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

Annotations already cover read-only and open-world safety, but the description adds a genuinely important operational fact absent from structured fields: the call costs $0.05, billed in USDC on Base via x402. That payment prerequisite is the kind of thing an agent must know before invoking. It does not disclose failure behavior, latency, or whether the charge applies to failed calls.

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 that front-loads the resource and scope, then lists outputs and pricing. Every clause carries information; the marketplace and currency enumeration is necessary for disambiguation. Slightly crammed, but nothing is wasted and nothing important is buried.

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 compensates well by enumerating what comes back (ranges, best buy/sell, profit, deals with links), and it discloses the payment requirement. For a 5-parameter tool with full schema coverage this is close to sufficient; it could say more about payment flow or error handling, but an agent can call it correctly as written.

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 every parameter already carries a description and the baseline is 3. The description adds only an indirect hint about fees ("best place to sell after fees"), which maps loosely to ebayFeePercent, and says nothing about how max, condition, or marketplaces shape the result. Adequate but not additive.

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?

Uses a specific verb ("Compare") with a named resource (one product's price) and enumerates the exact outputs: price range per marketplace, cheapest buy, best sell after fees, flip profit and margin, best deals with links. It also names the four marketplaces and the GBP currency, which distinguishes it from the single-marketplace siblings (ebay_market, vinted_search, reverb_search, poshmark_search).

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?

Implied usage is clear: this is the cross-marketplace aggregation tool, while siblings each hit one marketplace. It also documents the default marketplace set (ebay, vinted, reverb) so the agent knows poshmark is opt-in reference data. It stops short of explicitly saying "use ebay_market instead for a single-site search" or warning about when comparison is overkill.

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