Prompt DSL for defining MCP prompt templates.

Prompts are reusable templates that generate messages based on provided arguments. They enable structured, parameterized interactions with LLM clients.

Examples

defmodule MyApp.MCP do
  use Ectomancer, name: "my-app", version: "1.0.0"

  prompt :analyze_churn do
    description "Analyze user churn over a time period"
    argument :days, :integer, required: true, description: "Days to look back"
    argument :threshold, :float, default: 0.05, description: "Churn threshold"

    messages fn args ->
      [
        %{
          role: "user",
          content: %{
            type: "text",
            text: "Using the list_users tool, analyze churn over the last #{args.days} days with threshold #{args.threshold}..."
          }
        }
      ]
    end
  end

  prompt :summarize_reports do
    description "Summarize recent reports"
    argument :report_type, :string, required: true,
              description: "Type of report",
              enum: ["sales", "inventory", "employee"]

    messages fn args ->
      report_type = Map.get(args, "report_type", "sales")

      [
        %{
          role: "system",
          content: %{
            type: "text",
            text: "You are a report analyst. Summarize the #{report_type} reports."
          }
        },
        %{
          role: "user",
          content: %{
            type: "text",
            text: "Provide a concise summary of the latest #{report_type} reports."
          }
        }
      ]
    end
  end
end

DSL Functions

• description/1 — Human-readable description of the prompt
• argument/3 — Define an argument with name, type, and options
  • :required — Whether the argument is required (default: false)
  • :description — Description of the argument
  • :default — Default value if not provided
  • :enum — List of allowed values
• messages/1 — Callback fn args -> [...] end that returns a list of message maps Each message is %{role: "user"|"assistant"|"system", content: %{type: "text", text: "..."}}

Arguments

Arguments support the following types: :string, :integer, :float, :boolean, :list, :map, and arrays ({:array, inner_type}).

Arguments with required: true will be validated by Anubis MCP before calling the messages callback. Missing required arguments will return a protocol error.

Response Format

The messages callback should return a list of message maps. Each message must have:

• :role — One of "user", "assistant", or "system"
• :content — A map with :type ("text") and :text (the message content)

The generated module wraps these messages in an Anubis.Server.Response struct with type: :prompt for proper MCP protocol encoding.