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

Goes well beyond the readOnlyHint/openWorldHint annotations by disclosing the billing model (x402, pointer to list_prices), the error-cost behavior ('Not charged for an invalid address'), and the special no-input HTTP path that returns the caller's IP and country. These are exactly the operational facts an agent needs before spending money or relying on a network call.

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?

Three sentences, each front-loaded with the most decision-relevant fact: what it classifies, the no-input behavior, then cost and usage. The long classification enumeration is necessary precision rather than padding.

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 one-optional-parameter, no-output-schema tool, the description covers input semantics, output categories, the special zero-arg mode, and the payment/error model. Nothing an agent needs in order to call it correctly is missing.

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?

The single parameter is fully documented in the schema ('IPv4 or IPv6 address. Omit (HTTP only) to get your own IP.'), which matches the description's restatement of the omission behavior. The description confirms but does not extend schema semantics (e.g., no detail on canonicalization or inputs like CIDR), 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?

Opens with a specific verb plus resource ('Classifies an IPv4 or IPv6 address') and enumerates the exact outputs: family, canonical form, and the full set of classification buckets including IPv4-mapped IPv6. No sibling tool does anything similar, so the agent can select it unambiguously from the list.

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 states the use case ('validating network input and filtering internal addresses') and the zero-arg mode ('With no input over HTTP, returns the caller's own public IP and country'). It doesn't name an alternative or an exclusion case, but no sibling overlaps in function, so there is little to route away to.

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