Dev Server Agent Skill

Dev Server Skill

Use this skill to start the Cosmos Explorer webpack dev server and connect to it with the Playwright MCP browser for interactive testing, debugging, or previewing the application.

Pre-Start: Check Dependencies

Before starting the dev server, check whether npm install needs to be run:

if [ ! -d node_modules ] || [ package.json -nt node_modules ] || [ package-lock.json -nt node_modules ]; then
  npm install
fi

On Windows PowerShell:

if (-not (Test-Path node_modules) -or
    (Get-Item package.json).LastWriteTime -gt (Get-Item node_modules).LastWriteTime -or
    (Get-Item package-lock.json).LastWriteTime -gt (Get-Item node_modules).LastWriteTime) {
    npm install
}

Always run this check before starting the dev server.

Check for Existing Server

Before starting a new server, check if one is already running on port 1234:

try {
    $response = Invoke-WebRequest -Uri "https://localhost:1234/_ready" -SkipCertificateCheck -UseBasicParsing -ErrorAction Stop
    if ($response.StatusCode -eq 200) {
        Write-Host "Dev server is already running and ready!"
    }
} catch {
    Write-Host "No dev server detected, starting a new one..."
}

If the server is already running and ready, skip to Connect the Playwright Browser.

Start the Dev Server

Start the webpack dev server as a detached background process so it persists across session changes:

npm start

The dev server:

• Runs at https://localhost:1234 (HTTPS with self-signed certificate)
• Uses webpack dev mode with live reload
• Exposes a /_ready health-check endpoint

Wait for Compilation

After starting the server, poll the /_ready endpoint until it returns HTTP 200. Do not proceed to browser navigation until /_ready returns 200.

On Windows PowerShell:

$timeout = 120
$elapsed = 0
while ($elapsed -lt $timeout) {
    try {
        $response = Invoke-WebRequest -Uri "https://localhost:1234/_ready" -SkipCertificateCheck -UseBasicParsing -ErrorAction Stop
        if ($response.StatusCode -eq 200) {
            Write-Host "Dev server is ready!"
            break
        }
    } catch {
        # Server not ready yet
    }
    Start-Sleep -Seconds 3
    $elapsed += 3
}
if ($elapsed -ge $timeout) {
    Write-Error "Dev server did not become ready within $timeout seconds"
}

On bash:

timeout=120
elapsed=0
while [ $elapsed -lt $timeout ]; do
  if curl -sk https://localhost:1234/_ready 2>/dev/null | grep -q "Compilation complete"; then
    echo "Dev server is ready!"
    break
  fi
  sleep 3
  elapsed=$((elapsed + 3))
done
if [ $elapsed -ge $timeout ]; then
  echo "Dev server did not become ready within $timeout seconds" >&2
fi

Connect the Playwright Browser

Once the dev server is ready, use the Playwright MCP browser tools to navigate to the application.

Navigate to the desired entry point:

• https://localhost:1234/hostedExplorer.html — Hosted explorer (standalone mode). Best for general UI testing and interaction without Azure Portal framing.
• https://localhost:1234/explorer.html — Portal explorer (Azure Portal iframe mode). Requires portal context/messages to initialize fully.
• https://localhost:1234/index.html — Emulator mode. Requires a local Cosmos DB Emulator running on port 8081.
• https://localhost:1234/testExplorer.html — Test explorer (dev mode only). Used for E2E test harness.

Default Navigation

When no specific page is requested, navigate to https://localhost:1234/hostedExplorer.html as it provides the most complete standalone experience.

Dismiss Webpack Warnings Overlay

After the page loads, a webpack dev server overlay may appear inside an iframe showing DefinePlugin warnings. If a "Dismiss" button (×) is visible in the overlay, click it to close the warnings before proceeding with any other interaction.

Available Pages Reference

| URL | Entry Point | Description |

|-----|-------------|-------------|

| /hostedExplorer.html | src/HostedExplorer.tsx | Standalone hosted explorer (cosmos.azure.com) |

| /explorer.html | src/Main.tsx | Portal iframe explorer |

| /index.html | src/Index.tsx | Emulator explorer |

| /testExplorer.html | test/testExplorer/TestExplorer.ts | Test harness (dev mode only) |

| /terminal.html | src/Terminal/index.ts | Notebook terminal |

| /quickstart.html | src/quickstart.ts | Quickstart page |

| /selfServe.html | src/SelfServe/SelfServe.tsx | Self-serve configuration |

| /galleryViewer.html | src/GalleryViewer/GalleryViewer.tsx | Notebook gallery viewer |

Troubleshooting

HTTPS / Self-Signed Certificate Errors

The dev server uses HTTPS with a self-signed certificate. If the Playwright browser fails to navigate with an error like ERR_CERT_AUTHORITY_INVALID or any other SSL/TLS certificate error, stop immediately and tell the user:

> The Playwright MCP server needs the --ignore-https-errors argument to connect to the dev server's self-signed certificate. Please add --ignore-https-errors to your Playwright MCP server configuration and try again.

Do not attempt workarounds (e.g., creating new browser contexts manually). The --ignore-https-errors flag is the correct fix.

Guidelines

• Always start the dev server as a detached background process so it survives session changes.
• Always wait for /_ready to return 200 before navigating the browser.
• Ignore certificate errors in shell HTTP requests (e.g., -SkipCertificateCheck, curl -k). For the Playwright browser, the --ignore-https-errors MCP argument must be configured.
• If the dev server is already running on port 1234, reuse it instead of starting a new one.
• If the server fails to start, check for port conflicts (netstat -ano | findstr :1234 on Windows).
• When stopping the dev server, use Stop-Process with the specific PID of the node process.