## Problem `--blockedUrlPattern`/`--allowedUrlPattern` accept any URLPattern string, including hostnames that use a regexp group (for example `*://(127\.\d+\.\d+\.\d+):*/*`, meant to cover a whole IP range). That pattern is enforced correctly by the target-attach check (`TargetManager#isUrlAllowed`, using the real `URLPattern.test()`), but the actual network-level blocking runs through the CDP command `Network.emulateNetworkConditionsByRule`, passing the raw pattern string as `NetworkConditions.urlPattern`. That command's native matching does not apply the pattern consistently on redirects, so a page allowed to load can redirect straight through a blocked host range while an exact-hostname pattern stays blocked in both cases. Root-caused and written up in more detail on #2777. This isn't something fixable from this repo's side (the mismatch is between the documented CDP `urlPattern` semantics and the underlying Chromium implementation for `emulateNetworkConditionsByRule`, not in `puppeteer-core` or `chrome-devtools-mcp`), so instead of leaving the gap silent, this rejects patterns this repo can't currently guarantee are enforced. ## Fix - Added `findUnenforceableHostnamePattern` (`src/utils/url.ts`), which parses each pattern with `URLPattern` and flags one whose canonicalized `hostname` contains a regexp group (`(`). Wildcard (`*`) and named-group (`:name`) hostnames are unaffected and continue to work as before; a regexp group outside the hostname (e.g. in the pathname) is also left alone, since only the hostname case is demonstrated as broken. - Wired it into the `blockedUrlPattern`/`allowedUrlPattern` CLI option `coerce`, so an offending pattern fails fast at startup with a clear error instead of silently only half-working. - Updated both options' `describe` text and regenerated `docs/configuration.md` via `npm run gen`. ## Testing - Added unit tests in `tests/utils/url.test.ts` covering: a hostname regexp group (flagged), multiple patterns (first offender returned), an exact hostname, a wildcard hostname, a named-group hostname, a regexp group outside the hostname, and a pattern that fails to construct. - `npx tsc` and `npx eslint` both pass clean on the changed files. - Verified the new function's behavior against Puppeteer's own vendored `URLPattern` polyfill (`node_modules/puppeteer-core/lib/third_party/urlpattern-polyfill`), matching every case in the new test suite - my local Node (22.22) predates Node's global `URLPattern` support that this repo's `.nvmrc` (v24) assumes, so I couldn't run the built test file directly against the global here, but the polyfill is the same spec implementation and gave identical results for all cases. Fixes #2777 --------- Co-authored-by: Natasha Gorshunova <47688881+nattallius@users.noreply.github.com>
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Configuration
The Chrome DevTools MCP server supports the following configuration option:
-
--categoryInput/--category-inputSet to false to exclude tools related to input.- Type: boolean
- Default:
true
-
--categoryNavigation/--category-navigationSet to false to exclude tools related to navigation.- Type: boolean
- Default:
true
-
--categoryEmulation/--category-emulationSet to false to exclude tools related to emulation.- Type: boolean
- Default:
true
-
--categoryPerformance/--category-performanceSet to false to exclude tools related to performance.- Type: boolean
- Default:
true
-
--categoryNetwork/--category-networkSet to false to exclude tools related to network.- Type: boolean
- Default:
true
-
--categoryDebugging/--category-debuggingSet to false to exclude tools related to debugging.- Type: boolean
- Default:
true
-
--categoryExtensions/--category-extensionsSet to true to include tools related to extensions. Note: This feature is currently only supported with a pipe connection. autoConnect, browserUrl, and wsEndpoint are not supported with this feature until 149 will be released.- Type: boolean
- Default:
false
-
--categoryExperimentalThirdParty/--category-experimental-third-partySet to true to enable third-party developer tools exposed by the inspected page itself- Type: boolean
- Default:
false
-
--categoryMemory/--category-memorySet to false to exclude tools related to memory.- Type: boolean
- Default:
true
-
--categoryExperimentalWebmcp/--category-experimental-webmcpSet to true to enable debugging WebMCP tools. Requires Chrome 150+ with the following flag:--enable-features=WebMCP- Type: boolean
- Default:
false
-
--categoryPwa/--category-pwaSet to true to include tools for automating Progressive Web Apps (install, launch, uninstall, and OS state). This feature is only supported with a pipe connection; autoConnect, browserUrl, and wsEndpoint are not supported.- Type: boolean
- Default:
false
-
