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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description still adds real value beyond them: no network access, no stored state, determinism, and concrete limits (64 KB input, 1 s per call, 1 MB result, 1,000 blocks max) that an agent needs to size inputs and avoid failures.

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?

The core sentence is front-loaded and tight, but the description is duplicated wholesale in Spanish and English and the 'When' clause is boilerplate that does not belong to this tool, padding the definition without adding selecting information.

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 an output schema present, the description does not need to explain return values, and it compensates by stating determinism, the block-count cap and the input/time/size limits. The main remaining gap is the vague applicability list and the unmentioned cidr-split relationship.

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 only two well-named parameters, so the schema does the heavy lifting. The description adds the useful fact that both IPv4 and IPv6 are accepted and that the range is inclusive, but it does not clarify edge cases such as start greater than end or mixed-family input, so it stays at the baseline.

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 opening sentence gives a specific verb and resource: it converts an inclusive start-end IP range into the minimal covering list of CIDR blocks, capped at 1,000. That is precise enough to distinguish it from the CIDR-oriented siblings, and the description names cidr-contains explicitly as the thing it is not.

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 'Not for' clause is genuinely useful and names the alternative (cidr-contains) with the condition that selects it. But the positive 'When' clause is a generic template list (URLs, tokens, versions, HTML/Markdown documents) that does not actually describe when to build a CIDR range, and it never mentions cidr-split, which is the closest-looking sibling for block decomposition.

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