Hey API is an open-source platform and code generation engine designed to transform OpenAPI specifications into production-grade API infrastructure. Created to serve as a comprehensive, high-quality solution for modern engineering teams, it eliminates the need for maintaining handwritten API interfaces or manual boilerplate code. By leveraging OpenAPI as a single source of truth, Hey API provides a deterministic and efficient way to bridge the gap between API specifications and client-side implementation. The project focuses on quality, speed, and workflow integration, aiming to be a permanent, reliable standard for developers building scalable API layers.

Functionality centers on parsing OpenAPI specification files and generating fully typed SDK clients, data models, and API integrations. The tool operates through a modular, plugin-based architecture, allowing developers to select only the components they require for their specific project needs. Whether defining APIs from scratch or integrating existing specifications, the engine produces consistent, high-quality output that can be easily integrated into CI/CD pipelines to ensure that client code remains synchronized with backend changes.

Some of the key features are:

• Typed SDK Clients: Automatically generates fully typed SDKs that reduce manual effort and maintain strict synchronization with API specifications.
• Plugin Ecosystem: Offers over 20 composable plugins, including support for Zod and Valibot for runtime validation, and TanStack Query for state management.
• Broad Framework Support: Provides native support for various runtime environments and frameworks, including Fetch API, Axios, Angular, Next.js, and Nuxt.
• Deterministic Output: Ensures identical, reliable code output every time the generator is run against a specific API specification.
• Customizable Extensibility: Allows developers to build custom plugins and clients using the same robust internal APIs that power the core tool.

Operation is streamlined through a single configuration file and a simple command-line interface. Developers provide an OpenAPI specification—whether a local file, a remote URL, or a registry shorthand—and configure the desired output and plugins. Once defined, the generator can be executed via CLI, integrated into a Node.js build process, or plugged directly into a Vite development pipeline. Every time the underlying API specification is updated, the developer can regenerate the infrastructure, ensuring that the client-side code automatically reflects the latest API schema changes without introducing inconsistencies.

Some common use cases include:

• Frontend Client Generation: Quickly bootstrap frontend applications by generating type-safe API clients that significantly reduce the amount of boilerplate code required to interact with backend services.
• Continuous Integration Workflows: Integrate the code generation process directly into CI/CD pipelines to automatically update client interfaces whenever backend API specs change, preventing drift between the client and server.
• Runtime Validation: Use generated schema plugins like Zod to perform automatic, high-performance runtime data validation, ensuring that responses from the API conform to the expected structures.
• State Management Integration: Leverage built-in plugins for TanStack Query to handle API requests, caching, and state synchronization within complex web applications efficiently.