Structured Output Is Still Model Output

Wed, 02 Sep 2026 16:45:00 +0100

JSON feels safer than prose because software can parse it.

That is a real advantage. It is not a guarantee that the values are correct, permitted or useful.

A model can produce perfectly valid JSON containing a nonexistent file, an unsupported operation, a reversed date range or an action the user never authorized.

Structured output is still model output.

1. Structure removes one class of ambiguity

Suppose we ask a model to choose a fixture and repetition count. Prose might return:

Expose the First WebMCP Tool

Wed, 02 Sep 2026 17:15:00 +0100

Our first WebMCP tool should not send a message, edit a document or buy anything.

It should read from the book we control.

We will expose search_book: a bounded operation that finds relevant chapters and passages.

1. Start with a narrow contract

Conceptually, the page registers:

navigator.modelContext.registerTool({
  name: "search_book",
  description: "Search this book for passages related to a query.",
  inputSchema: {
    type: "object",
    properties: {
      query: { type: "string", minLength: 2, maxLength: 300 },
      limit: { type: "integer", minimum: 1, maximum: 10 }
    },
    required: ["query"],
    additionalProperties: false
  },
  execute: ({ query, limit = 5 }) => searchIndex(query, limit)
});

WebMCP is evolving, so the exact registration surface must be checked against the browser version used for an experiment. The durable architecture is name, description, schema and implementation.

JSON Schema on Programmer.ie: Modern AI programming

Structured Output Is Still Model Output

1. Structure removes one class of ambiguity

Expose the First WebMCP Tool

1. Start with a narrow contract