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

Annotations already cover the safety profile, but the description adds real behavior: results are scoped to one store, defaults apply when parameters are omitted, and the two stores return different device families (Apple vs Android). The trailing 'Read-only' merely restates readOnlyHint and the return format is not detailed.

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 usage trigger before the behavior details. Only waste is the closing 'Read-only,' which duplicates the annotation and could be dropped.

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 zero-required-parameter read tool with full schema coverage and clear annotations, the description supplies the store-scoping and default behavior an agent needs. Since no output schema exists, the enumeration of what is returned (devices, frame colours, canvas sizes) partially compensates, though the exact shape is left implicit.

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% and the enum is documented, so the baseline is 3, but the description goes further by explaining the semantic consequence of the store parameter (Apple devices vs Android phones) and the default-when-omitted behavior.

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 ('lists' the device frames, colours, and canvas sizes) plus the scoping unit ('for one store'). It also separates itself from the screenshot-set siblings by framing itself as the lookup you do 'before choosing a non-default device for a screenshot set.'

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 trigger conditions ('when the user asks which devices, frame colours or canvas sizes... or before choosing a non-default device'). It stops short of naming a sibling to prefer or an explicit when-not-to-use, so it is strong context rather than full routing guidance.

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