lighthouse_audit always fails: Network.emulateNetworkConditions timed out (even with increased protocolTimeout)

[CressZZ]

Description of the bug

Description

lighthouse_audit tool always fails with Network.emulateNetworkConditions timed out error, regardless of mode
(navigation/snapshot) or device (mobile/desktop).

Other tools like performance_start_trace, navigate_page, list_pages work perfectly fine on the same Chrome instance.

Environment

• chrome-devtools-mcp version: 0.21.0 (latest, installed via npx chrome-devtools-mcp@latest)
• Chrome version: 146.0.7680.165
• OS: macOS (Darwin 25.3.0)

Steps to Reproduce

1. Start chrome-devtools-mcp (v0.21.0)
2. Navigate to any page (e.g., https://web.dev)
3. Call lighthouse_audit with any combination of parameters — all fail

Error

Network.emulateNetworkConditions timed out. Increase the 'protocolTimeout' setting in launch/connect calls for a higher timeout if needed.

Investigation

It's NOT a timeout issue

The Lighthouse bundle (lighthouse-devtools-mcp-bundle.js:57060) has:

var DEFAULT_PROTOCOL_TIMEOUT = 3e4; // 30 seconds

Manually patched to 18e4 (180s), restarted MCP — still fails. Chrome never responds to the command.

Other CDP commands work fine

• performance_start_trace → works
• navigate_page → works
• Lighthouse CLI (npx lighthouse) on the same machine → works

Root Cause Hypothesis

Lighthouse's internal CDP session sends Network.emulateNetworkConditions but Chrome never responds. Possibly:

1. CDP session conflict — MCP's existing session holds the Network domain, blocking Lighthouse's session
2. Pipe-based connection issue — Lighthouse may not handle --remote-debugging-pipe transport correctly

Related

• protocolTimeout is too short #323 (protocolTimeout increase in v0.7.0)
• Timeout issues when getting performance metrics #124 (timeout issues with performance metrics)

Reproduction

No response

Expectation

No response

MCP configuration

No response

Chrome DevTools MCP version

0.21.0

Chrome version

No response

Coding agent version

No response

Model version

No response

Chat log

No response

Node version

No response

Operating system

None

Extra checklist

• I want to provide a PR to fix this bug

[OrKoN]

Reported previously here #1248 (comment) This was not reproducible for me. Can you record a screencast of this happening from the start of the MCP session?