Fern generates SDKs and API documentation that companies are proud to share with their customers. Since launching in 2023, we’ve been trusted by over 150 customers, including industry leaders like Square, Webflow, ElevenLabs, LaunchDarkly, and Intercom, to power their developer and agent experiences.
Today we’re announcing our $9M Series A, led by Bessemer Venture Partners with participation from Y Combinator, bringing our total funding to $13M.
"The explosion of AI-powered developer platforms has created an urgent need for faster, frictionless integration. By eliminating friction from the developer experience and managing the gritty engineering work that is building and maintaining SDKs and docs, Fern has established itself as a trusted enterprise partner." - Lindsey Li, Vice President at Bessemer Venture Partners.
For companies with public APIs, a great developer experience hinges on two things: SDKs and documentation. While companies like Stripe invest in dedicated developer experience teams, most can’t. Fern levels the playing field by making world-class SDKs and API docs accessible to every company.
Fern is the 2-in-1 solution for SDKs and Docs
“We used to manage separate vendors for our SDKs and Docs, creating unnecessary complexity. Fern consolidates both, streamlining procurement and ensuring a consistent, high-quality developer experience.” - Piotr Dabkowski, CTO at ElevenLabs
SDKs and Docs are like peanut butter and jelly. While each is valuable on its own, the real magic is using them together. Developers expect the methods and parameters in the SDK to be thoroughly documented so they can learn about the API from the comfort of their IDE. For the more complex concepts, these inline comments in the SDK should link out to the documentation website. At the same time, developers expect the API Docs site to have SDK code samples that are always up-to-date - ideally with their API token pre-populated. By powering both the SDK Generation and the API Documentation, Fern is uniquely positioned to deliver a unified developer experience.
SDKs in minutes, not months
“We evaluated multiple SDK providers, and Fern stood out for its code quality. Now, developers use our idiomatic SDKs to move money faster and with less friction.” - John Fellman, Head of Engineering, Developer Platform at Square
When integrating with an API, developers expect an SDK in the language their application is built in. However, building and maintaining SDKs that respect the idioms of each language is difficult and expensive, especially as languages evolve and new languages gain popularity. Fern generates SDKs in TypeScript, Python, Go, Java, C#, PHP, and Ruby, with several more in development. The Fern SDK Generator allows companies to automate the tedious work of building and maintaining SDKs in all popular languages. As input, Fern supports OpenAPI, AsyncAPI or gRPC, and can publish SDKs directly to GitHub and to package registries like npm and PyPI.
Docs that match your brand
“We used to dedicate engineers to maintain our docs infrastructure. Fern migrated 700+ pages of content and freed up our team to focus on building our core product.” - Matt Makai, VP of Developer Experience at LaunchDarkly
Fern Docs enables companies to build beautiful and highly-customizable documentation websites. With its extensive styling options and support for custom JS/CSS/React, any company can build a docs website that seamlessly matches its existing brand. Under the hood, the docs are powered by MDX and can be checked-in to git, and Fern’s GitHub integration makes it easy to preview changes before they go live.
The crown jewel of any Fern Docs website is the API Reference. Auto-generated from a single API spec (OpenAPI, AsyncAPI, or gRPC), the API Reference allows developers to quickly understand the API. For every endpoint, Fern shows copy-paste-ready code examples.
The API reference also includes a fully-featured playground that developers can use to interact with the API without even leaving the page. For companies that also use Fern to generate SDKs, the playground shows a dynamically-generated SDK code snippet that is equivalent to the current request.
The shift from developer experience (DX) to agent experience (AX)
Looking ahead, API calls made by AI will outnumber those made by human developers, shifting the focus from DX to AX. The next wave of integrations will be powered by AI agents. Just as a great developer experience redefined how human developers interact with an API, Fern is defining what API integrations look like for AI agents.
SDKs
- Agent-Optimized SDKs: Fern’s generated SDKs are designed for both human developers and AI agents. Built-in guardrails like inline documentation and strong type safety minimize AI hallucinations, much like how providing an LLM with JSON Schema ensures structured, predictable outputs.
- AI Integration Assistant: Developers and AI agents get instant, precise answers at every stage—from onboarding to authentication to troubleshooting. Trained on your API docs, SDKs, tutorials, and example apps, it ensures accuracy and reduces support overhead.
- Autonomous Integrations: Moving beyond documentation and SDKs, the future of API integrations will involve AI agents that can evaluate API providers, acquire API credentials, generate integration code, and adapt to API changes automatically—minimizing developer effort.
Docs
- /llms.txt: While humans enjoy visually enhanced HTML sites, AI agents prefer a streamlined, token-efficient format. Every Fern Docs website includes an LLM-friendly version, adhering to the /llms.txt protocol, ensuring agents can efficiently learn about an API without distractions like CSS or animations.
- AI-Powered Code Snippet Audits: Fern automatically scans documentation for manually added code snippets and runs tests to ensure they compile, run, and work as described. This AI-driven auditing process helps catch outdated or broken examples, ensuring developers and AI agents always have reliable, executable code.
Join us
If you're passionate about open source, developer tools, and the future of API integrations, join us. We’re hiring frontend engineers, backend engineers, deployed engineers, and technical account executives to help shape the future of API integrations. Our team works together in our office in Brooklyn, NY.
There’s a lot to build, and we’re just getting started.