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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds the useful 'free to call' cost detail, but discloses nothing about return volume, ordering, or pagination — acceptable but thin for a zero-parameter listing tool.

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 phrase with no filler; the scope (paid services on sale) is front-loaded before the payload (prices, payment terms) and the cost note. It reads as a noun phrase rather than a full sentence, but nothing is wasted.

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?

For a trivial read-only catalog tool with no parameters and no output schema, the description covers what it returns (services, prices, payment terms) and that it is free. It omits return shape and ordering, which is a minor gap given the tool's simplicity.

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 schema has zero parameters, so there is nothing for the description to disambiguate; the baseline for a 0-param tool is 4.

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 verb+resource: a 一覧 (list) of 販売中の有料サービス (paid services currently on sale), plus what each entry contains (価格・支払い条件). It is clearly distinguishable from the buy_* siblings, which perform a purchase rather than a catalog lookup, though it never names those siblings explicitly.

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 only usage signal is '(無料)', indicating the call costs nothing, which implies this is the safe browse-before-you-buy step preceding the buy_* tools. There is no explicit when-to-use statement, no prerequisites, and no named alternative.

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