MCP: when the assistant asks directly.
The next step after being found, explained simply.
The door: MCP explained simply
Important: Assistants do not connect to a door on their own. A user has to add it, or a provider lists it in its directory.
- Level 1 everywhere: llms.txt, structured data, clean HTML
- Build your own MCP door and connect it to Claude, ChatGPT (connectors) or Cursor
- In ChatGPT: one app per website, submitted to and reviewed by OpenAI. Before that you can test it in your own ChatGPT as a custom MCP server.
- Examples from Europe: Since June 2026 Qonto has made its business account accessible to AI assistants via MCP; the bank operates in eight European countries. Danske Bank is testing a door for business customers.
- Examples from Germany: mutify.de answers questions about events through its own door, with a link to buy tickets. The test in ChatGPT as a custom connection passed on 19 October 2026. The Fiperly website offers have their own door too.
- Gemini Spark, Meta Muse, Dots on the Pro plan
- Shopping and paying by agents for consumers (UCP, AP2)
What is missing is not the protocol but the always-on consumer agent and the purchase path.
Shop window or counter?
- It loads the page and pieces together from the text what it needs.
- Prices, dates or stock can be outdated or picked up wrongly.
- The operator has no influence on what gets taken along.
- It asks a clear question and gets a ready-made, current answer.
- The data comes straight from the operator's system.
- The operator decides which details, in what form, with which link.
How a request works
search_events · Hamburg · 20 km · SaturdayWhat a door contains
Tools
The questions the door answers, for example search_events or check_availability. Each tool has a short description so the assistant knows when to use it.
Resources
Fixed content to look things up, such as opening hours, price lists or terms and conditions.
Doorbell sign
A small file and a note in the llms.txt tell assistants that a door exists and where it is. Since 2026 there is an official, optional MCP extension for this, the Server Card: it describes the door and sits at the door's own address under /server-card. It is found via /.well-known/ai-catalog.json, an open catalog format that is still a draft. Only a few assistants read it so far. What reliably counts today is registration in the assistant's directory.
Who needs a door
Rule of thumb: A door is worthwhile when an offer can be queried and keeps changing. For a blog or a company site, stage 1 is enough.
Your own door in four steps
- Define the questions. Which two or three questions do customers ask again and again? Exactly these become the tools.
- Build the door. A small MCP server answers these questions from your own database. Official building blocks (SDKs) exist for common programming languages, for example Python and TypeScript.
- Put up the doorbell sign. State the door's address in
/.well-known/ai-catalog.jsonand in thellms.txt. - Make it known. Test first: in your own ChatGPT you can add the door as a custom MCP server. For the broad public, the next step is a listing in the provider's directory, for example at OpenAI or Anthropic. In ChatGPT that means one app per website, not per subpage. The route runs through
platform.openai.comwith a verified account, proof of the domain (a file at/.well-known/openai-apps-challenge), privacy policy and terms, test cases and a review by OpenAI. Important: approved means findable in the app directory, not automatically part of every answer. The user connects the app once; ChatGPT can also suggest it. Without that connection, Level 1 still counts: what the crawlers of Bing and OpenAI (OAI-SearchBot) read on your site.
Real example: mutify.de
mutify.de is Fiperly's event calendar for all of Germany. mutify has its own MCP door. It has been running since September 2026 and is tested with Claude and ChatGPT.
The door has three tools: termine_suchen finds events by place, radius and date. termin returns a single event. staedte lists the cities with events. The door is read only and needs no login. Every result comes with a link to mutify.de or to the ticket shop.
How to connect ChatGPT to mutify
- Open the page. In ChatGPT go to
chatgpt.com/pluginsand click “Add”. - Choose your own door. Click “Add custom MCP server”.
- Enter the details. Name: mutify. Server URL:
https://mcp-mutify.michael-bertelsenmedia.workers.dev/mcp. Authentication: none. - Confirm. Tick the box and click “Create”. Then just ask, for example: “What is on in Berlin this weekend?”
Custom MCP servers can only be added to ChatGPT with a paid plan. The menu names may differ slightly by language. Want a door like this for your website? Book a call or write to info@fiperly.de.
Put honestly
A door does not bring a single visitor on its own. Assistants do not connect to foreign doors by themselves. They are only used once a user adds them or a provider lists them in its directory.
Security
The door only hands out what the operator releases. A read-only door without customer data is common. Anything that changes something, such as booking or ordering, requires a login and the user's confirmation.
The door and the negotiation: who talks to whom?
For two agents to negotiate a shoe price, three connections are needed. The MCP door is the first and most important one, because without it the buying agent does not even know what the shop has.
An assistant asks and gets facts back: size 43 in stock? Slot free? Ticket price? MCP does not know what a cart is. It connects a shop just like a bank or a calendar.
Buildable in GermanyThis is where buying happens. Google's UCP (with Shopify, Etsy, Wayfair, Target, Walmart, backed by Stripe, Visa, Mastercard) covers catalog, cart, checkout and after-sale. ACP by OpenAI and Stripe is the second route. AP2 proves the human approved the amount.
Not enabled in the EUWhat is in stock, in size 43, in blue? What does it cost, when will it arrive? An order only if the shop offers that at its door itself.
Possible todayThe buying agent talks to the shop's selling agent: "I'll take it for 109 euros." Counter-offer, voucher, faster delivery. Machine to machine.
Only in trialsUCP handles cart and checkout, AP2 the mandate: the agent pays only up to the limit set in advance. Second route: ACP from OpenAI and Stripe.
USA, as of 17 October 2026Frequently asked questions about the door
Who is behind MCP?
MCP was introduced by Anthropic in November 2024 as an open standard. Meanwhile OpenAI, Google and Microsoft support it as well. Since December 2025 it has been hosted by the Agentic AI Foundation under the Linux Foundation and therefore belongs to no single company.
Does the door replace my website?
No. People still come through the site. The door gives assistants the facts, and the link in the answer leads back to the website, for example for buying tickets or booking.
What does a door cost?
The standard itself is free. Effort only arises for the small server and its upkeep. If you already have a database or an interface, you use it as the source.
Do I need stage 1 first?
Yes. The door builds on an understandable site. llms.txt and structured data help assistants find the site and its door and understand them correctly.
Read on
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