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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered. The description adds real behavioral context beyond that: the static-vs-motion tradeoff and the guidance to prefer semantic snapshots, which shapes correct tool selection. It does not mention capture latency or fidelity limits, so not a full 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?

Two sentences, front-loaded with the triggering condition, then the sibling comparisons. Every clause earns its place and nothing is redundant with the schema or annotations.

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 the description fully covers selection guidance. For a 12-parameter tool with a complex anyOf target-selection structure, it could have briefly clarified the targeting alternatives, but the schema handles that adequately.

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 says a single window, monitor or rectangle is targeted but does not explain the anyOf selection modes (coords vs window_id vs pid vs app vs title vs monitor/monitor_index) or how they interact, leaving that entirely to the schema.

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?

The description states a specific capability (static pixels for visual verification) and scopes it to a single window, monitor or rectangle, so the agent immediately knows the resource and granularity. It explicitly contrasts itself with take_screenshot, record_screen, ui_snapshot and browser_snapshot, so it is distinguishable from siblings without opening any schema.

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?

It gives explicit when-to-use (static pixels needed, single region) and when-not (full desktop, motion/timing required), plus the alternative to prefer first for semantic structure. This is a full routing rule set rather than vague context.

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