SDKs

There are multiple ways to use Vercel Flags, depending on your framework and how much control you need.

Use the Flags SDK if you're building with Next.js or SvelteKit. It provides the best developer experience with automatic integration for Flags Explorer, precompute for static pages, and framework-specific optimizations.

Use OpenFeature if you need a vendor-neutral API that allows switching between flag providers without code changes, or if you're already using OpenFeature in your stack.

Use the Core Library if you're working outside of supported frameworks, building custom tooling, or need direct access to the evaluation engine.

The Flags SDK and OpenFeature are both provider-agnostic — they don't evaluate flags themselves, but instead delegate to a provider. The @vercel/flags-core library is that provider for Vercel Flags.

The difference between the Flags SDK and OpenFeature is scope. The Flags SDK is designed for specific frameworks like Next.js and SvelteKit, so it can offer deeper integrations like Flags Explorer and precomputation. OpenFeature is a broader standard that works across languages and frameworks, but leaves those framework-specific capabilities to you.

Both have adapters that connect them to @vercel/flags-core: @flags-sdk/vercel for the Flags SDK, and @vercel/flags-core/openfeature for OpenFeature.

All integration methods use the same environment variables:

• FLAGS: Connection string that identifies your Vercel Flags project. Vercel automatically sets this with different values for Production, Preview, and Development environments.
• FLAGS_SECRET: Secret key used by Flags Explorer for secure overrides. Required if you want to use Flags Explorer.

When you create your first flag in the Vercel Dashboard, these variables are automatically added to your project.

• Get started with the Flags SDK
• Learn about OpenFeature integration
• Use the core library directly