Look at a window

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

Beyond the readOnly/idempotent annotations, it discloses genuinely non-obvious traits: the native capture works even when the window is covered, WebP capped at 1568 px, an unchanged image is not re-attached (except in mode image), and observations expire in 60 s. This is exactly the operational context annotations cannot carry.

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 purpose is front-loaded in the first clause and every clause carries information. It is a single dense semicolon-chained paragraph, which packs a lot into a small space but borders on overloaded for a reader scanning quickly.

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?

With no output schema, the description carries the return-value burden and does describe the two output shapes (tree fields, WebP image) and the caching rule. Remaining gaps are minor: it does not describe error behavior for an invalid or closed window, nor the exact size/format of the tree output.

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 description coverage is 100%, so every parameter including marks and region is already documented, making 3 the baseline. The description adds some meaning for image/both and the region-relative-to-last-image behavior, but it never mentions 'marks' and largely restates schema content for the rest.

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?

States a specific verb and resource ('See a window in the background, without bringing it forward') and immediately names the two payloads: UI Automation tree and optional native capture. It also differentiates itself from the sibling 'act' by declaring it selects the window that act will operate on.

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?

Gives clear context for each mode (text default, image, both) and an explicit lifecycle rule ('an observation serves one act and expires after 60 s'), which tells the agent when it must re-look. It references 'windows' as the source of window ids but does not explicitly contrast when to use 'look' vs 'window' or 'windows', so a small inference remains.

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