Elicitation

This guide explains how a client handles elicitation requests sent by the MCP server.

Enabling Elicitation Support

let mut client = Client::new()
    .with_options(|opt| opt
        .with_elicitation(|e| e
            .with_form()
            .with_url()));

This enables:

• Form-based elicitation
• URL elicitation

Handling Elicitation Requests

Define an elicitation handler using the #[elicitation] attribute macro.

#[json_schema(ser)]
struct Contact {
    name: String,
    email: String,
    age: u32,
}

#[elicitation]
async fn elicitation_handler(params: ElicitRequestParams) -> ElicitResult {
    match params {
        ElicitRequestParams::Url(url) => {
            // Follow the url to perform the external action.

            ElicitResult::accept()
        }
        ElicitRequestParams::Form(form) => {
            // Show the form to a user to fill in the data

            let contact = Contact {
                name: "John".to_string(),
                email: "john@email.com".to_string(),
                age: 30,
            };

            elicitation::Validator::new(form)
                .validate(contact)
                .into()
        }
    }
}

What Happens Here?

• URL elicitation
  • Client accepts and performs the action externally
• Form elicitation
  • Client constructs data
  • Data is validated against the server schema
  • Validated payload is returned as ElicitResult

к сведению

If you skip the with_elicitation() or with_form() or with_url() but declare the elicitation handler this will enable form elicitation by default.

Observing Elicitation Completion

client.on_elicitation_completed(async |n| {
    let Some(params) = n.params::<ElicitationCompleteParams>() else {
        println!("Unable to read params");
        return;
    };

    println!("Elicitation {} has been completed.", params.id);
});

This is useful for:

• UI updates
• Logging
• Tracking external flows (payments, auth)

Learn By Example

A complete working example is available here.