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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), so the bar is lower, and the description still adds real context: inline image data is placeholder-substituted by default, and an Indie plan is required (trial counts). It stops short of explaining pagination or response size limits, but the placeholder behavior is exactly the kind of non-obvious trait worth disclosing.

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 tight sentences, front-loaded with what is returned and the default placeholder behavior. The trailing '(trial counts)' clause is slightly cryptic but not wasteful; nothing else could be cut without losing information.

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 burden of describing the return payload, and it does so at a useful level of abstraction (layout JSON plus locale-keyed translation overrides). The plan requirement is a genuine prerequisite an agent needs. Only minor gaps remain around response size or pagination behavior.

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%, and the schema's include_image_data description is more complete than the tool description, including the update-rejection consequence of placeholders. The description's mention of placeholders echoes rather than extends the schema, so baseline 3 applies.

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 ('Fetch') and resource ('a screenshot set') and enumerates exactly what comes back: every screen's layout JSON plus per-screen translation overrides keyed by locale. This clearly distinguishes it from sonar_list_screenshot_sets, which would return summaries rather than the full payload.

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?

Usage is implied rather than stated: an agent can infer this is the detail-fetch counterpart to the list tool, and the description notes an 'Indie plan' prerequisite. But it never says when to choose this over the list tool or names an alternative, leaving routing to inference.

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