--log-file unconditionally writes all puppeteer:protocol traffic since v1.8.0 (PR #2562), ignoring DEBUG, causing log files to grow to GB scale #2731

Description of the bug

Since v1.8.0, when --log-file is set, the puppeteerLogger function in src/utils/logger.js unconditionally writes all puppeteer:protocol:SEND and puppeteer:protocol:RECV messages to the log file, regardless of the DEBUG environment variable. This is a regression introduced by #2562 ("refactor: replace debug with NodeJS native").

In v1.7.0, logger.js used the debug npm package. The saveLogsToFile() function called debug.enable() with the user's DEBUG namespaces + mcp:log, so only explicitly enabled namespaces were written to the file.

In v1.8.0+, puppeteerLogger() has a branching bug — when logFileStream is truthy (i.e. --log-file is set), it returns a write function unconditionally without checking util.debuglog(prefix).enabled or DEBUG:

// v1.8.0+ src/utils/logger.js
export const puppeteerLogger = (prefix) => {
    if (logFileStream) {
        //  ALWAYS returns a logger — DEBUG is never checked
        return (...args) => {
            logFileStream.write(`${new Date().toISOString()} ${prefix} ${util.format(...args)}\n`);
        };
    }
    // DEBUG is only checked when there is NO log file
    const dbg = util.debuglog(prefix);
    return dbg.enabled
        ? (...args) => { dbg('%s %s', new Date().toISOString(), util.format(...args)); }
        : undefined;
};

The result: every CDP wire message (network requests, responses, DOM events, accessibility tree queries, etc.) is written to disk. In real-world use, this produces gigabytes of log files, compared to kilobytes previously for the same amount of traffic.

Reproduction

Testing identical operations on v1.7.0 vs v1.9.0 with DEBUG=mcp:log (should exclude puppeteer:*):

1. Configure MCP with --log-file /path/to/log and DEBUG=mcp:log
2. Truncate the log file
3. Reload the MCP server
4. Call list_pages, then navigate_page to https://example.com, then take_snapshot
5. Count log lines by namespace

Results:

v1.7.0 correctly writes only mcp:log entries. v1.9.0 dumps 174 additional puppeteer:protocol:SEND/RECV lines containing full CDP JSON payloads (accessibility trees, network events, etc.) despite DEBUG=mcp:log.

Expectation

puppeteerLogger should respect DEBUG namespace filtering when writing to --log-file, matching v1.7.0 behavior:

• DEBUG unset → only mcp:log lines in the log file
• DEBUG=mcp:log → only mcp:log lines
• DEBUG=puppeteer:* → puppeteer lines included (opt-in)
• DEBUG=* → everything (explicit user choice)

A minimal fix would be to check util.debuglog(prefix).enabled before returning a file-writing logger:

export const puppeteerLogger = (prefix) => {
    const dbg = util.debuglog(prefix);
    if (!dbg.enabled) return undefined;
    if (logFileStream) {
        return (...args) => {
            logFileStream.write(`${new Date().toISOString()} ${prefix} ${util.format(...args)}\n`);
        };
    }
    return (...args) => {
        dbg('%s %s', new Date().toISOString(), util.format(...args));
    };
};

MCP configuration

{
  "mcpServers": {
    "chrome-devtools": {
      "command": "npx",
      "args": [
        "-y",
        "chrome-devtools-mcp@latest",
        "--log-file",
        "/path/to/chrome-devtools-mcp.log"
      ],
      "env": {
        "DEBUG": "mcp:log"
      }
    }
  }
}

Chrome DevTools MCP version

v1.8.0 and v1.9.0 affected; v1.7.0 works correctly

Chrome version

Chromium 150.0.7871.181

Coding agent version

Cursor 3.18.9

Model version

No response

Chat log

No response

Node version

v24.19.0

Operating system

Linux

Extra checklist

• I want to provide a PR to fix this bug