Stall library · Discover
The UCP manifest cannot be read by agents
An unreadable UCP manifest is a file at /.well-known/ucp that claims to describe what a store supports under the Universal Commerce Protocol but breaks rules the specification sets for every manifest, such as a missing version or a missing services list. An agent platform reads this file before it tries anything else, so a broken one advertises a checkout the platform cannot find its way to.
Why the agent stops
The Universal Commerce Protocol starts with discovery. Before an agent platform checks out on a store over UCP, it fetches the manifest, picks a version both sides support, and reads which services and capabilities are on offer and where to reach them. A file it cannot parse, or one with no dated version or no services list, leaves it nothing to negotiate with.
What happens next is up to the platform. The likely outcome is that it treats the store as one without UCP and falls back to reading the storefront, which is why this is reported at medium severity rather than high: the store is harder to transact with, not invisible.
Having no manifest at all is not this finding, and Ottom does not report it as a defect. Whether a store has one is mostly decided by its platform, and a missing file is not something most merchants can or need to fix.
How often we see this
Not stated here. A frequency means nothing without the cohort it was counted over, and this page is about one stall rather than one category. Where a category has enough stores measured at every stage, the share of them showing this stall is published on its benchmark page, with the methodology beside it.
See it for yourself
- Open https://yourstore.com/.well-known/ucp and check it returns JSON rather than a web page.
- Check the document has a ucp object with a version written as a date, for example 2026-08-25.
- Check ucp.services is present, and that each service entry names a version and a transport of rest, mcp, a2a or embedded.
- Check every endpoint in it is an https URL.
What to change
- If your platform generates the file, do not edit it by hand. Raise it with the platform, since every store on it is likely affected.
- If you publish it yourself, validate it against the specification at ucp.dev for the version it names.
- If you are not ready to support UCP, remove the file. No manifest is a neutral answer. A broken one is a promise the store does not keep.
What Ottom looks at
Ottom requests /.well-known/ucp once per scan and reads the body, not the content type, so a web page or a bot challenge served at that address is never mistaken for a manifest. The finding is raised only when the body presents itself as a UCP manifest and breaks one of the rules above.
Questions
Does Ottom mark my store down for not having a UCP manifest?
No. Ottom records whether a store publishes one and shows it on the report, but a missing manifest raises no finding and costs no points. Only a manifest that is published and broken does.
Does a valid UCP manifest mean agents can buy from me?
Not on its own. The manifest describes what you support. Whether an agent platform will use it also depends on that platform, and Google, for one, says not every feature in the specification is available on its surfaces yet.