Look at the screen

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true, so safety is covered. The description adds real behavioral context beyond that: the default excludes the terminal window, the screen target captures a whole display, and windows can be selected by app/title/id. It stops short of mentioning fallback edge cases or multi-display behavior in detail.

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?

Three compact sentences, front-loaded with the core action before the capture-target nuances. Little waste, though the target explanation mildly overlaps the schema's own description.

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?

No output schema exists, but the description states the return is an image, covering the output form. For a 5-param, all-optional read tool with a safe annotation, this is largely complete; only deeper fallback/multi-monitor nuances are absent.

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 100%, so each parameter is already documented in the schema. The description reinforces default behavior ('target "window"' by default) and the screen alternative, but adds no syntax or format detail beyond what the schema already provides. Baseline 3 is appropriate.

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?

Specific verb+resource: 'Take a screenshot of what the user is looking at and return it as an image.' This clearly identifies a screen-capture operation. It does not, however, differentiate itself from siblings like device_screenshot or select_region, which also capture visual content.

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?

It explains the default capture behavior (front-most non-terminal window) and how to switch to a whole display via target 'screen', which guides invocation. But it offers no guidance on when to prefer this tool over siblings such as device_screenshot or select_region, leaving alternatives to inference.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.