# How can I make my library compatible with the Vercel Edge Runtime?

**Author:** Lee Robinson

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This guide will help make your npm package or SDK compatible with the [Edge Runtime](https://vercel.com/docs/functions/runtimes/edge), a lightweight subset of Node.js. Edge Runtime compatibility is useful when maintaining existing Edge Runtime code or building code used by [Routing Middleware](https://vercel.com/docs/routing-middleware). For new Vercel Functions, use the Node.js runtime by default.

This guide will cover the supported and unsupported APIs and library recommendations.

- [Benefits](#benefits-of-the-edge-runtime)
  
- [Supported APIs](#supported-apis)
  
- [Unsupported APIs](#unsupported-apis)
  
- [Library Recommendations](#library-recommendations)
  
- [Checking Edge Runtime](#checking-edge-runtime)
  

## Benefits of the Edge Runtime

Benefits of adopting the Edge Runtime for your library include:

- Built on Web standard APIs and compatible with many Node.js APIs
  
- Interoperability with every runtime environment, including the client, server, and edge
  

## Supported APIs

The Edge Runtime provides a subset of Web APIs such as `**fetch**`, `**Request**`, and `**Response**`. This lightweight API layer is built to be performant and execute code with minimal latency.

For a complete list of supported APIs, please refer to the [Edge Runtime documentation](https://vercel.com/docs/functions/runtimes/edge).

## Unsupported APIs

The Edge Runtime has some restrictions:

- Some Node.js APIs other than the ones listed in the documentation are not supported. For example, you can't read or write to the filesystem.
  
- `**node_modules**` can be used, as long as they implement ES Modules and do not use native Node.js APIs.
  
- Calling `**require**` directly is not allowed. Use `**import**` instead.
  

The following JavaScript language features are disabled, and will not work:

- `**eval**`
  
- `**new Function(evalString)**`
  
- `**WebAssembly.compile**`
  
- `**WebAssembly.instantiate**`
  

## Library Recommendations

To ensure compatibility with the Edge Runtime, consider using the following alternatives to libraries or APIs that aren't compatible:

- For data fetching, prefer using the Web `**fetch**` API instead of `**axios**` or `**cross-fetch**`.
  
- For authentication, prefer using `**node-jose**`.
  
- For ID generation, prefer using `**nanoid**`.
  

The following AI providers SDKs are compatible with the Edge Runtime:

- [Anthropic](https://sdk.vercel.ai/docs/guides/providers/anthropic)
  
- [Cohere](https://ai-sdk.dev/providers/ai-sdk-providers/cohere)
  
- [Hugging Face](https://sdk.vercel.ai/docs/guides/providers/huggingface)
  
- [LangChain](https://ai-sdk.dev/providers/adapters/langchain)
  
- [OpenAI](https://sdk.vercel.ai/docs/guides/providers/openai)
  
- [Replicate](https://ai-sdk.dev/providers/ai-sdk-providers/replicate)
  

## Checking Edge Runtime

You can check if your function is running on the Edge Runtime by checking the global `**globalThis.EdgeRuntime**` property. This can be helpful if you need to validate that your function is running on the Edge Runtime in tests or if you need to use a different API depending on the runtime.

`if (typeof EdgeRuntime !== 'string') { // Dead-code elimination is enabled for the code inside this block }`

By following this guide and adapting your library or SDK to be compatible with the Edge Runtime, you can support existing Edge Runtime code and Routing Middleware without relying on Node.js-only APIs.

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[View full KB sitemap](/kb/sitemap.md)