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

Annotations already declare readOnly, idempotent, non-destructive, closed-world, so the safety profile is covered. The description adds genuinely new context: a 4,096-per-call cap, that a total count is returned, and that payment of $0.003 USDC via x402 on eip155:8453 is required — a material operational detail no structured field conveys.

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 compact sentences, front-loaded with the core action, then scale/response, then cost. No filler; the pricing sentence is dense but necessary.

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?

No output schema exists, and the description compensates by mentioning the subnet list plus total count and the per-call cap. Combined with annotations and the paywall note, an agent has nearly everything needed to call it 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?

Schema description coverage is 0%, so the description must compensate. It explains cidr and newPrefix indirectly ('subnets of a given prefix length inside a parent block') and the limit cap ('up to 4,096 per call'), but omits the default limit of 256 and the valid prefix range, leaving partial gaps.

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?

Specific verb+resource: 'Split a CIDR block into smaller subnets', reinforced by a concrete example (/16 into /24s). It does not explicitly distinguish itself from cidr_aggregate or cidr_info, though the split semantics are inherently distinct from aggregation.

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 example clarifies the intended operation, but there is no explicit statement of when to use this versus cidr_aggregate (the inverse) or cidr_info, nor any note about prerequisites such as newPrefix needing to be longer than the parent prefix.

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