runtime-cache

Work something out once — a slow call to another company's API, a heavy database query — and every later request in that part of the world gets the stored answer instead of doing the work again.

WHEN TO USE

SCOPE

USE FOR

Cache an expensive API response so every function in a region can reuse it.
Clear a whole batch of cached data the moment a CMS webhook fires.
Cut database load for data that many requests read over and over again.
Share computed data between functions in the same region instead of recomputing it.

NOT FOR

Full-page rendering caches — that belongs to Next.js Cache Components instead.
Long-term persistent storage — use a database such as Neon or Upstash instead.
Caching a full response at the CDN — use Cache-Control headers instead.
Keeping state consistent across multiple regions — use a database instead.

This is a saved copy of the skill's SKILL.md instructions. It may differ from the upstream file or the version you install.

In this document (12)

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 deployment environment (preview vs production); scoped per project on Pro/Enterprise, but shared across all projects on a Hobby team
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

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 null)
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

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

Full Example (Framework-Agnostic)

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

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

    if (cached) {
      return Response.json(cached);
    }

    const posts = await fetch('https://api.example.com/posts').then(r => r.json());

    await cache.set('blog-posts', posts, {
      ttl: 3600,
      tags: ['blog'],
    });

    return Response.json(posts);
  },
};

Tag Expiration from Server Action

'use server';
import { getCache } from '@vercel/functions';

export async function invalidateBlog() {
  await getCache().expireTag('blog');
}

CDN Cache Purging Functions

These purge across all three cache layers (CDN + Runtime Cache + Data Cache):

import { invalidateByTag, dangerouslyDeleteByTag } from '@vercel/functions';

// Stale-while-revalidate: serves stale, revalidates in background
await invalidateByTag('blog-posts');

// Hard delete: next request blocks while fetching from origin (cache stampede risk)
await dangerouslyDeleteByTag('blog-posts', {
  revalidationDeadlineSeconds: 3600,
});

Important distinction:

cache.expireTag() — operates on Runtime Cache only
invalidateByTag() / dangerouslyDeleteByTag() — purges CDN + Runtime + Data caches

Next.js Integration

Next.js 16+ (`use cache: remote`)

// next.config.ts
const nextConfig: NextConfig = { cacheComponents: true };

import { cacheLife, cacheTag } from 'next/cache';

async function getData() {
  'use cache: remote'     // stores in Vercel Runtime Cache
  cacheTag('example-tag')
  cacheLife({ expire: 3600 })
  return fetch('https://api.example.com/data').then(r => r.json());
}

'use cache' (no : remote) — in-memory only, ephemeral per instance
'use cache: remote' — stores in Vercel Runtime Cache

Next.js 16 Invalidation APIs

Function	Context	Behavior
`updateTag(tag)`	Server Actions only	Immediate expiration, read-your-own-writes
`revalidateTag(tag, 'max')`	Server Actions + Route Handlers	Stale-while-revalidate (recommended)
`revalidateTag(tag, { expire: 0 })`	Route Handlers (webhooks)	Immediate expiration from external triggers

Important: Single-argument revalidateTag(tag) is deprecated in Next.js 16. Always pass a cacheLife profile as the second argument.

Runtime Cache vs ISR Isolation

Runtime Cache tags do NOT apply to ISR pages
cache.expireTag does NOT invalidate ISR cache
Next.js revalidatePath / revalidateTag does NOT invalidate Runtime Cache
To manage both, use same tag and purge via invalidateByTag (hits all cache layers)

CLI Cache Commands

# Purge all cached data
vercel cache purge                    # CDN + Data cache
vercel cache purge --type cdn         # CDN only
vercel cache purge --type data        # Data cache only
vercel cache purge --yes              # skip confirmation

# Invalidate by tag (stale-while-revalidate)
vercel cache invalidate --tag blog-posts,user-profiles

# Hard delete by tag (blocks until revalidated)
vercel cache dangerously-delete --tag blog-posts
vercel cache dangerously-delete --tag blog-posts --revalidation-deadline-seconds 3600

# Image invalidation
vercel cache invalidate --srcimg /images/hero.jpg

Note: --tag and --srcimg cannot be used together.

CDN Cache Tags

Add tags to CDN cached responses for later invalidation:

import { addCacheTag } from '@vercel/functions';

// Via helper
addCacheTag('product-123');

// Via response header
return Response.json(product, {
  headers: {
    'Vercel-CDN-Cache-Control': 'public, max-age=86400',
    'Vercel-Cache-Tag': 'product-123,products',
  },
});

Limits

Property	Limit
Item size	2 MB
Tags per Runtime Cache item	128
Tags per CDN item	128
Max tag length	256 bytes
Tags per bulk REST API call	16

Tags are case-sensitive and cannot contain commas.

Observability

Monitor hit rates, invalidation patterns, and storage usage in the Vercel Dashboard under Observability → Runtime Cache. The CDN dashboard (March 5, 2026) provides a unified view of global traffic distribution, cache performance metrics, a redesigned purging interface, and project-level routing — update response headers or rewrite to external APIs without triggering a new deployment. Project-level routes are available on all plans and take effect instantly.

When to Use

Caching API responses or computed data across functions in a region
Tag-based invalidation when content changes (CMS webhook → expire tag)
Reducing database load for frequently accessed data
Cross-function data sharing within a region

When NOT to Use

Framework-level page caching → use Next.js Cache Components ('use cache')
Persistent storage → use a database (Neon, Upstash)
CDN-level full response caching → use Cache-Control / Vercel-CDN-Cache-Control headers
Cross-region shared state → use a database
User-specific data that differs per request

References

📖 docs: https://vercel.com/docs/caching/runtime-cache
📖 changelog: https://vercel.com/changelog/introducing-the-runtime-cache-api
📖 CLI cache: https://vercel.com/docs/cli/cache
📖 CDN cache purging: https://vercel.com/docs/caching/cdn-cache/purge

This skill ships inside the Vercel Plugin. Listed package contents include 4 slash commands, 3 agents, hooks and an MCP server. Installed components and skill versions may vary by AI tool.

Install just this skill

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Install checklist

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npx skills add vercel/vercel-plugin --skill "runtime-cache" --full-depth

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Run this command in a terminal

npx plugins add vercel/vercel-plugin

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