Screenshot on one screen

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

With readOnlyHint/openWorldHint already declared, the description adds real context: the PNG is written to captures/, a responsive audit runs in the same viewport and its findings are returned alongside the path, and returnImage is flagged as token-expensive. It doesn't mention network/permission caveats, but the token-cost warning and artifact-location disclosure go beyond the annotations.

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?

Front-loaded with the core action and artifact location, then the audit behavior, then call examples and the returnImage caveat. Four dense sentences with little waste, though the mixed Spanish/enum tokens make it slightly denser than ideal.

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?

Given 15 parameters, nested viewport/geolocation objects, and no output schema, the description does the necessary work of stating the return shape (PNG path in captures/ plus audit findings) and the expensive optional image path. It stops short of explaining how its viewport audit relates to the dedicated responsive siblings.

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% across all 15 parameters, so the schema already carries the bulk of the semantics and the 3 baseline applies. The description adds marginal value by showing typical request shapes, pointing at list_devices for device ids, and clarifying the token cost of returnImage.

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: opens a URL in the local browser emulating ONE concrete screen and saves a PNG, plus runs a responsive audit. The emphasis on 'UNA pantalla' implicitly differentiates it from multi-screen siblings, but no sibling is named, so the contrast is left to inference.

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?

Provides concrete call shapes ({ url, device: "iphone-15-max" } and { url, viewport: {...} }) which imply usage, and warns to set returnImage=true only when the image is actually needed. However, it never says when to pick this over check_responsive, preview_devices or the session-based siblings, so the routing decision is left implicit.

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