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

Annotations already cover the safety profile (readOnlyHint=true), and the description adds genuine context: checksum-only semantics, no business-status verification, and free of charge. It stops short of describing the return shape (e.g. what is returned on checksum failure), which is the one remaining behavioral gap.

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 short sentences, front-loaded with the core action and format, followed by the important caveat. No filler or restatement of the title.

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 validator with no output schema, the description covers what it validates, what it returns formatted, and the key limitation. The only missing piece is failure behavior / exact return value, which an agent would have to discover by calling.

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 0% (a bare untyped string), so the description carries the load — and it does, defining the identifier, its 10-digit length, and its canonical hyphenated form. It could be slightly clearer about whether input should be digits-only or may include hyphens, but '10 digits' resolves most of that ambiguity.

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 precise verb and resource — validate a South Korean business registration number (사업자등록번호, 10 digits) — and specifies the output formatting (XXX-XX-XXXXX). Nothing overlaps with the romanization/cleanup siblings, so an agent can route to it unambiguously.

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 scopes the tool: 'Checksum only; does not confirm the business is active,' which tells the agent when the result is insufficient for a due-diligence use case. It does not name an alternative tool or state prerequisites, but the siblings are unrelated functions so there is little to disambiguate.

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