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

Annotations already declare non-idempotent, non-readonly, non-destructive behavior; the description adds concrete meaning by explaining the accumulation semantics ('calling it again adds more units') and the subscription behavior at the recommended shipping interval. It also notes the cart is the same as the SuppCo app, but omits any auth/permission requirements.

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?

Front-loads the action and target, then layers in input sourcing, the subscription flag, return value, and the accumulation caveat with its alternative. Every sentence carries information and none is redundant.

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?

An output schema exists, so the description need not detail the returned cart; it still mentions 'Returns the updated cart.' Combined with full parameter coverage and sibling routing, nothing an agent needs to call this correctly is missing.

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 baseline is 3; the description earns extra by clarifying that subscription routes to the product's recommended shipping interval and that product_id_or_slug must resolve to a Buying Club product. That adds meaning beyond the schema's terse field notes.

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?

Specific verb ('Add') plus resource ('a Buying Club product to the signed-in user's cart') with explicit scope ('only Buying Club products can be added'). It clearly distinguishes itself from sibling cart tools and names the discovery tools that provide valid inputs.

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?

States where to get inputs (suppco_find_buying_club_products, suppco_compare_to_buying_club) and explicitly names the alternative for a different intent ('to set an exact quantity, use suppco_update_cart_item'). When-to-use and when-to-use-something-else are both covered.

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