diff_frames

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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds behavioral detail: pixel-by-pixel comparison and the output of a changed region plus a ratio. This goes beyond the annotations without contradicting them.

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 a single, efficient sentence with no filler. It front-loads the core operation and the output, making it easy to scan and understand quickly.

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?

An output schema exists, so return values do not need to be described. However, the missing input format details and lack of guidance on edge cases like mismatched image sizes make the description incomplete for confident invocation. It is adequate but has a clear gap.

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?

The schema only defines two required strings with no format, and schema description coverage is 0%. The description identifies the parameters as 'PNG frames', which adds some meaning, but it does not clarify whether frame_a and frame_b are file paths, data URIs, raw byte strings, or something else. This leaves a critical ambiguity for the agent.

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 uses a specific verb ('Compare'), identifies the resource ('two PNG frames'), and states the result ('changed region and ratio'). This clearly distinguishes it from sibling tools like read_image or run, which perform different operations.

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 purpose implies when it should be used: whenever two PNG frames need to be compared. However, there is no explicit guidance about when to use this tool instead of alternatives, no exclusions, and no mention of prerequisites such as matching dimensions or format.

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