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

Annotations already carry readOnly/idempotent/openWorld/destructive=false, so the 'read-only — does not modify any state or place orders' line is largely redundant. The description does add non-obvious behavioral context: the score>=55 PASS / 35-54 FLAG / <35 BLOCK gate semantics, the caveat that the verdict is an evidence tier rather than a GPV-1 checkout decision, and the disclaimer about marketplace records vs. product quality.

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?

Front-loaded with the core purpose and the scoring rule early, then routing guidance, then caveats. Mostly every sentence earns its place, though the explicit read-only restatement duplicates the annotations and the quality-disclaimer sentence is somewhat 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?

No output schema exists, so the description carries the return-value burden — and it does: score range, full signal breakdown, and verdict tier are all described. Combined with the threshold semantics and scope caveats, an agent has everything needed to call and interpret this tool.

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?

With 100% schema coverage on only 2 params, the schema already documents both `retailer` (with enum) and `product_id` including an ASIN example. The description names the four marketplaces but adds no syntax or format detail beyond the schema, so 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?

States a specific verb and resource ('Return the GoBuy Evidence Score (0-100) and complete signal breakdown for a single retailer listing') and scopes it to four named marketplaces. It actively distinguishes itself from siblings by naming `compare_products` and `analyze_reviews`.

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?

Explicit when-to-use ('individual product lookups') plus two named alternatives with the selecting condition for each (multi-product ranking -> compare_products; requested Amazon review samples -> analyze_reviews). It even states what this tool never does (fetches reviews).

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