APIs are the backbone of the modern internet, but integrating with them can often feel like a chore. Writing boilerplate code, handling authentication, and keeping up with API changes takes valuable time away from building core features. This is where an SDK generator tool becomes a developer’s best friend, automating the tedious work of creating client libraries so you can focus on what matters.
This guide will walk you through everything you need to know about using an SDK generator tool, from understanding the basics to comparing popular options and integrating one into your workflow.
Let’s start with the fundamentals. What exactly is this kind of tool, and why is it becoming so essential for modern development teams?
An SDK generator tool is a program that automatically creates a Software Development Kit (SDK) from a machine readable API specification, most commonly an OpenAPI file. Instead of manually writing code to handle HTTP requests, responses, authentication, and data models, the generator does it for you. The output is an idiomatic, ready to use client library in the programming language of your choice, complete with features like request retries, pagination helpers, and proper error handling.
The shift toward API first development is accelerating. In 2024, a survey showed that 74% of organizations have adopted an API first approach. With teams now capable of producing new APIs in under a week, the pressure to provide excellent developer experiences has never been higher.
Yet, the single biggest obstacle developers face when consuming APIs is a lack of documentation. An SDK generator tool directly addresses this by using the API spec as a single source of truth to create both functional SDKs and corresponding documentation, ensuring they never fall out of sync. This automation is no longer a luxury, it’s a necessity for scaling developer adoption.
Not all generators are created equal. Choosing the right one depends on your team’s needs, your API’s complexity, and the level of support you require.
When comparing options, consider these critical factors:
The quality of your generated SDK depends heavily on the generator’s ability to understand your API specification. Modern tools should fully support OpenAPI 3.1, which is 100% compatible with JSON Schema Draft 2020 12. This alignment is crucial for correctly generating code that handles complex data types, validation rules, and polymorphism.
Using an SDK generator tool offers clear advantages, but it’s good to be aware of the tradeoffs.
Pros:
Cons:
The market for SDK generation includes powerful open source projects and sophisticated managed platforms. Here’s a rundown of the key players.
For teams that need more than just code generation, managed platforms offer a complete solution with CI/CD integration, support, and documentation hosting.
Ready to give it a try? The initial process is straightforward and follows a few common steps regardless of the specific tool you choose.
Most command line based generators can be installed in several ways, giving you flexibility for local development and CI/CD environments.
brew install openapi-generator) or npm (npm i -g @openapitools/openapi-generator-cli) for a quick local setup. You can also find wrappers on PyPI for installation via pip.While flags vary between tools, the basic command line syntax is often similar. You’ll typically need to specify three things:
-i)-g)-o)For more advanced control, you can pass a configuration file (-c) to manage numerous options without cluttering your command line. This is where you can define everything from package metadata to custom type mappings. You can also provide your own templates to completely control the structure and style of the generated code, including SDK code snippets in your docs.
Modern code editors can significantly improve your workflow. Extensions for IDEs like VS Code and JetBrains products provide OpenAPI aware features like autocomplete, validation, and live previews. This helps you catch errors in your spec before you even run the SDK generator tool.
Once you move beyond basic generation, the real power of these tools comes from automation and robust testing.
The best practice is to never run a generator manually. Instead, integrate it into your continuous integration and deployment pipeline. You can use platforms like GitHub Actions to automatically trigger the SDK generation process whenever your OpenAPI specification is updated. This ensures that your SDKs and documentation are always in sync with your API. You can also self host an online openapi generator container, which exposes an HTTP API for generating SDKs in CI environments that can’t install Java or other dependencies.
How can you trust the code a machine wrote? By testing it, of course. Several strategies exist for validating generated SDKs:
The founders of Fern experienced the power of internal SDK generation tools at companies like Palantir and Amazon, which inspired them to bring that same power to everyone. The vision extends beyond just improving developer experience (DX). As AI agents become more prevalent, APIs will need to be easily consumable by machines, a concept called Agentic Experience (AX). A high quality SDK generator tool is the first step toward building APIs that are ready for both humans and AI. (You can also add AI‑powered answers to your docs with Ask Fern.)
If your team is struggling to keep SDKs and documentation in sync or your current open source solution isn’t cutting it, it might be time for a managed solution. Book a demo. Platforms like Fern are designed to solve these problems, helping companies like Cohere save hundreds of thousands in engineering costs while shipping more SDKs than ever before.
What is the main benefit of using an SDK generator tool?
The primary benefit is speed and consistency. It automates the creation of client libraries across multiple languages, saving significant engineering time and ensuring that all SDKs are up to date with the latest API changes.
Is OpenAPI Generator the same as Swagger Codegen?
No. OpenAPI Generator was forked from Swagger Codegen in 2018 by the community to accelerate development. While they share a common origin, they are now separate projects with different release cycles and features.
Can I customize the code that an SDK generator tool produces?
Yes. Most open source generators, like OpenAPI Generator, allow for extensive customization through user provided templates, configuration files, and custom properties. Managed platforms also offer various levels of customization.
What’s the difference between an open source and a managed SDK generator tool?
Open source tools give you maximum control and flexibility but require you to manage the setup, customization, and CI/CD integration. Managed tools offer a more streamlined, “batteries included” experience, handling CI, publishing to package registries, and providing enterprise support, but with less granular control.
How do I test an SDK created by a generator?
You can test a generated SDK just like any other code library. Best practices include using contract testing against your OpenAPI spec, property based testing to find edge cases, and mocking HTTP responses to test specific behaviors and error conditions.
