Tests and the dev-server MCP

What runs where

Runner	Covers	Why that runner
Vitest 5	Season window, rate limiter, Zod schema, hostname check	Pure functions; milliseconds
Playwright 1.64	Proxy rewrite, both themes, 404s, canonical links, npm versions, the full contact form	Only a real server exercises proxy + prerender + Server Action together

"scripts": {
  "lint": "eslint .",
  "typecheck": "next typegen && tsc --noEmit",
  "test": "vitest run",
  "test:e2e": "playwright test",
  "verify": "npm run lint && npm run typecheck && npm run test && npm run build"
}

next lint is gone in 16 — use the ESLint CLI.

Playwright against a production build

webServer: {
  command: `${process.env.E2E_SKIP_BUILD ? "" : "npm run build && "}npx next start -p 3100`,
  url: "http://localhost:3100/standard",
  env: { CONTACT_DRY_RUN: "1" },   // log emails instead of sending
},

The form test fills the form, waits for the Turnstile test widget to set its token, submits, and expects the success message.

The dev-server MCP endpoint

next dev in Next.js 16 serves an MCP endpoint at /_next/mcp. You don’t need a client for it — it speaks JSON-RPC over HTTP:

curl -s -X POST http://localhost:3000/_next/mcp \
  -H 'content-type: application/json' \
  -H 'accept: application/json, text/event-stream' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"get_errors","arguments":{}}}'

Useful tools: get_project_metadata, get_routes, get_compilation_issues (compiles every route without a browser), get_errors (needs the page open in a browser), get_page_metadata (which layout, page and boundaries rendered), and get_logs (path to the dev log — where the dry-run emails appear).