# Structured output

> Rowe returns typed output objects for tasks such as fit checks, placement, stability, prediction, reconstruction, action, and optimization. Four Cad consumes reasoning_scene.v2 inside those outputs to render objects, relation lines, collision volumes, support patches, measurements, issue regions, fit results, comparisons, geometry changes, and grounded text.

Source: https://fourechelon.com/docs/structured-output · Machine-readable: https://fourechelon.com/openapi.json · Index: https://fourechelon.com/llms.txt

## Typed, not prose

Every task returns a typed object rather than a paragraph to parse. A fit check returns a verdict, a clearance number, and the entities responsible; it does not return a sentence describing them.

## reasoning_scene.v2

Spatial outputs can carry a renderable reasoning layer: objects, relation lines, collision volumes, support patches, measurements, issue regions, comparisons, and geometry changes. Four Cad renders exactly this — there is no separate visualization format.

## Traceability

Findings reference the geometry they were computed from. That is what makes a result reviewable rather than something to take on trust, and it is the reason we keep the structure instead of flattening it.

## Response fields

| Field | Type | Description |
| --- | --- | --- |
| id | string | Unique response id. |
| object | string | The object type. Usually response. |
| model | string | The model that generated the response. |
| output | array | Typed spatial outputs for the requested task. When the request carried a cad_scene, understand, describe, and compare add output[].data.cad_scene: named objects with absolute bounds and parents, connectors with direction, spatial relations, title block, and callout counts; compare adds output[].data.cad_scene_diff (added, removed, moved, re-parented, rewired, dimensions changed). |
| usage | object | Input spatial tokens, output spatial tokens, projected input cost, projected output cost, and total estimated cost. |
| request_id | string | Request id for support and debugging. |