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

With no annotations, the description carries the full burden. It discloses that the tool is browser-based, takes size/weight input, and auto-determines the cheapest method, but it does not elaborate on how the user interacts with it, whether data is submitted externally, or what the output format is beyond a recommendation.

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, compact sentence that uses an arrow to convey the input-to-output workflow. It is front-loaded with the core function and includes a useful 'Browser-based tool' note. No redundant information.

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 the tool's simplicity (0 params, no output schema), the description is reasonably complete: it states input, processing, output, and the browser-based nature. It lacks explicit guidance on when to use it versus alternatives, but that is covered under usage guidelines. Overall, it provides enough context 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?

There are zero parameters in the schema, so the description needs to explain conceptual inputs. It does mention 'サイズ・重さ入力' (size/weight input), adding meaning beyond the empty schema. This compensates for the absence of formal parameters, though it lacks specific units or dimensions.

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 action: automatically determine the cheapest Mercari shipping method based on size and weight input, and compares all shipping methods. This distinguishes it from generic tools like shipping-calculator or mercari-calculator by focusing on Mercari-specific shipping comparison.

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 a clear use case: when a user has size and weight details and needs the cheapest shipping method for Mercari. It does not explicitly mention alternatives or exclusions, but the context is clear enough for an agent to select it appropriately.

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