--autoConnect/--auto-connectIf specified, automatically connects to a browser (Chrome 144+) running locally from the user data directory identified by the channel param (default channel is stable). Requires the remote debugging server to be started in the Chrome instance via chrome://inspect/#remote-debugging.- Type: boolean
- Default:
false
-
--browserUrl/--browser-url,-uConnect to a running, debuggable Chrome instance (e.g.http://127.0.0.1:9222). For more details see: https://github.com/ChromeDevTools/chrome-devtools-mcp/blob/main/docs/advanced-usage.md#connecting-to-a-running-chrome-instance.- Type: string
-
--wsEndpoint/--ws-endpoint,-wWebSocket endpoint to connect to a running Chrome instance (e.g., ws://127.0.0.1:9222/devtools/browser/). Alternative to --browserUrl.- Type: string
-
--wsHeaders/--ws-headersCustom headers for WebSocket connection in JSON format (e.g., '{"Authorization":"Bearer token"}'). Only works with --wsEndpoint.- Type: string
-
--headlessWhether to run in headless (no UI) mode.- Type: boolean
- Default:
false
-
--executablePath/--executable-path,-ePath to custom Chrome executable.- Type: string
-
--isolatedIf specified, creates a temporary user-data-dir that is automatically cleaned up after the browser is closed. Defaults to false.- Type: boolean
- Default:
false
-
--userDataDir/--user-data-dirPath to the user data directory for Chrome. Default is $HOME/.cache/chrome-devtools-mcp/chrome-profile$CHANNEL_SUFFIX_IF_NON_STABLE- Type: string
-
--channelSpecify a different Chrome channel that should be used. The default is the stable channel version.- Type: string
- Choices:
canary,dev,beta,stable
-
--proxyServer/--proxy-serverProxy server configuration for Chrome passed as --proxy-server when launching the browser. See https://www.chromium.org/developers/design-documents/network-settings/ for details.- Type: string
-
--chromeArg/--chrome-argAdditional arguments for Chrome. Only applies when Chrome is launched by chrome-devtools-mcp.- Type: array
-
--ignoreDefaultChromeArg/--ignore-default-chrome-argExplicitly disable default arguments for Chrome. Only applies when Chrome is launched by chrome-devtools-mcp.- Type: array
-
--logFile/--log-filePath to a file to write debug logs to. Set the env variableNODE_DEBUGto*to enable verbose logs. Useful for submitting bug reports.- Type: string
-
--viewportInitial viewport size for the Chrome instances started by the server. For example,1280x720. In headless mode, max size is 3840x2160px.- Type: string
-
--acceptInsecureCerts/--accept-insecure-certsIf enabled, ignores errors relative to self-signed and expired certificates. Use with caution.- Type: boolean
- Default:
false
-
--pageIdRouting/--page-id-routingRequire pageId on page-scoped tools and route requests by page ID (useful for concurrent agent sessions). Use --no-page-id-routing to disable.- Type: boolean
- Default:
true
-
--experimentalDevtools/--experimental-devtoolsWhether to enable automation over DevTools targets- Type: boolean
- Default:
false
-
--experimentalVision/--experimental-visionWhether to enable coordinate-based tools such as click_at(x,y). Usually requires a computer-use model able to produce accurate coordinates by looking at screenshots.- Type: boolean
- Default:
false
-
--memoryDebugging/--memory-debugging,--experimentalMemoryWhether to enable memory debugging tools.- Type: boolean
- Default:
false
-
--experimentalStructuredContent/--experimental-structured-contentWhether to output structured formatted content.- Type: boolean
- Default:
false
-
--experimentalIncludeAllPages/--experimental-include-all-pagesWhether to include all kinds of pages such as webviews or background pages as pages.- Type: boolean
- Default:
false
-
--experimentalScreencast/--experimental-screencastExposes experimental screencast tools (requires ffmpeg). Install ffmpeg https://www.ffmpeg.org/download.html and ensure it is available in the MCP server PATH.- Type: boolean
- Default:
false
-
--experimentalFfmpegPath/--experimental-ffmpeg-pathPath to ffmpeg executable for screencast recording.- Type: string
-
--experimentalScreencastFps/--experimental-screencast-fpsFrames per second to use for screencast recording. Lower values can reduce memory pressure on pages that produce frames faster than ffmpeg can encode them.- Type: number
-
--blockedUrlPattern/--blocked-url-patternRestricts browser's network access by blocking specified URL patterns (uses https://urlpattern.spec.whatwg.org/). Silently detaches from targets with blocked URLs upon connection, and blocks runtime requests (including navigations and subresources). Accepts an array of patterns. A pattern that uses a regexp group in any component (for example(127\.\d+\.\d+\.\d+)in the hostname) is rejected, because it is not enforced on redirects or subresources; use an exact value or a*/:namewildcard instead.- Type: array
