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

Annotations declare readOnlyHint=false, which would normally mislead for a pure computation; the description explicitly reconciles this ("Reads or computes only; not marked read-only because each call is charged"). It also discloses the payment/auth path (x402 USDC, card key via /credits) and that failed calls are free — real behavioral context beyond 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?

The core purpose and enumerated outputs are front-loaded, followed by usage, example, and billing. Every clause carries information, though the pricing sentence is dense; nothing is wasted but the block is packed.

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 compensates by enumerating all returned fields (network/broadcast, host range, netmask, count, membership boolean). Billing and the annotation reconciliation round it out; nothing an agent needs to call it is missing.

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%, so the schema already documents both parameters; the baseline of 3 is lifted by the concrete example "cidr=192.168.1.0/24, ip=192.168.1.77", which shows expected formats and that ip is combined with cidr.

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 resource (IPv4 network in CIDR notation) and enumerates exactly what it produces: network/broadcast address, first/last usable host, netmask, address count, and IP-membership. This scope is clearly distinct from the sibling ip_info, which looks up a host rather than doing network math, even though it isn't named explicitly.

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?

"Use for firewall rules and allowlists" gives clear domain context for when the tool applies, plus a worked example. It stops short of naming alternatives (e.g. ip_info) or stating when-not to use it, so no exclusions are offered.

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