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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower. The description still adds real behavioral context: history only begins the day AgentXray first read the product (a data-availability constraint) and the domain note that lower rank is better, neither of which is in annotations or schema.

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 tightly written sentences: purpose and payload first, then the data-start caveat, then usage examples. Every clause earns its place, though the parenthetical about rank direction sits slightly awkwardly mid-description.

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 enumerates the return shape (per-day points, category, changes, state flag) and notes the historical start boundary. Annotations handle safety, so the remaining description is adequate, though pagination or result-size limits are unstated.

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 description coverage is 100%, so the schema already documents all six parameters (sku, days, account, end_date, start_date, marketplace_id). The description implies the daily-series granularity and the 7/30-day windows but adds no format or syntax detail beyond what the schema provides, making the baseline 3 correct.

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 resource (Best Seller Rank history) and details exactly what the response contains: per-day points, category, 7/30-day change, and drop/rise/steady state. It clearly identifies the tool's scope, but never explicitly distinguishes itself from adjacent siblings like get_sku_trend or get_stock_history.

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 concrete use-case phrasing ('is my rank going up or down', 'which products lost rank this week'), which tells the agent when this tool applies. It stops short of naming when-not-to-use or pointing to an alternative sibling, so it does not reach a 5.

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