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

Annotations already declare readOnlyHint=true; the description reinforces this by stating 'It does not buy anything.' It adds valuable behavior beyond the annotation by disclosing the fallback: returns a reason when no checkout is configured.

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?

Three short, front-loaded sentences. The first identifies the resource and context; the second covers the edge case; the third clarifies side effects. No redundant or unnecessary content.

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 single-parameter read-only tool with full schema coverage, the description covers purpose, edge-case behavior, and side-effect clarification. Nothing essential is missing for correct 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?

The input schema fully describes the only parameter (slug as 'The product slug.'), so schema coverage is 100%. The description does not add extra semantics for the parameter, meeting the baseline for high coverage without adding further detail.

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 (get) and resource (checkout link for a product), and clarifies it is the link used by the Buy button. It distinguishes from purchase actions by explicitly noting it does not buy anything, and from sibling search/product tools by focusing on checkout links.

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—this is the link used by the Buy button and returns a reason when checkout is not configured. It implies when to use it (when you need a product's checkout link) but does not explicitly mention alternatives or when not to use it, leaving sibling differentiation implicit.

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