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

The annotations already declare read-only, idempotent, and non-destructive behavior, and the description adds substantial behavioral context: no network call, no API key required, no rate limiting, in-process computation, RFC 3021 handling for /31 and /32, and text-format return. This goes well beyond the structured annotations.

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 dense sentences cover behavior, outputs, special cases, constraints, and use case without redundancy. The most important distinction (local, no network call) is front-loaded.

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?

Given the output schema exists, the description does not need to detail return values, and it covers all essential operational context: local computation, authentication/rate-limit status, RFC handling, and intended usage. Nothing critical is missing for calling this tool correctly.

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 input schema has 100% coverage and already explains the cidr parameter with format and example. The description reinforces that the tool computes from CIDR notation but adds little new parameter-level meaning beyond what the schema provides, so the baseline of 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?

The description uses a specific verb ('Compute') with a clear resource ('IPv4 subnet details from CIDR notation') and enumerates the exact outputs. It also distinguishes itself from sibling network tools by emphasizing it is entirely local and purely computational.

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 gives an explicit use case ('Use this for IPv4 address planning') and states what the tool does not do ('It does not query DNS or contact any host'), which implies when not to use it. It doesn't reference a specific sibling alternative, but the local-computation framing is clear enough for an agent to route correctly.

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