screenshot_windowCapture a specific window's rectangle from the composited frame using its window ID, so you can inspect or verify GUI output inside a nested Wayland display.
Captures the window's rectangle from the composited frame.
| Name | Required | Description | Default |
|---|---|---|---|
| id | No | Display id from display_open. Optional when exactly one display is open. | |
| scale | No | ||
| window_id | Yes | Window id from the windows tool |
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description must carry behavioral disclosure. It mentions capturing from the composited frame, which adds some context, but it does not state whether the window must be visible/focused, what permissions are needed, failure behavior, or what the capture returns.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single front-loaded sentence with no filler. "from the composited frame" is useful context and nothing is wasted.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a screenshot tool with no output schema and no annotations, the description is incomplete. It does not explain the return value, output format, scale behavior, or failure modes, all of which an agent needs to invoke the tool confidently.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 67%; window_id and id are documented in the schema, but scale is undocumented. The description adds no meaning about scale, display selection, or how the parameters interact, so it does not compensate for the remaining gap.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description gives a specific verb and resource: capturing a window's rectangle from the composited frame. It is clear what the tool does, but it does not explicitly distinguish this from the sibling screenshot tool that likely captures displays or full screens.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
There is no explicit guidance on when to use this tool versus screenshot, windows, or wait_for_window. The phrase "window's rectangle" implies it is for window-specific captures, but no alternatives or conditions are stated.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.