Runtime Cache

# Vercel Runtime Cache API

You are an expert in the Vercel Runtime Cache — an ephemeral caching layer for serverless compute.

## What It Is

The Runtime Cache is a **per-region key-value store** accessible from Vercel Functions, Routing Middleware, and Builds. It supports **tag-based invalidation** for granular cache control.

- **Regional**: Each Vercel region has its own isolated cache
- **Isolated**: Scoped per project AND per deployment environment (`preview` vs `production`)
- **Persistent across deployments**: Cached data survives new deploys; invalidation via TTL or `expireTag`
- **Ephemeral**: Fixed storage limit per project; LRU eviction when full
- **Framework-agnostic**: Works with any framework via `@vercel/functions`

## Key APIs

All APIs from `@vercel/functions`:

### Basic Cache Operations

```ts
import { getCache } from '@vercel/functions';

const cache = getCache();

// Store data with TTL and tags
await cache.set('user:123', userData, {
  ttl: 3600,                      // seconds
  tags: ['users', 'user:123'],    // for bulk invalidation
  name: 'user-profile',           // human-readable label for observability
});

// Retrieve cached data (returns value or undefined)
const data = await cache.get('user:123');

// Delete a specific key
await cache.delete('user:123');

// Expire all entries with a tag (propagates globally within 300ms)
await cache.expireTag('users');
await cache.expireTag(['users', 'user:123']); // multiple tags
```

### Cache Options

```ts
const cache = getCache({
  namespace: 'api',                    // prefix for keys
  namespaceSeparator: ':',             // separator (default)
  keyHashFunction: (key) => sha256(key), // custom key hashing
});
```

### Full Example (Framework-Agnostic)

```ts
import { getCache } from '@vercel/functions';

export default {
  async fetch(request: Request) {
    const cache = getCache();
    const cached = await cache.get('blog-posts');

    if (cached) {
      return Respons