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

Annotations already declare a safe read (readOnly, idempotent, non-destructive, closed-world), and the description goes well beyond that: it defines the return shape, the equal-endpoint and full-address-space edge cases, error attribution to start/end, the no-silent-swap guarantee, and the local-vs-remote execution distinction. None of this is recoverable from the 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?

It is front-loaded with the purpose before inputs, outputs, edge cases, and non-goals, and virtually every clause carries information. The single dense block is longer than strictly necessary, and a few items (64-char cap, whitespace handling) duplicate the schema, keeping it from a 5.

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 transformation tool with edge cases and a non-trivial contract, the description covers input validation, boundary behavior (equal endpoints, /0), error reporting, deterministic ordering, and explicit non-goals. With an output schema present it does not need to explain returns, yet its added contract details make the definition fully sufficient.

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 description coverage is 100%, so the baseline is 3, but the description adds real constraints beyond the schema: same address family, no CIDR prefixes, and end at or after start. It restates the 64-character cap and non-swapping behavior rather than adding to them, but the family/prefix rules genuinely help the agent construct valid input.

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 states a specific verb and resource: produce an exact CIDR allowlist from one inclusive start/end IP range. The operation direction (range -> CIDR list) is unambiguous and effectively opposite to siblings like cidr-cover/cidr-subtract, but no sibling is named, so the differentiation is implicit rather than explicit.

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?

It opens with 'Use to prepare an exact CIDR allowlist from...', which gives clear context for when the tool applies, and the closing 'This does not...' clause rules out adjacent tasks (live usage inspection, firewall modification, ACL export). It never names an alternative tool or the condition that would select one, so it stops short of full when/when-not routing.

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