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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so safety is covered. The description adds genuinely new behavioral context beyond the annotations: a cost model (free within a daily allowance, then $0.003 USDC per call via x402), which matters for call planning. It still doesn't say how an unknown or invalid LEI behaves (empty result vs error) or whether results paginate.

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 no filler, and the subject (what the tool returns) is front-loaded. The pricing sentence is longer than the functional sentence, but it carries real information rather than padding.

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?

An output schema exists, so return-value explanation is not required, and with one fully documented parameter this is a simple tool. It is close to complete; the only unresolved agent questions are error behavior for an unknown LEI and the mechanics of the x402 payment path.

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?

Schema description coverage is 100%, so the single 'lei' parameter is already documented, and the description implicitly confirms the entity is identified by its LEI. It adds no format, validation, or normalization detail beyond what the schema provides, so the baseline 3 is appropriate.

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 the resource (ISINs) and the relationship (issued by an entity), so an agent can tell it returns securities identifiers tied to a given entity. It lacks an explicit retrieval verb and does not distinguish itself from siblings such as gleif__by-isin, which performs the inverse ISIN-to-entity 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?

No when-to-use guidance is given: nothing says to use this when you have an LEI and need its issued securities, and no alternative is named (gleif__by-isin is the obvious inverse). The only contextual sentence is about pricing, which is not usage guidance.

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