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

Annotations already establish the safe-read profile (readOnly, idempotent, non-destructive, closed-world), so the description is free to add the behavioral layers that matter: results are serialized as decimal strings, IPv4 results include mask and usable-host bounds with special /31 and /32 handling, and returned evidence is flagged as untrusted data rather than instructions. That last point is a genuinely useful injection-safety disclosure absent from the annotations, though the exact response shape remains unspecified.

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 what is computed before the format and safety notes. Every sentence carries distinct information — scope, output encoding, IPv4 edge-case behavior, and trust posture — with no filler.

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 return-value context, and it does: decimal-string serialization, mask and usable-host bounds for IPv4, and explicit /31 and /32 handling. It stops short of enumerating the actual fields an IPv6 response contains, which is the one remaining gap for a parser tool.

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?

There is a single parameter and the schema already documents it fully (100% coverage) with a concrete IPv4 and IPv6 example. The description adds nothing about the cidr argument itself, so the baseline 3 for schema-driven parameters is correct.

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 ('Calculate IPv4/IPv6 CIDR boundaries and exact address counts') and scopes it to a single CIDR input, which implicitly distinguishes it from check_cidr_overlap and plan_subnets. It never names those siblings, so the differentiation relies on inference rather than explicit contrast.

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?

Usage is only implied: an agent can infer this is the tool for deriving boundary/count facts about one CIDR, but there is no when-to-use statement, no prerequisites, and no mention of when to prefer check_cidr_overlap or plan_subnets instead.

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