-
--allowedUrlPattern/--allowed-url-patternRestricts browser's network access by allowing only specified URL patterns (uses https://urlpattern.spec.whatwg.org/). Requires Chrome 149+. Silently detaches from targets with unallowed URLs upon connection, and blocks runtime requests (including navigations and subresources). Accepts an array of patterns. A pattern that uses a regexp group in any component (for example(127\.\d+\.\d+\.\d+)in the hostname) is rejected, because it is not enforced on redirects or subresources; use an exact value or a*/:namewildcard instead.- Type: array
-
--performanceCrux/--performance-cruxSet to false to disable sending URLs from performance traces to CrUX API to get field performance data.- Type: boolean
- Default:
true
-
--usageStatistics/--usage-statisticsSet to false to opt-out of usage statistics collection. Google collects usage data to improve the tool, handled under the Google Privacy Policy (https://policies.google.com/privacy). This is independent from Chrome browser metrics. Disabled ifCHROME_DEVTOOLS_MCP_NO_USAGE_STATISTICSorCIenv variables are set.- Type: boolean
- Default:
true
-
--javascriptEvaluation/--javascript-evaluationSet to false to disable JavaScript execution. When disabled, evaluation tools (evaluate_script and slim evaluate) are disabled, the initScript parameter in navigate_page is turned off, and navigating to javascript:, data:, or vbscript: URLs is disallowed.- Type: boolean
- Default:
true
-
--sourceMaps/--source-mapsWhether to enable source maps in DevTools. Use --no-source-maps to disable.- Type: boolean
- Default:
true
-
--screenshotFormat/--screenshot-formatOverride the default output format used by take_screenshot when the caller does not specify one. JPEG and WebP are ~3-5x smaller than PNG, which reduces transfer and storage size. To reduce context size use --screenshotMaxWidth / --screenshotMaxHeight, since image tokens scale with dimensions rather than encoded bytes. Unset preserves the existing default ("png").- Type: string
- Choices:
jpeg,png,webp
-
--screenshotQuality/--screenshot-qualityOverride the default compression quality (0-100) used by take_screenshot for JPEG and WebP when the caller does not specify one. Lower values mean smaller files. Ignored for PNG. Unset preserves the Puppeteer default.- Type: number
-
--screenshotMaxWidth/--screenshot-max-widthMaximum width in pixels for screenshots. If the captured image is wider, it is downscaled (preserving aspect ratio) before being returned. Reduces context size in AI conversations. Unset means no resize.- Type: number
-
--screenshotMaxHeight/--screenshot-max-heightMaximum height in pixels for screenshots. If the captured image is taller, it is downscaled (preserving aspect ratio) before being returned. Can be combined with --screenshot-max-width; the smaller scale factor wins. Unset means no resize.- Type: number
-
--slimExposes a "slim" set of 3 tools covering navigation, script execution and screenshots only. Useful for basic browser tasks.- Type: boolean
- Default:
false
-
--redactNetworkHeaders/--redact-network-headersIf true, redacts some of the network headers considered sensitive before returning to the client.- Type: boolean
- Default:
false
-
--allowUnrestrictedPaths/--allow-unrestricted-pathsIf set, disables the default path restriction that applies when the MCP client does not negotiate the roots capability. By default, file-writing tools are restricted to the OS temp directory when no roots are configured. Use this only when connecting a trusted local client that does not implement MCP roots and requires access to paths outside the temp directory.- Type: boolean
- Default:
false
-
--filesystemRoot/--filesystem-root,--workspaceA directory that filesystem tools are allowed to access. May be specified more than once.- Type: array
- Default:
OS temp directory
-
--configPath to JSON configuration file.- Type: string
Pass them via the args property in the JSON configuration. For example:
{
"mcpServers": {
"chrome-devtools": {
"command": "npx",
"args": [
"chrome-devtools-mcp@latest",
"--channel=canary",
"--headless=true",
"--isolated=true"
]
}
}
}
Connecting via WebSocket with custom headers
You can connect directly to a Chrome WebSocket endpoint and include custom headers (e.g., for authentication):
{
"mcpServers": {
"chrome-devtools": {
"command": "npx",
"args": [
"chrome-devtools-mcp@latest",
"--wsEndpoint=ws://127.0.0.1:9222/devtools/browser/<id>",
"--wsHeaders={\"Authorization\":\"Bearer YOUR_TOKEN\"}"
]
}
}
}
To get the WebSocket endpoint from a running Chrome instance, visit http://127.0.0.1:9222/json/version and look for the webSocketDebuggerUrl field.
You can also run npx chrome-devtools-mcp@latest --help to see all available configuration options.