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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds the useful behavioral nuance that results are the primary rather than secondary/illiquid listing, but says nothing about the return shape, error behavior when no primary listing exists, or data freshness.

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 zero waste; the core action is front-loaded and the rationale follows immediately.

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 single-parameter lookup with no output schema, the description leaves the return value and no-match behavior unexplained, and does not differentiate from the closely related general_isin sibling. It is adequate but not complete.

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?

Only one parameter, and schema description coverage is 100% ('isin'), so the schema already carries the parameter burden. The description adds no format or validation detail (e.g., ISIN format, case sensitivity) beyond 'for a given ISIN'.

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 ('Find the primary listing for a given ISIN'), so an agent can tell what the tool returns. It does not, however, distinguish itself from the sibling general_isin, which also keys off an ISIN and could plausibly be confused with this lookup.

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 second sentence ('Useful to avoid secondary or illiquid listings') implies when the tool is valuable, but there is no explicit when-to-use/when-not guidance and no named alternative (e.g., general_isin) for the cases this tool does not cover.

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