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

Annotations already cover read-only and open-world nature, but the description adds genuinely useful behavioral context beyond them: the cost ($0.005 USDC per call via x402 or prepaid credits), the free-trial eligibility, the 'companies only' scope limitation, and what the LEI mode returns (direct and ultimate parents). Does not explain the non-idempotent hint.

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?

Front-loaded with the core purpose and lookup modes, then a short pricing sentence. Dense but nearly every clause earns its place; minor redundancy between the register name and lookup modes.

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 an output schema present, return values need not be explained. The description covers scope, modes, pricing and trial status, leaving an agent able to call it correctly; the only omission is guidance relative to sibling lookups.

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 schema already documents all four parameters. The description reinforces the LEI-parent behavior and the national-number usage but adds no syntax or format detail beyond what the schema provides; baseline 3 applies.

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 (legal entities in the global LEI/GLEIF register), and enumerates the three distinct lookup modes (by LEI, by name, by national company number). This is clearly distinguishable from siblings like company-profile, company-report, eu-vat and eu-fx.

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 description implies usage by mapping each input to a search mode, but never states when to prefer this tool over related siblings (e.g. company-profile, company-report) or any when-not conditions. Usage is inferable but not explicitly guided.

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