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

Beyond the readOnlyHint annotation, the description adds genuinely useful behavioral context: the operation is public and requires no API key. It also maps the call to underlying endpoints, clarifying it is a thin passthrough read. It does not discuss rate limits or response shape, hence not a 5.

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?

Two compact sentences, front-loaded with the purpose before the usage hint and endpoint mapping. Every clause carries information: use case, option set, auth requirement, and API mapping.

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 a single optional enum parameter, no output schema, and readOnlyHint already declared, the definition covers what an agent needs: purpose, auth posture, and option semantics. Return shape is not described, but for a flat IP list it is inferable and no output schema exists to demand it.

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% and the enum already enumerates all/ipv4/ipv6, so the description's 'Choose all, ipv4 or ipv6' largely restates schema content. The one addition — that the family selects an address class — is implicit in the enum names themselves, so the baseline 3 is appropriate.

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 verb and resource ('List updown.io's server IP addresses') and immediately scopes it with a concrete use case (firewall allowlisting). It is unmistakably distinct from siblings like updown_list_nodes, which lists monitoring nodes rather than their IPs.

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 supplies a clear triggering context ('e.g. to allowlist the monitors in a firewall') and tells the agent how to select among the family options. There is no explicit when-not guidance or named sibling alternative, which keeps it short of a 5.

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