Developer
What is a machine door, and how do you put one on an existing service?
The door is a file, not a rebuild. The engineering is in what the file refuses to say.
The answer
A machine door is a discovery document served at a well-known path that tells an agent who is accountable for an organisation, which actions it may take, where each lives, what it costs and how to pay — without a human reading the website. You put one on an existing service by publishing that one file; it describes the service rather than replacing it, so it is the lowest-cost way onto the agentic internet.
What the file has to get right
Capabilities are verbs an agent can act on — quote, book, refund — never departments like sales or finance, which tell an agent who to talk to rather than what it can do. Prices are whole minor units beside an explicit currency; a float, a bare number, or a price with no way to pay is refused by the checker rather than served.
Every endpoint the door names must stay on the organisation’s own domain or a subdomain of it. A door may not point agents at another organisation’s endpoints, whatever the arrangement — the other organisation publishes its own door — and the rule refuses parents and siblings rather than guess at which suffixes are registrable.
Absent is not unreachable
A consumer fetching a door distinguishes a host that answered 404 (there is no door) from a host that did not answer at all (we could not reach it). Collapsing the two is the common integration bug, because "this organisation has no machine door" and "our fetch failed" need opposite responses.
The underlying concept is defined canonically at The machine door — FlashyOS. This page answers the build question; that page answers the “what is it” question.
Talk to the practice
Tell us what you are trying to build and what has to be true for it to work.
Contact