Feature requests: Server arg overrides, error details in health, and config discovery improvements

[ViperJuice]

Context

While building a skill to launch Chrome with an extension side-loaded and connect Playwright MCP via CDP, I encountered some friction points that could be improved.

Use case: Launch Chrome with --remote-debugging-port=9222 and have Playwright connect to it via --cdp-endpoint instead of launching its own browser. This enables debugging Chrome extensions with the extension already loaded.

What Worked Well

• Progressive disclosure - Only loading tool schemas on-demand is excellent for context management
• Server isolation - One server crashing (playwright-cdp) didn't affect others (filesystem, context7)
• Custom server config - Adding a custom server to ~/.pmcp.json was straightforward once discovered
• Health endpoint - Clearly shows which servers are healthy vs errored

Suggestions for Improvement

1. Server arg override/merge capability

I had to create a separate playwright-cdp entry rather than being able to add args to the manifest's playwright:

{
  "mcpServers": {
    "playwright-cdp": {
      "command": "npx",
      "args": ["-y", "@playwright/mcp@latest", "--cdp-endpoint", "http://localhost:9222"]
    }
  }
}

Suggestion: Allow overriding/extending manifest server configs:

{
  "serverOverrides": {
    "playwright": {
      "extraArgs": ["--cdp-endpoint", "http://localhost:9222"]
    }
  }
}

This would let users customize manifest servers without duplicating the entire config.

2. Error details in health endpoint

When playwright-cdp went to "error" state, the health endpoint showed:

{
  "name": "playwright-cdp",
  "status": "error",
  "tool_count": 22
}

Suggestion: Include error details:

{
  "name": "playwright-cdp",
  "status": "error",
  "tool_count": 22,
  "error": "Server process exited unexpectedly during browser_take_screenshot",
  "last_error_ts": 1234567890
}

3. CDP connection mode in manifest

For browser automation servers, the manifest could document alternative connection modes:

playwright:
  # ... existing config ...
  variants:
    cdp:
      description: "Connect to existing browser via CDP"
      extra_args: ["--cdp-endpoint", "http://localhost:9222"]
      note: "Requires browser launched with --remote-debugging-port=9222"

Or at minimum, a comment in the manifest noting this capability exists.

4. Config discovery documentation

The README mentions ~/.mcp.json for custom servers, but I initially looked in several wrong places (Claude plugin configs, etc.).

Suggestion: Add a clear "Configuration Locations" section with priority order:

Config Discovery Priority:
1. Project: .mcp.json in current directory
2. User: ~/.mcp.json or ~/.pmcp.json  
3. Custom: --config flag or PMCP_CONFIG env var

Additional Note

During testing, I discovered that browser_take_screenshot causes the Playwright MCP server to disconnect when using CDP mode. Navigation, snapshots, and clicks all work fine. This appears to be a Playwright MCP bug (not a gateway issue) - the gateway correctly isolated the failure and kept other servers running.

---

Happy to provide more details or help test any of these improvements!

[ViperJuice]

Fixed: Error details are now present in the health endpoint, manifest server arguments can be seamlessly appended via partial configs in .mcp.json, and the manifest.yaml file has been documented with the CDP workflow.