vercel-functions

name	vercel-functions
description	Vercel Functions expert guidance — Serverless Functions, Edge Functions, Fluid Compute, streaming, Cron Jobs, and runtime configuration. Use when configuring, debugging, or optimizing server-side code running on Vercel.
metadata	{"priority":8,"docs":["https://vercel.com/docs/functions","https://vercel.com/docs/functions/runtimes"],"sitemap":"https://vercel.com/sitemap/docs.xml","pathPatterns":["api/**/*.*","pages/api/**","src/pages/api/**","app/**/route.*","src/app/**/route.*","apps/*/api/**/*.*","apps/*/app/**/route.*","apps/*/src/app/**/route.*","apps/*/pages/api/**","vercel.json","apps/*/vercel.json"],"bashPatterns":["\\bvercel\\s+dev\\b","\\bvercel\\s+logs\\b"]}
validate	[{"pattern":"export\\s+default\\s+function","message":"Use named exports (GET, POST, PUT, DELETE) instead of default export for route handlers","severity":"error"},{"pattern":"NextApiRequest|NextApiResponse","message":"NextApiRequest/NextApiResponse are Pages Router types — use Web API Request/Response","severity":"error"},{"pattern":"from\\s+['\"](openai|@anthropic-ai/sdk|anthropic)['\"]|new\\s+(OpenAI|Anthropic)\\(","message":"Direct AI provider SDK detected in route handler. Use the Vercel AI SDK for streaming, tools, and provider abstraction.","severity":"recommended","upgradeToSkill":"ai-sdk","upgradeWhy":"Replace vendor-locked provider SDKs with @ai-sdk/openai or @ai-sdk/anthropic for unified streaming and tool support.","skipIfFileContains":"@ai-sdk/|from\\s+['\"](ai)['\"]|import.*from\\s+['\"](ai)['\"]|streamText|generateText"},{"pattern":"setTimeout\\s*\\(|setInterval\\s*\\(|await\\s+new\\s+Promise\\s*\\([^)]*setTimeout","message":"Long-running or polling logic detected in a serverless handler. Functions have execution time limits.","severity":"recommended","upgradeToSkill":"workflow","upgradeWhy":"Move delayed/polling logic to Vercel Workflow for durable execution with pause, resume, retries, and crash safety.","skipIfFileContains":"use workflow|use step|@vercel/workflow"},{"pattern":"writeFile(Sync)?\\(|createWriteStream\\(|from\\s+['\"](multer|formidable)['\"]|fs\\.writeFile","message":"Local filesystem write detected. Serverless functions have ephemeral, read-only filesystems.","severity":"error","upgradeToSkill":"vercel-storage","upgradeWhy":"Replace local filesystem writes with Vercel Blob, Neon, or Upstash for persistent, platform-native storage.","skipIfFileContains":"@vercel/blob|@upstash/|@neondatabase/"},{"pattern":"export\\s+(async\\s+)?function\\s+(GET|POST|PUT|PATCH|DELETE)\\b","message":"Route handler has no observability instrumentation. Add logging and error tracking for production debugging.","severity":"warn","upgradeToSkill":"observability","upgradeWhy":"Add structured logging, error tracking, and OTel instrumentation to route handlers.","skipIfFileContains":"console\\.error|logger\\.|captureException|Sentry|@vercel/otel|withTracing"},{"pattern":"from\\s+['\"\"](lru-cache|node-cache|memory-cache)['\"\"]|new\\s+(LRUCache|NodeCache|Map)\\(\\s*\\).*cache","message":"In-process memory cache detected in serverless function. Process memory is not shared across invocations.","severity":"recommended","upgradeToSkill":"runtime-cache","upgradeWhy":"Replace in-process caches with Vercel Runtime Cache (getCache from @vercel/functions) for region-aware caching that persists across invocations.","skipIfFileContains":"getCache|from\\s+['\"\"]\\@vercel/functions['\"\"]"},{"pattern":"maxRetries\\s*[=:]|retryCount\\s*[=:]|retry\\s*\\(\\s*|for\\s*\\([^)]*retry|while\\s*\\([^)]*retry","message":"Manual retry logic detected. Use Vercel Workflow DevKit for automatic retries with durable execution.","severity":"recommended","upgradeToSkill":"workflow","upgradeWhy":"Replace manual retry loops with Workflow DevKit steps that provide automatic retries, crash safety, and observability.","skipIfFileContains":"use workflow|use step|@vercel/workflow|from\\s+['\"\"](workflow)['\"\"]"},{"pattern":"from\\s+['\"](express)['\"\"]|require\\s*\\(\\s*['\"](express)['\"\"\\)]","message":"Express.js detected in a Vercel project. Vercel Functions use the Web Request/Response API — Express middleware, req/res, and app.listen() do not work in serverless.","severity":"recommended","upgradeToSkill":"vercel-functions","upgradeWhy":"Replace Express with Next.js route handlers (export async function GET/POST) or Vercel Functions using the Web Request/Response API.","skipIfFileContains":"export\\s+(async\\s+)?function\\s+(GET|POST|PUT|PATCH|DELETE)|from\\s+['\"\"](next/server|@vercel/functions)['\"\"]"}]
retrieval	{"aliases":["serverless functions","api routes","edge functions","lambda"],"intents":["create serverless function","configure function runtime","optimize cold starts","add api route"],"entities":["Serverless Functions","Edge Functions","Fluid Compute","streaming","Cron Jobs"]}
chainTo	[{"pattern":"from\\s+['\\\"](openai|@anthropic-ai/sdk|anthropic)['\"]|new\\s+(OpenAI|Anthropic)\\(","targetSkill":"ai-sdk","message":"Direct AI provider SDK in route handler — loading AI SDK guidance for unified streaming and tool support."},{"pattern":"setTimeout\\s*\\(|setInterval\\s*\\(|await\\s+new\\s+Promise\\s*\\([^)]*setTimeout","targetSkill":"workflow","message":"Long-running or polling logic in serverless handler — loading Workflow DevKit for durable execution."},{"pattern":"writeFile(Sync)?\\(|createWriteStream\\(|from\\s+['\\\"](multer|formidable)['\"]|fs\\.writeFile","targetSkill":"vercel-storage","message":"Local filesystem write in serverless function — loading Vercel Storage guidance for platform-native persistence."},{"pattern":"from\\s+['\"\"]@vercel/(postgres|kv)['\"\"]","targetSkill":"vercel-storage","message":"@vercel/postgres and @vercel/kv are sunset — loading Vercel Storage guidance for Neon and Upstash migration."},{"pattern":"generateObject\\s*\\(|streamObject\\s*\\(|toDataStreamResponse|maxSteps\\b|CoreMessage\\b","targetSkill":"ai-sdk","message":"Deprecated AI SDK v5 API detected — loading AI SDK v6 guidance for migration."},{"pattern":"while\\s*\\(\\s*true\\s*\\)\\s*\\{|for\\s*\\(\\s*;\\s*;\\s*\\)\\s*\\{|setInterval\\s*\\(\\s*async","targetSkill":"workflow","message":"Polling loop in serverless function detected — loading Workflow DevKit for durable, crash-safe execution with pause/resume.","skipIfFileContains":"use workflow|use step|from\\s+['\"]workflow['\"]"},{"pattern":"from\\s+['\"]express['\"]|require\\s*\\(\\s*['\"]express['\"]","targetSkill":"vercel-functions","message":"Express.js detected — loading Vercel Functions guidance for Web Request/Response API route handlers that replace Express middleware and routing.","skipIfFileContains":"export\\s+(async\\s+)?function\\s+(GET|POST|PUT|PATCH|DELETE)"},{"pattern":"from\\s+['\"\"](lru-cache|node-cache|memory-cache)['\"\"]|new\\s+(LRUCache|NodeCache|Map)\\(\\s*\\).*cache","targetSkill":"runtime-cache","message":"In-process memory cache in serverless function — loading Runtime Cache guidance for region-aware caching that persists across invocations.","skipIfFileContains":"getCache|from\\s+['\"\"]\\@vercel/functions['\"\"]"},{"pattern":"maxRetries\\s*[=:]|retryCount\\s*[=:]|retry\\s*\\(\\s*|for\\s*\\([^)]*retry|while\\s*\\([^)]*retry","targetSkill":"workflow","message":"Manual retry logic in serverless handler — loading Workflow DevKit guidance for automatic retries with durable execution.","skipIfFileContains":"use workflow|use step|@vercel/workflow|from\\s+['\"\"](workflow)['\"\"]"}]

