Vercel Local Dev Loop

What it does

When your agent uses it

• Setting up a development environment
• Testing serverless functions locally
• Establishing a fast iteration cycle with Vercel
• With phrases like vercel dev setup

Example prompts

• “vercel dev setup”
• “vercel local development”
• “vercel dev environment”
• “/vercel-local-dev-loop”

Requirements

• Node.js
• A credential in API_SECRET
• Compatibility (from SKILL.md): Designed for Claude Code
• Pre-approved tools (allowed-tools): Read, Write, Edit, Bash(vercel:*), Bash(npm:*), Bash(npx:*), Grep

Workflow steps

6 steps, taken from the step headings in SKILL.md.

1. 1Pull Environment Variables
2. 2Start Local Dev Server
3. 3Test Serverless Functions Locally
4. 4Framework-Specific Dev Servers
5. 5Local Environment Variable Management
6. 6Testing with Vitest

What it can do on your machine

Read from SKILL.md and the folder at commit 23ea8d4. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves these tools, so the agent can use them without asking each time:

  • Read
  • Write
  • Edit
  • Bash(vercel:*)
  • Bash(npm:*)
  • Bash(npx:*)
  • Grep

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  Shell commands in SKILL.md call:

  • vercel
  • curl
  • npx
  • npm

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  Links to these hosts (documentation or services it may open):

  • vercel.com
  • vitest.dev

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names these keys or tokens, usually read from environment variables:

  • API_SECRET

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

• Compatibility

  Designed for Claude Code

  From compatibility in the SKILL.md frontmatter.

Context cost

Vercel Local Dev Loop loads about 1.5k tokens when it runs, and up to ~2.1k if it reads all its reference files. Until then it costs about 95 tokens; SKILL.md has 374 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~95

When it runs · the whole SKILL.md, loaded when a task matches

~1.5k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~2.1k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

• NoteMentions a .env fileSKILL.md:44

  # Pull env vars from Vercel to local .env files

• NoteMentions a .env fileSKILL.md:45

  vercel env pull .env.development.local

• NoteMentions a .env fileSKILL.md:47

  # This creates .env.development.local with all Development-scoped vars:

• NoteMentions a .env fileSKILL.md:76

  - Environment variables loaded from `.env*.local` files

• NoteMentions a .env fileSKILL.md:130

  vercel env pull .env.development.local

• NoteMentions a .env fileSKILL.md:168

  ## `.env` File Hierarchy

• NoteMentions a .env fileSKILL.md:174

  | `.env` | All | Commit |

• NoteMentions a .env fileSKILL.md:175

  | `.env.local` | All (local only) | Ignore |

• NoteMentions a .env fileSKILL.md:176

  | `.env.development` | Development | Commit |

• NoteMentions a .env fileSKILL.md:177

  | `.env.development.local` | Development (local only) | Ignore |

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from jeremylongshore/tons-of-skills-marketplace at commit 23ea8d4, republished under its MIT licence (© jeremylongshore). 374 words, ~1,534 tokens.

name

vercel-local-dev-loop

description

Configure Vercel local development with vercel dev, environment variables, and hot reload. Use when setting up a development environment, testing serverless functions locally, or establishing a fast iteration cycle with Vercel. Trigger with phrases like "vercel dev setup", "vercel local development", "vercel dev environment", "develop with vercel locally".

allowed-tools

Read, Write, Edit, Bash(vercel:*), Bash(npm:*), Bash(npx:*), Grep

compatibility

Designed for Claude Code

version

1.18.0

license

MIT

author

Jeremy Longshore <jeremy@intentsolutions.io>

tags

saas, vercel, development, testing, workflow

# Pull env vars from Vercel to local .env files
vercel env pull .env.development.local

# This creates .env.development.local with all Development-scoped vars:
# VERCEL="1"
# VERCEL_ENV="development"
# DATABASE_URL="postgres://..."
# API_SECRET="sk-..."

# vercel dev starts a local server that emulates the Vercel platform
vercel dev

# Output:
# Vercel CLI 39.x.x — dev command
# > Ready on http://localhost:3000

# With a specific port
vercel dev --listen 8080

# With debug logging
vercel dev --debug

# Test your API route
curl http://localhost:3000/api/hello
# {"message":"Hello from Vercel Serverless Function!"}

# Test with POST body
curl -X POST http://localhost:3000/api/users \
  -H "Content-Type: application/json" \
  -d '{"name":"test","email":"test@example.com"}'

# Test with query parameters
curl "http://localhost:3000/api/search?q=vercel&limit=10"

# Next.js — built-in Vercel compatibility
npx next dev
# API routes at pages/api/* or app/api/* work identically

# Nuxt
npx nuxi dev

# SvelteKit
npm run dev

# Astro
npx astro dev

# Add a new env var for development only
vercel env add MY_VAR development
# Prompts for value, stores encrypted on Vercel

# List all env vars
vercel env ls

# Remove an env var
vercel env rm MY_VAR development

# Pull updated vars after changes
vercel env pull .env.development.local

// api/__tests__/hello.test.ts
import { describe, it, expect, vi } from 'vitest';

// Mock the Vercel request/response
function createMockReq(overrides = {}) {
  return { method: 'GET', query: {}, body: null, ...overrides };
}

function createMockRes() {
  const res: any = {};
  res.status = vi.fn().mockReturnValue(res);
  res.json = vi.fn().mockReturnValue(res);
  res.send = vi.fn().mockReturnValue(res);
  return res;
}

describe('GET /api/hello', () => {
  it('returns 200 with message', async () => {
    const handler = (await import('../hello')).default;
    const req = createMockReq();
    const res = createMockRes();

    handler(req, res);

    expect(res.status).toHaveBeenCalledWith(200);
    expect(res.json).toHaveBeenCalledWith(
      expect.objectContaining({ message: expect.any(String) })
    );
  });
});

© jeremylongshore, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 3 other files (references) in skills/.curated/vercel-local-dev-loop of jeremylongshore/tons-of-skills-marketplace.

• SKILL.md
• references/errors.md
• references/examples.md
• references/implementation.md

Open the folder on GitHubat commit 23ea8d4