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

Annotations already declare readOnlyHint=true, openWorldHint=false, and destructiveHint=false, so the safety profile is covered structurally. The description still adds genuinely useful behavioral context by stating no payment is incurred and no provider call is made, which is exactly the kind of cost/side-effect information annotations cannot express.

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?

A single compact sentence with no filler, and the read-only qualifier is front-loaded. It is arguably over-terse given the absence of any statement about what discovery yields, but every clause present earns its place.

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 and no parameters, the description is the only place an agent could learn what this discovery step produces, and it never says. Annotations cover the safety profile, but the return content and the relationship to the invoke_/prepare_/result_ siblings go unexplained.

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?

The tool takes zero parameters and the schema is empty, so there is nothing for the description to disambiguate. Per the baseline for parameterless tools, a 4 is appropriate; no parameter information is missing.

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 core clause 'Read-only discovery for product_detail_v0' largely restates the tool name, but the qualifier 'no payment or provider call' distinguishes it from the invoke_product_detail_v0 sibling by signaling a metadata/spec lookup rather than an actual product fetch. The description never states what 'discovery' actually returns, so the purpose remains only partially resolved.

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?

There is no explicit when-to-use or when-not-to-use statement. The 'no payment or provider call' clause implies this is the safe preview path before invoke_product_detail_v0, but the agent must infer that routing decision rather than being told.

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