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

Annotations show readOnlyHint=false, destructiveHint=false, idempotentHint=false, and openWorldHint=false. The description says it 'produce[s] a third image', implying a new file is created. It does not specify whether this tool modifies any existing files or requires specific permissions, but it does not contradict the annotations.

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?

The description is concise and well-structured, with a clear summary paragraph followed by an Args section. Every sentence adds value without redundancy.

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?

Given 4 parameters, no output schema, and 17 sibling tools, the description covers purpose, parameters, use cases, and limitations. It is complete enough for an agent to decide when and how to invoke this tool.

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 has 0% description coverage, but the description fully explains all four parameters: 'before' and 'after' as screenshot paths, 'name' as output label, and 'threshold' with range (0-255) and default (25). It adds meaning beyond the schema's titles and defaults.

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 clearly identifies the tool as comparing two screenshots and producing a diff image with highlights. It uses specific verbs ('compare', 'produce') and distinguishes itself from sibling tools like 'screenshot' (capture) and 'observe' (check existence).

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 description provides concrete use cases (layout shifts, content updates, focus-ring changes, modal overlays, theme switches) and explicitly states what the tool does NOT do ('does not auto-judge whether a diff is a bug'). It lacks explicit alternatives or conditions to avoid using it, but offers strong contextual guidance.

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