Vercel Functions

You are an expert in Vercel Functions — the compute layer of the Vercel platform.

Function Types

Serverless Functions (Node.js)

• Full Node.js runtime, all npm packages available
• Default for Next.js API routes, Server Actions, Server Components
• Cold starts: 800ms–2.5s (with DB connections)
• Max duration: 10s (Hobby), 300s (Pro default), 800s (Fluid Compute Pro/Enterprise)

// app/api/hello/route.ts
export async function GET() {
  return Response.json({ message: 'Hello from Node.js' })
}

Edge Functions (V8 Isolates)

• Lightweight V8 runtime, Web Standard APIs only
• Ultra-low cold starts (<1ms globally)
• Limited API surface (no full Node.js)
• Best for: auth checks, redirects, A/B testing, simple transformations

// app/api/hello/route.ts
export const runtime = 'edge'

export async function GET() {
  return new Response('Hello from the Edge')
}

Bun Runtime (Public Beta)

Add "bunVersion": "1.x" to vercel.json to run Node.js functions on Bun instead. ~28% lower latency for CPU-bound workloads. Supports Next.js, Express, Hono, Nitro.

Rust Runtime (Public Beta)

Rust functions run on Fluid Compute with HTTP streaming and Active CPU pricing. Built on the community Rust runtime. Supports environment variables up to 64 KB.

Node.js 24 LTS

Node.js 24 LTS is now GA on Vercel for both builds and functions. Features V8 13.6, global URLPattern, Undici v7 for faster fetch(), and npm v11.