Stainless turns an OpenAPI spec into the developer experience layer of an API business: robust, idiomatic SDKs in TypeScript, Python, Go, Java, Kotlin, Ruby, C#, PHP and Terraform; documentation that stays in sync with the API; and state-of-the-art MCP servers so AI agents can consume the API directly. Its codegen pipeline continuously regenerates libraries as the spec evolves, keeping every language current without hand-maintenance.
The team behind the biggest AI SDKs
Founder Alex Rattray previously built Stripe's patented SDK codegen system, and Stainless now generates the official client libraries for OpenAI, Anthropic, Meta, Cerebras and Runway among hundreds of customers — meaning millions of developers install Stainless-generated SDKs every week. The MCP server product extends the same rigor to agent tooling, generating spec-faithful tool definitions for LLMs.
Funding
Based in New York and founded in 2021, Stainless raised a $25M Series A led by Andreessen Horowitz in December 2024, bringing total funding to $35M with backing from Sequoia and angels at MongoDB and Zapier. A free tier lets small API teams generate their first SDK before moving to paid plans.