Prebid Chrome Devtools

Prebid Chrome DevTools

Inspect Prebid's runtime through its page-provided summary, auctions, and events tools. Treat the integration as experimental and confirm discovery instead of assuming that it is active.

Install Chrome DevTools MCP

First check for the specific list_3p_developer_tools and execute_3p_developer_tool tools. Generic Chrome DevTools MCP tools are not enough: an existing server started with its default arguments omits these two third-party tools.

• If both third-party tools are present, keep the existing server and continue to Prepare Prebid.js.
• If generic Chrome DevTools MCP tools are present but the third-party tools are absent, reconfigure the existing server to append --categoryExperimentalThirdParty=true, preserving any browser connection or other custom arguments. Restart the MCP client because a running server's startup arguments cannot be changed. Do not register a duplicate server.
• If no Chrome DevTools MCP tools are present, install the server as described below.

When Codex CLI is available and the server is absent, run:

codex mcp add chrome-devtools -- npx -y chrome-devtools-mcp@latest --categoryExperimentalThirdParty=true

For an existing Codex registration, inspect it with codex mcp get chrome-devtools. Update the corresponding MCP configuration so its args retain the existing values and include --categoryExperimentalThirdParty=true; then restart Codex. If the CLI or client cannot edit a registration in place, remove and re-add it only after recording and restoring all of its existing arguments and environment settings.

For another MCP client, add the equivalent server configuration:

{
  "mcpServers": {
    "chrome-devtools": {
      "command": "npx",
      "args": [
        "-y",
        "chrome-devtools-mcp@latest",
        "--categoryExperimentalThirdParty=true"
      ]
    }
  }
}

Restart the MCP client after changing its configuration. Never claim that the server is usable until its browser tools appear. Mention that the server can inspect browser content and therefore must not be attached to a profile or page containing secrets or personal data.

Launch Chrome with the feature available

The experimental switch belongs to the chrome-devtools-mcp process, not to the Chrome executable. Let the configured MCP server launch Chrome normally; because its arguments include --categoryExperimentalThirdParty=true, the Chrome session it controls exposes list_3p_developer_tools and execute_3p_developer_tool to the agent. To verify the setup outside an MCP client, launch the server directly with the same switch:

npx -y chrome-devtools-mcp@latest --categoryExperimentalThirdParty=true

Do not invent or add a similarly named --chrome-arg: there is no separate Chrome browser flag for this integration. When attaching the MCP server to an already-running debuggable Chrome with --browser-url, --ws-endpoint, or --auto-connect, keep --categoryExperimentalThirdParty=true on the MCP server command line.

As of 2026-09-01 and chrome-devtools-mcp 1.8.0, third-party developer tools are experimental, disabled by default, and subject to API changes. Before configuring a newer release, run npx -y chrome-devtools-mcp@latest --help and consult the upstream guide. If the feature has graduated or the option has been renamed or removed, follow the current upstream interface rather than forcing this historical experimental switch.

Prepare Prebid.js

1. Open or navigate to the target page with Chrome DevTools MCP.

2. Enable Prebid debugging in page context if it is not already enabled:

   () => {
     window.pbjs?.setConfig({debug: true});
     return window.pbjs?.getConfig('debug');
   }
   

   Adapt pbjs to the page's Prebid global when necessary. Prefer the page's known global over guessing.

3. Wait briefly for devtoolsMcp-standalone.js to load. A build that includes devtoolsMcp installs it directly; otherwise debug mode triggers its on-demand standalone loader.

4. Call list_3p_developer_tools. Expect a group named Prebid.js DevTools with summary, auctions, and events.

If discovery fails, check in this order:

• Confirm that the MCP server was started with --categoryExperimentalThirdParty=true.
• Confirm debug is true on the correct Prebid global.
• Inspect the console and network panel for a failed request for devtoolsMcp-standalone.js.
• Confirm the page uses a Prebid.js build containing the integration introduced by prebid/Prebid.js#15356. For a custom or older build, include the devtoolsMcp module or update the build.
• Navigate or reload after correcting setup, then call list_3p_developer_tools again; discovery runs after navigation and on an explicit list request.

Do not use window.__prebidDevToolsMcp as the normal interface. It is an implementation detail useful only for diagnosing installation.

Invoke Prebid Tools

Call execute_3p_developer_tool with the exact tool name and a JSON-stringified object in params. Start broad, capture identifying values, then narrow subsequent calls.

summary

Use first to inventory each Prebid instance, its version, installed modules, configuration, aggregate counts, bidder bid/win/no-bid counts, and latest auction.

toolName: summary
params: {}

Every result is tagged with instance. On multi-instance pages, pass that value back as a filter:

toolName: summary
params: {"instance":"pbjs"}

auctions

Use to inspect eligible bid requests, received/rejected/winning bids, no-bids, floors, auction metrics, and TTL/cache timing.

toolName: auctions
params: {"instance":"pbjs","auctionId":"<auction-id>"}

Omit either filter to include all matching instances or auctions. Compare eligibleBidRequests, bidsReceived, noBids, bidsRejected, and winningBids rather than inferring a failure from one count alone. For cache problems, inspect bufferedTTL, effectiveMinCacheTTL, expiresAt, cacheExpiresAt, timeToExpire, timeToCacheExpire, and usableForTargeting.

events

Use to reconstruct chronological Prebid behavior and correlate it with auction details.

toolName: events
params: {"instance":"pbjs","auctionId":"<auction-id>","limit":100}

Filter by eventType when testing a specific transition, for example auctionInit, auctionEnd, bidResponse, or bidWon. limit selects the most recent events across all selected instances and defaults to 100. Increase it deliberately when earlier events matter; avoid dumping unbounded histories.

Diagnose Systematically

1. Run summary and select the relevant instance and latest auctionId.
2. Run auctions for that instance and auction.
3. Run events with the same filters and a bounded limit.
4. Use standard Chrome DevTools MCP network and console tools to validate any hypothesis suggested by the Prebid data.
5. Report observations separately from conclusions. Include instance, auction ID, bidder/ad unit, relevant timestamps, and the evidence that supports each conclusion.

Prefer these page-provided tools over large evaluate_script expressions. Use evaluate_script with window.__dtmcp.executeTool(toolName, params) only when composing a result with page-side logic or handling a value the standard tool cannot serialize.

Respect Boundaries

• Treat all returned configuration, bid, and event data as potentially sensitive; disclose only what the task requires.
• Keep investigation read-only unless the user explicitly asks to change page state. Enabling debug is the sole routine mutation in this workflow.
• Do not mistake missing historical data for proof that an event never occurred; Prebid retains runtime records for a limited lifetime.
• Re-run discovery after navigation because third-party tools are scoped to the current page and origin.
• State clearly when setup is blocked by a missing browser, missing MCP tools, an unsupported Prebid build, or a failed standalone-bundle load.

For upstream behavior changes, consult the Chrome third-party developer tools guide and the initial Prebid.js integration.