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

Annotations already provide safety hints (readOnlyHint=false, destructiveHint=false). The description adds that it requires two distinctly named uploads and produces a visual highlight of differences, which is useful context. It does not detail side effects, but the bar is lower given 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 two short sentences with no wasteful words; the purpose is front-loaded and the category tag is unobtrusive. It is appropriately concise.

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?

The schema fully documents all 7 parameters and defaults, and annotations cover the safety profile. The description clearly explains the tool's operation but does not explicitly state the return format; however, the output_format parameter description indicates that a diff image is returned, making it sufficient for invocation.

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's mention of separately-named uploads restates what the schema already shows via required fields. No additional parameter semantics are added beyond 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 clearly states a specific verb ('Compare') and resource ('two images'), and indicates the visual output. It does not explicitly distinguish from sibling tools like analyze_image_similarity, but the purpose is unambiguous.

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 implies the tool is for visually comparing two images, but it does not mention when to prefer this over sibling tools or state any exclusions. The 'Takes two separately-named uploads' line is more of a parameter note than a usage guideline.

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