image_compare

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

The description is consistent with annotations (destructiveHint=true is explained by saving a diff PNG), and the caveat that metrics don't establish semantic/material correctness is genuinely useful context beyond the annotations. However, it omits where the file is written, whether an existing file is overwritten, and what the returned metrics actually are.

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 core action and followed by the key caveat. Every clause earns its place with no 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?

For a two-input tool with no output schema, the description covers purpose, output artifact, and a meaningful limitation, which is reasonable. It still leaves parameter roles and the nature of the 'metrics' it references unexplained, so it is not fully complete.

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 0% with two undocumented string params. The description contributes only the 'same-size' constraint and never maps reference vs observed roles, so an agent gets little help on what each argument should contain.

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 verb (compare), the exact resource (two same-size images), and the output side effect (save an absolute-difference PNG). No sibling in the list performs image comparison, so an agent can immediately distinguish this tool from the viewer/UI/capture tools.

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 implies usage through the 'same-size' prerequisite and adds a caveat about metrics, but gives no explicit when-to-use/when-not guidance or workflow context. Adequate implied guidance, no real selection criteria.

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