vercel-load-scale

name	vercel-load-scale
description	Load test and scale Vercel deployments with concurrency tuning and capacity planning. Use when running performance tests, planning for traffic spikes, or optimizing serverless function scaling on Vercel. Trigger with phrases like "vercel load test", "vercel scale", "vercel performance test", "vercel capacity", "vercel benchmark".
allowed-tools	Read, Write, Edit, Bash(npx:*), Bash(vercel:*), Bash(curl:*)
version	1.18.0
license	MIT
author	Jeremy Longshore <[e-mail]>
tags	["saas","vercel","testing","performance","scaling"]
compatibility	Designed for Claude Code

Vercel Load & Scale

Overview

Load test Vercel deployments to identify scaling limits, cold start impact, and concurrency thresholds. Covers k6/autocannon test scripts, Vercel's auto-scaling model, Fluid Compute concurrency, and capacity planning.

Prerequisites

• Load testing tool: k6, autocannon, or artillery
• Test environment deployment (never load test production without approval)
• Access to Vercel Analytics for monitoring during tests

Instructions

Step 1: Understand Vercel's Scaling Model

Vercel serverless functions scale automatically:

Behavior	Details
Scale-up	New function instances spawn on demand
Scale-down	Idle instances shut down after ~15 minutes
Cold starts	First request to a new instance pays initialization cost
Concurrency	Each instance handles one request at a time (by default)
Fluid Compute	Pro/Enterprise: multiple requests per instance

Concurrency limits by plan:

Plan	Max Concurrent Functions
Hobby	10
Pro	1,000
Enterprise	100,000

Step 2: Basic Load Test with autocannon

# Install autocannon
npm install -g autocannon

# Test with 50 concurrent connections for 30 seconds
autocannon -c 50 -d 30 https://my-app-preview.vercel.app/api/endpoint

# Output includes:
# Latency: avg, p50, p99, max
# Requests/sec: avg, min, max
# Errors: timeouts, non-2xx responses

Step 3: k6 Load Test Script

// load-test.js
import http from 'k6/http';
import { check, sleep } from 'k6';
 { ,  }  ;

 errorRate =  ();
 coldStartRate =  ();
 latency =  ();

  options = {
  : [
    { : , :  },   
    { : , :  },   
    { : , :  },  
    { : , :  },    
  ],
  : {
    : [],  
    : [],              
  },
};

   () {
   res = http.();

  (res, {
    :  r. === ,
    :  r.. < ,
  });

  errorRate.(res. !== );
  latency.(res..);

  
   (res.[] === ) {
    coldStartRate.();
  }

  ();
}