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

Annotations already declare readOnlyHint=true, openWorldHint=false, destructiveHint=false, so safety is covered. The description adds real operational context the annotations cannot: the vision-model size limit on full-page captures and the above-the-fold truncation behavior of preview. It does not cover failure modes or rate limits, so not a 5.

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 sentences, front-loaded with the core action and no redundant restatement of the name. The closing clause 'so you can see the UI' is mild filler, keeping it below a 5.

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, so the description carries the return-value burden, and it does so adequately (an image, possibly truncated or oversized). With annotations covering safety and the schema covering params and defaults, only error/edge-case behavior is missing.

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 the baseline is 3, but the description goes beyond the schema by explaining the above-the-fold/4000px semantics of preview and the vision-model constraint on full, which the enum description alone does not convey.

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+resource (get the actual screenshot of a screen) and explicitly differentiates from the sibling get_screen, which 'lists the page's sections with their y offsets.' An agent can tell the image-fetch tool apart from the metadata-list tool without opening either schema.

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 explicit conditions: preview (default) returns only above-the-fold content for tall marketing pages (>4000px), use size=full for the whole page, and route to getScreen when you need to know what is below the fold. When-to-use, when-not, and the alternative are all named.

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