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

Annotations already declare read-only, idempotent, non-destructive, closed-world behavior, and the description adds genuinely new context: validators are all tried, results are ranked with checksum-bearing types above pattern-only ones, matches are structural not proof of type, and the confidence tiers are explained. It also names the response fields and a disclaimer, which is unusually thorough.

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 behavior and usage trigger, then the example, ranking rule, and confidence semantics. It is dense but mostly earns its space; the enumeration of response fields is somewhat redundant given the output schema, which keeps it from being maximally tight.

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 and annotations present, the description nonetheless covers the selection logic, ranking order, confidence meaning, example invocation, and the limitation of structural matching. An agent has everything needed to choose and call the tool correctly.

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 baseline is 3. The description still adds meaning by explaining that country causes national validators to be tried in addition to international ones, and gives a concrete example ('12345678901', 'KW'), which clarifies the scope of the country parameter beyond the schema wording.

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 an exact verb and resource: tries every validator for a country plus international ones and returns the identifier types that accept the value, ranked. The phrase 'Use when a document or form field holds a number of unknown type' cleanly separates it from sibling validate_identifier, which operates on a known type.

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?

Gives a clear triggering condition (unknown identifier type in a document/form field) and implies the alternative of validating a known type. It does not explicitly say 'do not use when the type is already known' or name validate_identifier, so a small inference step remains.

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