DDEV Add-on for MCP Server Testing with Playwright

I built a DDEV add-on that runs Playwright checks against local MCP endpoints using internal DDEV DNS names like web. This solves flaky localhost-based testing and gives one command for repeatable MCP smoke tests.

The Problem

Teams testing MCP servers locally usually mix host networking, ad-hoc scripts, and one-off commands. That breaks quickly when ports change or when tests run from a different container context.

Pain point	Typical failure
Host-only URLs (localhost)	Fails inside containers where service DNS is required
Manual Playwright setup per project	Inconsistent versions and missing browser deps
No MCP-specific smoke command	Health-check regressions are discovered too late

Related context: Build: MCP Web Setup, Build: Drupal MCP Toolkit, Drupal Context MCP Integration.

The Solution

The add-on installs:

• A dedicated mcp-playwright service via Docker Compose.
• DDEV commands: ddev mcp-pw-smoke and ddev mcp-pw-test.
• A Playwright smoke test for GET /health with configurable MCP_BASE_URL.

Tech Stack

Component	Technology	Why
Container platform	DDEV / Docker Compose	Standard local dev for CMS projects
Test runner	Playwright v1.56.1	Reliable browser automation with built-in assertions
Base image	mcr.microsoft.com/playwright:v1.56.1-noble	All browser deps pre-installed
Service DNS	DDEV internal networking	web resolves to the app container without port hacks

Implementation

Docker Compose

.ddev/docker-compose.mcp-playwright.yaml

services:
  mcp-playwright:
image: mcr.microsoft.com/playwright:v1.56.1-noble
working_dir: /var/www/html/.ddev/mcp-playwright

DDEV Command

.ddev/commands/host/mcp-pw-smoke

ddev exec -s mcp-playwright "cd /var/www/html/.ddev/mcp-playwright && npm ci --silent && MCP_BASE_URL=${MCP_BASE_URL:-http://web:3100} npx playwright test tests/mcp-health.spec.js --reporter=line"

Smoke Test

.ddev/mcp-playwright/tests/mcp-health.spec.js

const response = await request.get(`${baseUrl}/health`);
expect(response.ok()).toBeTruthy();

Use DDEV DNS Names, Not localhost

web DNS names inside DDEV are safer than localhost for cross-container test reliability. When your test runner lives in a sidecar container, localhost points to the sidecar itself, not your app.

URL Format Bugs Are Silent

A tiny helper (resolveMcpBaseUrl) plus tests prevents subtle URL-format bugs. Trailing slashes, missing ports, and protocol mismatches fail silently and waste hours of debugging.

Full add-on file structure

.ddev/
  docker-compose.mcp-playwright.yaml
  commands/
    host/
      mcp-pw-smoke
      mcp-pw-test
  mcp-playwright/
    package.json
    playwright.config.js
    tests/
      mcp-health.spec.js

Why this matters for Drupal and WordPress

DDEV is the standard local development environment for Drupal projects and increasingly adopted by WordPress teams. Any Drupal or WordPress site integrating MCP-based AI tools -- content analyzers, module generators, migration assistants -- needs reliable endpoint testing before deployment. This add-on gives CMS teams a single command to verify MCP server health inside the same container stack they already use for local development, eliminating the gap between "it works on my machine" and CI-reproducible smoke tests.

What I Learned

• web DNS names inside DDEV are safer than localhost for cross-container test reliability.
• A tiny helper (resolveMcpBaseUrl) plus tests prevents subtle URL-format bugs.
• Dedicated smoke commands are worth adding early when MCP endpoints are a release gate.

References

• View Code
• https://ddev.readthedocs.io/en/stable/users/extend/additional-services/
• https://playwright.dev/docs/test-intro

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Looking for an Architect who doesn't just write code, but builds the AI systems that multiply your team's output? View my enterprise CMS case studies at victorjimenezdev.github.io or connect with me on LinkedIn.