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

Annotations already declare read-only, idempotent, non-destructive, closed-world behavior, so the safety profile is covered. The description still adds meaningful context beyond that: it reports units only, not money/balances, and clarifies it reads Amazon's own Unreconciled Quantity column rather than deriving a shortfall from a formula. It stops short of describing pagination or row limits.

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 critical 'UNITS ONLY' scoping, then purpose, then usage, then the prerequisite. Dense but every clause carries information; only the parenthetical about money could be trimmed slightly.

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?

With no output schema, the description usefully sketches the return shape (Amazon's reference id per row plus ledger event totals in units) and the source column. It is nearly complete, though it doesn't state result limits or ordering for the row list.

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 all four parameters (sku, days, account, marketplace_id) are already documented in the schema. The description reinforces the marketplace_id requirement and the single-marketplace scope but adds no format or syntax detail beyond what the schema provides, so the 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 (unreconciled units in Amazon's own Inventory Ledger) and immediately distinguishes itself from get_payout_balance with the 'UNITS ONLY' scoping. An agent can tell exactly what this returns without opening the 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 explicit trigger phrases ('am I missing units', 'is Amazon holding stock it never accounted for') and an explicit exclusion plus alternative ('use get_payout_balance for money'). It also states the prerequisite ('Requires a marketplace id from list_my_marketplaces').

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