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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds two useful behavioral facts beyond them: results are ordered best-first, and condition only affects eBay categories. It does not describe what a result row contains (product, price, seller) or how the per-unit computation behaves when unit data is missing.

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?

Three compact sentences with no filler, and the core ranking behavior plus unit basis is front-loaded. The opening 'Cheapest price per unit, best first:' reads slightly awkwardly, but 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?

With no output schema, the description is the only place to learn what comes back, and it stops at 'cheapest price per unit, best first' without describing result fields or ordering ties. Combined with the unexplained limit parameter, the definition is workable but leaves gaps an agent would have to discover by calling it.

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 0%, so the description must carry parameter meaning. It does well for category (key from list_categories plus labeled examples) and condition (allowed values, eBay-only scope, defaulting to any), but the limit parameter's meaning and cap of 25 are never mentioned, leaving one of three parameters undocumented anywhere.

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 names a specific operation: ranking items by cheapest price per unit, with the unit basis spelled out per category type (per GB, per battery, per ounce, per foot). This is clearly distinct from get_price or search_prices in intent, though it never explicitly names those siblings to differentiate.

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?

It tells the agent where category keys come from ('a key from list_categories') and when condition applies ('for eBay categories'), which is genuine routing guidance. It gives no guidance on when to prefer this over search_prices, deals, or used_vs_new, so the choice among siblings is left to inference.

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