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

Annotations already declare readOnlyHint and openWorldHint, but the description adds genuinely new behavioral facts: a $0.002 USDC charge per successful call, x402 payment across Base/Solana/Arc, and that failed calls are free. That cost-and-payment disclosure is exactly the kind of context annotations cannot carry. It omits any note on result limits or pagination, keeping it from a 5.

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?

Purpose and market scope are front-loaded in the first clause, and the billing sentence is a compact, self-contained unit. The long enumerated field list (price, shops, category, popularity rank, rating, price-drop, condition, stock, image, URL) is somewhat over-stuffed for a tool that has an output schema, costing it a point on tightness.

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 only two parameters, full schema coverage, an output schema, and clear read-only annotations, the definition covers what an agent needs: what it searches, which markets, and what it costs. The return-field enumeration is redundant given the output schema but not harmful, and no critical calling information 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 description coverage is 100%, with 'q' and 'market' fully documented including the uk/se/dk values, so the schema already does the work. The description restates the three markets but adds no query syntax, matching behavior, or defaulting detail beyond what is structured. 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?

Names a specific verb and resource ('Price comparison from PriceRunner (Klarna)') and pins the exact geography covered (UK, Sweden, Denmark), which cleanly separates it from the fifty-plus single-retailer siblings like ecommerce_amazon_bestsellers or ecommerce_target_reviews. An agent knows immediately this is a cross-shop aggregator for three Nordic/UK markets.

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 description gives clear contextual signals for selection – multi-shop price comparison, limited to uk/se/dk markets, and priced per call – which lets an agent decide between this and a single-retailer sibling. It stops short of naming an explicit alternative or a when-not condition, so it does not reach the top band.

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