Check Engine / Fix it / MCP

How to audit your site from an AI assistant

By Matt Kerr·Published ·Updated

Check Engine speaks the Model Context Protocol, the standard AI assistants use to reach tools on your own machine. Point an MCP client at the copy of Check Engine you already own and you can ask it to audit a site in conversation, and get the findings back as structured data it can reason about: rather than a screenshot you retype.

Point your assistant at it

Check Engine serves MCP over stdio, so there is no server to run and no port to open. The client launches Check Engine itself, with one command and one argument.

Claude Code

One line in a terminal:

claude mcp add docket -- /Applications/Docket.app/Contents/Resources/docket/docket mcp

On Windows, use the engine inside your install folder instead: claude mcp add docket -- "C:\Users\YOU\AppData\Local\Docket\docket\docket.exe" mcp, with your own account name in place of YOU.

Claude Desktop

On a Mac, open ~/Library/Application Support/Claude/claude_desktop_config.json and add:

{
  "mcpServers": {
    "docket": {
      "command": "/Applications/Docket.app/Contents/Resources/docket/docket",
      "args": ["mcp"]
    }
  }
}

That path is the audit engine inside the installed app, not the app icon you click. On Windows the file is %APPDATA%\Claude\claude_desktop_config.json and the command is C:\\Users\\YOU\\AppData\\Local\\Docket\\docket\\docket.exe, with each backslash doubled because the file is JSON. Restart the client and Check Engine appears as a tool. Any MCP client works the same way: the command and the argument are all it needs.

ChatGPT

The ChatGPT desktop app can run it: OpenAI's documentation says the desktop app supports MCP servers, including ones that run as a local command. Open Settings, then MCP servers, add a server, choose STDIO, and give it the same command and the argument mcp. ChatGPT on the web cannot. There, custom connections are for business workspaces and need a public HTTPS server, and Check Engine runs on your own computer rather than on the internet.

Every tool answer on this page was produced by calling a shipped, notarised build on 3 November 2026 (the handshake, the tool list and what an unactivated copy returns), not a development checkout, which behaves differently in the one way that matters most here (see the licence section below). Your own copy reports its version in the MCP handshake, so you can check this page against what you actually have; if it disagrees, the page is wrong and we want to hear about it.

The tools

audit_site crawls a site and returns the score and every finding: how bad it is, which pages it affects, how long the fix takes and the change to make. It takes a url, and optionally max_pages, max_seconds and offline. A full audit is kept, exactly as one run in the app is, and appears in Reports.

Three more answer the questions people ask next, from the audits Check Engine has kept, without crawling again. get_last_report returns the most recent audit, or the most recent of one site. explain_finding takes a check id or a few words of a problem's title and returns that one problem in full: what is wrong, which pages, the fix and the markup to paste. compare_audits takes two audits of the same site, by default the two most recent, and says how the score and each area moved and which problems are new, fixed, worse or better.

list_checks takes no arguments and answers “what does Check Engine actually check?” without crawling anything. On this copy it returns all 99 checks across 13 areas.

Two details worth knowing, because they are choices rather than accidents. The page budget you ask for is the page budget you get. Check Engine will not quietly crawl five times more because the site answered quickly, which is what its own --adaptive default does when a person is watching. And offline turns off the optional checks (no PageSpeed call, no DNS lookup of your mail domains) though the link check and rendering still reach the sites your pages link to or load.

It is the same engine, and the same licence

Nothing about this is a cloud service. The crawl runs on your computer exactly as it does when you click the button, there is no API key, and there is no per-call charge. Your assistant is talking to the app you bought, not to us.

Which also means an unactivated copy gives your assistant the free version: the audit runs, and the result is the overall score, how many problems each area has and the top problem in full, with a note saying what the paid version adds. list_checks works either way, because it crawls nothing. A free audit is not kept, so the three tools that read kept audits have nothing to read until the copy is activated, and they say so. Activate once with checkengine licence --key YOUR-KEY, or in the app, and the audit tool returns every finding from then on. Check Engine is $59 once, so there is no seat to add for the assistant.

What it does not do

The MCP surface is deliberately small: five tools, not a wrapper around every command. It does not schedule audits or manage the watchlist, and it compares only audits Check Engine has kept, not two live sites side by side the way checkengine diff does. Those are in the app and the command line.

Common questions

Does Check Engine work with Claude Desktop?

Yes. Add Check Engine to mcpServers in claude_desktop_config.json with the command /Applications/Docket.app/Contents/Resources/docket/docket and the argument mcp, then restart the client. Any MCP client works the same way, because Check Engine speaks the protocol over stdio.

Does using Check Engine through MCP cost extra?

No. There is no API key and no per-call charge. The crawl runs on your own computer, the assistant is talking to the copy of Check Engine you bought, and the licence is the same one-time purchase.

Can an assistant audit a site if Check Engine is not activated?

Yes, the free version. The audit runs, and the assistant gets the overall score, how many problems each area has and the top problem in full with its fix. Activating the copy, in the app or with checkengine licence, makes the same tool return every finding.

Does Check Engine work with ChatGPT?

In the ChatGPT desktop app, yes: add Check Engine under Settings, MCP servers, as a STDIO server with the command above and the argument mcp. ChatGPT on the web cannot run it, because there custom connections need a public HTTPS server and Check Engine runs on your own computer.