Fern vs Stainless: which SDK generator is better? (January 2026)

Fern and Stainless are tools for generating client libraries from API specifications, each offering distinct advantages depending on a team's needs and technical requirements. Fern is a CLI-first tool that supports SDK generation in over nine programming languages, accommodates various protocols including REST, WebSockets, and gRPC, and integrates directly into CI/CD pipelines with version-controlled YAML configuration files. It provides a comprehensive documentation platform with features like an API Explorer and AI-powered search and offers on-premise deployment options for compliance-sensitive industries. In contrast, Stainless is a cloud-based platform that supports SDK generation for eight languages, focusing primarily on REST APIs via a dashboard-driven workflow. While it automates versioning and integrates with package registries, its documentation and customization options are less mature compared to Fern. The choice between Fern and Stainless largely depends on the required protocol flexibility, deployment preferences, and whether the team prioritizes a streamlined dashboard interface or extensive CI/CD integration and on-premise capabilities.