validate_isin

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

With no annotations, the description discloses that it checks format, Luhn digit, and returns country code. This provides useful behavioral traits beyond the input schema, though it could mention whether it makes external calls or if it's purely local.

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 sentences, front-loaded with imperative 'USE THIS', no fluff. Every sentence adds value: motivation, action, and trigger condition.

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?

Given a simple validation tool with one parameter and no output schema, the description covers all necessary aspects: purpose, input constraints, checks performed, and output. No gaps.

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% (single parameter with description and example). The description adds no extra meaning for the parameter itself; it only elaborates on output behavior. Baseline 3 is appropriate as schema already carries the burden.

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?

Clearly states the tool verifies ISIN identifiers, checking format and Luhn check digit, and returning country code. The verb 'verify' and resource 'ISIN' are specific, and the tool is distinct from siblings by name and description.

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?

Explicitly says to call when a user supplies a security/instrument identifier and warns against assuming validity. While it doesn't name alternatives, the context suggests using this for ISIN specifically; missing explicit when-not-to-use but overall clear.

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