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

Annotations already declare this is a non-destructive, idempotent write. The description adds genuinely new behavioral context beyond them: the account-verification prerequisite and the fact that unverified keys are blocked. It still omits duplicate/SKU-conflict behavior, which matters given idempotentHint=true.

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 sentences, purpose front-loaded, prerequisite at the end. The only waste is re-listing the full category enum that the schema already carries, but it's contained and the rest earns its place.

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 4-param tool with full schema coverage and an output schema, the description covers purpose, category, and auth prerequisites adequately. The remaining gap is duplicate/idempotent handling, which the annotations hint at but the description doesn't resolve.

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?

Schema coverage is 100%, so the schema already documents sku, name, brand, and category. The description only restates the category enum verbatim and adds no syntax, format, or constraint meaning beyond what the schema provides; baseline 3 applies.

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?

States a specific verb and resource with scope: 'Add a product to this API key's inventory.' The inventory-scoping cleanly distinguishes it from add_watch_pattern and add_* siblings, so an agent can tell what it does without opening a schema.

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?

Gives real operating context: a verified account is required and unverified signup keys cannot add inventory, which steers usage. However, it never names alternatives (e.g. lookup_product before adding, or add_watch_pattern to track) or states when *not* to use it.

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