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

Annotations indicate readOnlyHint and openWorldHint. The description adds useful behavioral context, particularly the warning 'Never send variant_id as a number' and the format requirement. However, it does not disclose response format or error behavior, which would be valuable for a tool with no output schema. The input-specific disclosure goes beyond annotations but lacks richer behavioral detail.

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 three concise sentences: a usage trigger, required arguments with an example, and a critical formatting warning. Every sentence adds value with no redundancy. The structure is front-loaded with the purpose and immediately gives actionable details.

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 description covers the primary use case and main parameters, but given there is no output schema, it omits what the response contains. It also leaves the five optional parameters unexplained, though they may be less critical. For a tool of moderate complexity, the description is adequate but 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?

With 0% schema coverage, the description compensates meaningfully. It explains the required parameters (destination_postal_code, country, items) and gives an example, plus the critical constraint that variant_id must be a string. The optional parameters (journey_id, match_type, etc.) are not described, but the core usage for shipping estimates is well covered.

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 the tool's purpose: 'Use when the buyer asks shipping cost for selected catalog variants.' It specifies the resource (shipping cost) and the verb (get). However, it does not explicitly differentiate from sibling tools like get_pricing, though the focus on shipping cost and catalog variants provides reasonable distinction.

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 provides clear when-to-use guidance: 'Use when the buyer asks shipping cost for selected catalog variants.' It also specifies required arguments, establishing context for use. It does not mention exclusions or alternatives, but the instruction is direct and actionable.

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