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

Annotations already declare readOnlyHint and openWorldHint, and the description adds genuinely new behavior: it returns a formatted/normalized number plus carrier and line-type analysis, and it discloses a per-call cost of 40 points. Missing is what happens on an invalid number (error vs. negative result), which would complete the picture.

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 and short, with the useful cost tag at the end. The Korean sentence largely restates the English one, which is redundant for an agent, though it may be an intentional localization choice.

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 no output schema, the description must carry the return contract, and it only names three of the outputs without structure or error behavior. Adequate for a single-parameter lookup, but the return semantics remain underspecified.

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% and the single parameter's format (domestic 010..., overseas +country code) is already documented in the schema. The description adds no syntax or constraint beyond that, so the 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 specific verbs (validate, format) plus the resource (phone number) and the extra outputs (carrier, line type), so the agent knows exactly what it gets. It is implicitly distinct from check_email_valid and check_spam_number by resource, but it never names a sibling to sharpen the boundary.

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 the tool does but never states when to choose it over alternatives or any prerequisites. No guidance on when-not to use it, or how it relates to check_spam_number, which also concerns phone numbers.

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