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

Annotations already establish readOnly, non-destructive, open-world behavior, so the description correctly spends its words elsewhere: the authoritative source (GLEIF global register) and the returned data set. It does not disclose failure behavior (e.g. what happens for an unregistered or malformed LEI), which is the main remaining gap.

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?

Three sentences, each doing distinct work: what it looks up, what it returns, when to use it. The return-field enumeration is front-loaded usefully since no output schema exists, and nothing is redundant.

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 one-parameter lookup with no output schema, the description compensates well by listing the returned fields and naming the register. It is nearly complete; only error/not-found behavior and data freshness are unstated.

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?

With a single parameter at 100% schema coverage (min/max length 20, example value), the schema already carries the semantics. The description adds only the ISO 17442 framing and 'alphanumeric' context, which is marginal value beyond the structured field.

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 (look up) and resource (LEI in the GLEIF global register), plus the required key format (20-character ISO 17442 code). This implicitly separates it from name-based siblings like lei_search and lei_relationships, but it never names those siblings explicitly, so it stops short of a 5.

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?

"Use to validate or enrich a counterparty that publishes an LEI" gives a clear, actionable context for selecting this tool. It offers no exclusions or explicit pointer to alternatives (e.g. use lei_search when you only have a name), which keeps it below a 5.

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