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

Annotations already declare readOnlyHint=true, indicating a safe read operation. The description adds the REST endpoint reference but no additional behavioral context such as authentication requirements, error conditions, or return format. It does not contradict annotations, but it also does not enrich beyond 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, complete sentence that clearly states the action and resource, with no wasted words. It also includes a precise REST endpoint reference, which is useful for developers without bloating the text.

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?

This is a simple read-only lookup tool with only two parameters and no output schema. The description, combined with full schema coverage and readOnlyHint annotation, provides sufficient context for an agent to invoke the tool correctly. A perfect score would require a bit more detail on expected response structure or error handling, but for this complexity it is nearly 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?

The input schema has 100% description coverage for both parameters ('id' and 'product_id'), so the description does not need to add parameter details. The description's mention of 'by id' adds minimal extra meaning but does not compensate for anything missing, so baseline 3 is appropriate.

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 ('Get') with a clear resource ('a single variant category on a product') and identifies the lookup method ('by id'). It distinguishes from sibling tools like 'gumroad_list_variant_categories' and 'gumroad_get_product' by specifying the exact resource and identifier.

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 clearly implies when to use this tool: when you need a specific variant category by ID, as opposed to listing all categories (gumroad_list_variant_categories). It does not explicitly state exclusions or alternatives, but the context is clear from the tool name and sibling list.

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