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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint, so the safety profile is covered. The description usefully adds the validation algorithm (structure plus Luhn mod-10 over A=10…Z=35), which tells the agent that a plausible-looking ISIN with a bad check digit will fail, but it says nothing about failure semantics (error vs. negative result) or output shape.

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?

A single front-loaded sentence with no filler; the scope, standard, and algorithm come first and 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?

With an output schema, full annotation coverage, and a fully documented single parameter, the description carries only the burden of stating the validation rule, which it does. The one remaining gap is not indicating how a failed check is surfaced, but the output schema likely covers that.

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%, with the schema already spelling out the 12-character layout and the spaces-allowed rule. The description adds no parameter detail beyond the A=10…Z=35 conversion, 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 ('an ISIN (ISO 6166)'), plus the exact method used, which cleanly separates it from siblings like sedol_check, lei_check, and ean13_check. An agent can identify the tool's function without opening the schema.

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 says what is checked but never when to reach for this tool versus alternatives such as batch_validate (bulk validation) or the other identifier checks. No exclusions, prerequisites, or routing guidance are given.

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