generating-api-sdks

Generating API SDKs

Overview

Generate type-safe client SDKs in multiple languages (TypeScript, Python, Go, Java) from OpenAPI 3.0+ specifications. Produce idiomatic client libraries with authentication handling, automatic retries, pagination helpers, and comprehensive type definitions that mirror the API contract.

Prerequisites

• OpenAPI 3.0+ specification file (YAML or JSON) with complete schema definitions
• Target language toolchain installed (Node.js/TypeScript, Python 3.10+, Go 1.21+, or Java 17+)
• OpenAPI Generator CLI or equivalent code generation tool
• Package registry credentials for publishing (npm, PyPI, Maven Central, pkg.go.dev)
• CI pipeline for automated SDK builds on spec changes

Instructions

1. Read and validate the OpenAPI specification using Read, checking for complete schema definitions, proper $ref usage, and response type coverage across all endpoints.
2. Extract all operation IDs, request/response models, and authentication schemes from the specification to build the SDK method inventory.
3. Generate typed model classes for every schema component, including nested objects, enums, and discriminated unions with proper nullability annotations.
4. Create a client class with methods for each API operation, mapping operation IDs to idiomatic method names (e.g., listUsers, get_user, CreateUser).
5. Implement authentication handling with support for Bearer tokens, API keys (header and query), and OAuth2 client credentials flow, configurable at client instantiation.
6. Add automatic retry logic with exponential backoff for 429 and 5xx responses, with configurable max retries and backoff multiplier.
7. Build pagination helpers that abstract cursor-based and offset pagination into iterator/generator patterns native to each target language.
8. Generate comprehensive JSDoc/docstring/Javadoc comments from OpenAPI description and summary fields for full IDE IntelliSense support.
9. Create a test suite that validates SDK methods against a mock server running the OpenAPI spec, covering authentication, error handling, and pagination.

See ${CLAUDE_SKILL_DIR}/references/implementation.md for the full implementation guide.

Output

• ${CLAUDE_SKILL_DIR}/sdk/typescript/src/client.ts - Main SDK client class with typed methods
• ${CLAUDE_SKILL_DIR}/sdk/typescript/src/models/ - TypeScript interfaces and type definitions
• ${CLAUDE_SKILL_DIR}/sdk/python/client.py - Python SDK with dataclass models and async support
• ${CLAUDE_SKILL_DIR}/sdk/go/client.go - Go SDK with struct types and context-based methods
• ${CLAUDE_SKILL_DIR}/sdk/*/README.md - Per-language installation and usage documentation
• ${CLAUDE_SKILL_DIR}/sdk/*/tests/ - SDK test suites per language

Error Handling

Error	Cause	Solution
Schema generation failure	OpenAPI spec contains $ref cycles or missing component definitions	Run spec linting with spectral first; resolve circular references with allOf composition
Type mismatch	API response does not match generated model types at runtime	Add runtime response validation option; log schema drift warnings for API provider notification
Auth configuration error	SDK instantiated without required credentials for protected endpoints	Throw descriptive error at client construction time listing required auth parameters
Pagination exhaustion	Iterator consumes all pages without termination condition	Enforce maximum page count safety limit; detect empty result sets as termination signal
Rate limit handling	SDK retry logic conflicts with application-level retry logic	Expose retryConfig option to disable built-in retries; emit retry events for observability

Refer to ${CLAUDE_SKILL_DIR}/references/errors.md for comprehensive error patterns.

Examples

TypeScript SDK for payment API: Generate a fully typed PaymentsClient with methods like createCharge(amount, currency) returning Promise<Charge>, automatic Bearer token injection, and paginated listTransactions() returning an async iterator.

Python SDK with async support: Produce both sync (PaymentsClient) and async (AsyncPaymentsClient) clients using httpx, with Pydantic models for request/response validation and __aiter__ pagination support.

Multi-language CI pipeline: On OpenAPI spec change, automatically regenerate SDKs in all target languages, run tests against a mock server, bump semantic versions, and publish to respective package registries.

See ${CLAUDE_SKILL_DIR}/references/examples.md for additional examples.

Resources

• OpenAPI Generator: https://openapi-generator.tech/
• Speakeasy SDK generation: https://speakeasy.com/
• Microsoft Kiota for API client generation
• OpenAPI Specification 3.1: https://spec.openapis.org/oas/v3.1.0