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

Annotations already declare readOnly/idempotent/non-destructive/openWorld=false, so the safety profile is covered. The description adds genuinely useful contract detail the annotations lack: the return shape {ok, version, issues} and that version is 4, 6 or null — especially valuable with no output schema.

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 short sentences, front-loaded with the action, then scope, then return contract. Every clause carries information; nothing is 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 single-parameter, no-output-schema validator with full annotation coverage, the description supplies everything an agent needs: purpose, exclusions, and return shape. Nothing required to invoke or interpret 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?

Schema coverage is 100% with one documented param, so baseline is 3. The description's 'literal-address syntax' wording adds meaning beyond the schema by implying no hostnames, ports, or CIDR notation are accepted, tightening the expected input format.

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 specific verb and resource — 'Check IPv4 or IPv6 literal-address syntax' — which is unambiguous and self-distinguishing from the is-*-safe sibling family (each validates a different literal type). An agent can tell exactly what class of input this accepts without opening the schema.

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 usage ('use to screen candidate IP strings') and gives a concrete exclusion ('not test reachability or geolocation'), which prevents a common misuse. It stops short of naming an alternative tool, but no sibling validator competes for this input type.

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