Forms as declarative tools

WebMCP also proposes a declarative API: a form carrying toolname and tooldescription, with fields named by name and described by toolparamdescription, is a tool the browser derives from the markup. The browser fills the fields and submits; the person can see the form as it is filled. formTool draws a capability that way, from the same contract, so the form and the registered tool cannot name or describe it differently:

const CreateTodoForm = AgentWebMcp.formTool(AppAgent, 'requested_create_todo')

// In the view: the form and each field the input names. `DraftSubmitted` and
// `model.draft` are the application's own submit and draft, as before.
h.form([...CreateTodoForm.form(h), h.OnSubmit(Message.DraftSubmitted())], [
  h.input([...CreateTodoForm.field('title', h), h.Value(model.draft)]),
])

// Beside `register`, which then answers the form's agent submissions.
AgentWebMcp.register({ agent, forms: [CreateTodoForm] })

formTool only writes attributes; it registers nothing and listens to nothing. register({ forms }) listens for submit on the document in the capture phase, ahead of the application's own handler. A submission the browser marks agentInvoked is answered as the tool call would be: the fields the input names are read from the form as text, decoded, authorized and dispatched as the capability, and the result goes back through respondWith. The application's OnSubmit does not run for it, so an agent's submission never depends on the Model having seen the browser fill the fields. A person's submission is the application's as before.

In a browser whose SubmitEvent has agentInvoked (AgentWebMcp.declarativeTools()), a form's capability is not also registered imperatively, since the form is the tool. Elsewhere it is registered as usual. A field's value arrives as text, as every form submits it: give such a capability text fields, or a transforming Schema (Schema.NumberFromString). The declarative API is an early proposal whose form-to-schema rules are still open, so treat it as a second way in, not the only one.

formTool(definition, name, { autosubmit: true }) adds toolautosubmit, which lets the agent submit without the person's review. It throws for a name the contract does not expose and for an input that is not an object of fields; field throws for a key the input lacks, and its type takes only the input's keys.