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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds real value by explaining the visual semantics (red = not selected, mask = white for selected), but says nothing about the proxy render, size limits, or why it is marked non-idempotent. Adequate but not rich.

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?

A single, front-loaded sentence with no wasted clauses; the purpose and both modes are established immediately. It could be marginally tighter but nothing is 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?

With an output schema present, return values need no explanation, and annotations cover the read-only safety profile. The description is complete for a preview tool; the only minor gap is not clarifying the non-idempotent hint or the max_px render cap.

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 descriptions already define overlay vs mask, so the schema carries the load. The description restates the same overlay/mask contrast but adds no new syntax, defaults, or format detail. Baseline 3 is appropriate.

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 ('See a saved selection') and immediately names the two render modes, so the agent knows exactly what it produces. It distinguishes itself from siblings like modify_selection or the generic preview by scoping to a *saved* selection, though it does not explicitly name an alternative.

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?

The phrase 'shows whether a selection caught what was meant before it is used' implies the verification-before-apply use case, which is useful context. However, there is no explicit when-to-use/when-not-to-use rule or named alternative, leaving the agent to infer the workflow position.

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