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

With no annotations, the description does carry the behavioral burden and it does disclose two real traits: the $0.0029 cost and the implementation backend (Rust WASM). It does not state what the validation returns on failure, whether it reports the specific failing condition, or how malformed input is handled.

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 short sentences with no filler; the validation mechanics are front-loaded after the price. Leading with the price rather than the action is slightly awkward for scanning, but nothing is wasted.

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 pure validator with no output schema, the description covers input format, algorithm, and cost — enough to call it correctly. The remaining gap is the absence of any statement about the return shape (e.g. valid/invalid plus reason), which matters since there is no output schema to fall back on.

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 coverage is 100% for the single 'lei' parameter, whose schema description already gives the 20-character format and an example. The description's format note merely restates the schema, so 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 (Validate) and resource (LEI, ISO 17442) and pins down the exact checks performed (20-char alphanumeric format, Mod 97-10 check character). It is distinguishable from siblings like iban_check and luhn_check by the standard it cites, though it never names the closest sibling, mod97_check, which performs the underlying algorithm.

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 implied by the domain: validate an LEI string. There is no explicit when-to-use/when-not, and no routing to mod97_check or sanctions_check/onchain_address_check despite those being adjacent validators. The price disclosure ('Paid ($0.0029)') is useful for cost-aware selection but 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.