visual_compare

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

The annotations are all false, so they don't provide a strong safety profile. The description adds that the tool 'Returns metrics + a highlighted diff image' and notes the size-matching requirement, which is useful. However, it doesn't disclose whether the operation has side effects or how it uses the lease, leaving some behavioral ambiguity.

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 exceptionally concise, using four short sentences each delivering a distinct piece of essential information: action, return value, constraint, and prerequisite. There is no wasted wording, and the primary verb is front-loaded.

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 tool with no output schema, the description conveys the main return value (metrics + diff image) and key constraints. However, it omits any explanation of the threshold parameter and doesn't detail what metrics are returned, which leaves some gaps. Given the tool's moderate complexity, a slightly richer description would be more 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 description coverage is 0%, so the description must compensate. It clarifies that lease_id is required and that artifact_id_a and artifact_id_b are the two PNG artifacts. However, the threshold parameter is not mentioned at all, leaving its meaning undocumented. Since the description doesn't cover all parameters, it only partially compensates for the schema's lack of descriptions.

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 starts with 'Pixel-diff two PNG artifacts,' which clearly identifies the specific verb (pixel-diff) and resource (two PNG artifacts). This distinguishes it from sibling tools like visual_capture and visual_get, and the mention of returning metrics and a diff image further clarifies the purpose.

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 gives clear context by stating 'Sizes must match' and 'Requires lease_id,' which are important preconditions for use. However, it doesn't explicitly say when not to use this tool or name alternative tools, so it doesn't fully cover exclusion guidance.

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