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

Annotations only declare readOnlyHint, so the description carries real weight, and it does disclose a non-obvious behavioral trait: the response is large and costs 100 tokens. That cost warning is genuinely useful for planning. It stops short of saying whether the list is paginated or what fields each row contains.

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?

Two short sentences with the cost warning front-loaded after the scope statement. The full Japanese restatement roughly doubles the length for no new information in a single-language context, which is mild waste but not obstructive.

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 can learn what comes back, and it only says 'full list.' It does not state the fields per row (code, name, product type) or whether the token cost scales, leaving a real gap for a list tool whose output feeds other calls.

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, so there is nothing for the description to disambiguate and the baseline applies. The product-type mention (014/023) is useful framing of what the fixed result set contains rather than a parameter constraint.

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 ('Full list of covered Japanese ETFs / ETNs') and narrows scope with product type codes 014/023. This is distinguishable from siblings like get_etf_metrics (per-ETF data) and list_stocks (equities) without opening any schema.

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?

Usage is only implied: an agent infers this is the entry point for discovering the ETF universe before calling get_etf_metrics. There is no explicit when-to-use, no 'use this instead of X' routing, and no statement about whether the ETF metrics tool requires an identifier from this list.

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