Same page on many screens

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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds real context beyond that: one PNG per device including horizontal overflow, a parallelism cap of 4, and the default device set. It omits auth/permission requirements and rate limits, keeping it short of 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?

Four sentences, front-loaded with the core action, then output, then default behavior, then the routing alternative. Each sentence carries distinct information with no filler.

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 13-parameter tool with no output schema, the description covers the return value (PNG per device plus overflow), the default device behavior, and the sibling alternative. Parameter details are fully carried by the 100% schema coverage, so the only minor gap is that permissions/auth context is not mentioned.

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 the baseline is 3. The description earns above that by naming the concrete default device ids (iphone-15-max, galaxy-s24, ipad-pro-11, laptop, desktop-hd) and restating the 'up to 4 in parallel' constraint tied to concurrency, adding meaning the schema only alludes to.

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 ('Captura la MISMA URL en varias pantallas') plus the output (un PNG por dispositivo con el desborde horizontal). It explicitly differentiates from sibling check_responsive and implicitly from screenshot_on by contrasting scope.

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 the exact use-case question it answers ('como se ve esto en movil, tablet y desktop') and names the alternative check_responsive with the condition that selects it (only need to know where the layout breaks, no images downloaded). Nothing is left to inference.

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