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

Annotations already establish readOnly, idempotent, non-destructive and closed-world behaviour, so the bar is lower, and the description still adds real context: prices are in EUR, derived from sold (not asking) prices, aggregated over 30/90-day windows and optionally pooled across markets. It does not say what happens for models with no sales data, but the output schema covers the response shape.

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?

One dense sentence with the outcome front-loaded followed by statistics, unit, windows and market scope. Every clause carries information; nothing is padded.

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 rich annotations, a complete input schema and an output schema, the description needs only to convey what the number means and its scope, which it does exactly. Nothing required to call the tool 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%, with both model and country fully documented in the schema itself. The description only reinforces the pooling semantics of omitting country and adds no format or syntax detail beyond that, so the schema is doing the heavy lifting and 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?

The description states a precise verb and resource: 'what a used PC part actually sells for on eBay', then names the exact statistics returned (sold-price median, p25-p75) and their windows (30 and 90 days). This is plainly distinguishable from check_ebay_listing (a single listing) and list_tracked_models (the catalogue), so an agent can select it 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?

The phrase 'for one market or all seven pooled' hints at the choice an agent makes via the country parameter, but it never says when to prefer this tool over check_ebay_listing or when to pool versus filter. Usage is implied rather than explicitly guided.

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