Cua Driver MCP tool output format

Every call keeps the standard MCP ToolResult envelope:

• content contains human-readable text and optional images;
• structuredContent contains the machine-readable successful result;
• isError distinguishes tool failure from a successful outcome.

Text is diagnostic, not a stable parsing API.

Action tools

Successful pointer, keyboard, value, and browser-input actions return the closed shared ActionResult in structuredContent:

{
  "effect": "unverifiable",
  "route": "global_input",
  "delivery": {"mode": "foreground"},
  "escalation": {"target": "page", "reason": "effect_unconfirmed"}
}

Do not parse platform route names, coordinates, targets, or the removed verified bit from text. Use effect, route, delivery, evidence, and escalation, then call verify_state or take a fresh snapshot for the task postcondition. See Action results and postcondition verification.

Observation and state tools

Observation tools retain their typed tool-specific structured payloads. get_window_state, for example, returns the accessibility outline and element records in structuredContent and can attach a PNG as image content. A multimodal harness interprets the image; Cua Driver does not OCR it or assign task meaning.