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

Annotations already establish that this is a safe, idempotent, read-only lookup. The description adds meaningful behavioral detail beyond that: the exact status categories and the 'a dozen or fewer' threshold for 'low', which an agent could not infer from the annotations alone. It does not cover data freshness or why 'unknown' occurs.

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?

Two tight sentences, front-loaded with the outcome categories and followed by the invocation rule. There is no filler and every clause carries 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?

There is no output schema, so the description must explain return semantics, and it does by listing the four possible statuses. The main remaining ambiguity is what happens if both SKU and slug/color/size are supplied, or what 'unknown' signifies operationally.

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 required parameters and only 50% schema description coverage, the description supplies the critical dependency rule: use either a SKU alone, or a slug together with color and size. This clarifies how the four optional parameters combine in a way the schema does not enforce.

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 check: whether one variant is available now, and enumerates the possible statuses (in_stock, low, out_of_stock, unknown). This clearly separates it from siblings like build_cart, search_catalog, and quote, though it doesn't explicitly name them.

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?

Usage is implied by the availability-checking purpose, and the description tells you how to identify the variant (SKU or slug+color+size). However, it never states when to call this versus get_product or when availability should be re-checked, nor does it exclude any scenarios.

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