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

Annotations already declare readOnly/idempotent/openWorld/non-destructive, but the description adds substantial behavioral context beyond them: no storage or logging, no firewall rules changed, VPN/proxy alters the observed path, one call observes one address family only, Cloudflare Worker subrequest address semantics, and the result is not an identity proof. These are the kinds of caveats that prevent misuse.

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?

Purpose is front-loaded in the first sentence, and each subsequent sentence carries a distinct caveat. It runs long (seven-plus sentences) and could be tightened, but there is no filler or repetition.

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 no-parameter read tool with rich annotations and an output schema, the description covers everything an agent needs: what is observed, whose address it is, what changes the result (VPN/proxy), and what it does not reveal. Return-value explanation is unnecessary given the output schema, and none 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?

The tool takes zero parameters, so the baseline is 4. The description confirms the empty-object input ('Takes an empty object') and names the return fields (ip and family), which is mild reinforcement rather than new parameter meaning.

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: inspect the public IPv4/IPv6 address observed for the connection making the call. This is unambiguous and clearly distinct from the CIDR-manipulation siblings (cidr-cover, cidr-subtract, range-to-cidrs). An agent can identify exactly what the tool returns without opening the schema.

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?

Explicitly states when NOT to use it ('If the user needs their browser or computer connection, direct them to the web tool or a CLI running on that machine') and scopes it to the MCP client connection. It also excludes near-miss expectations (private addresses, pre-proxy address, both families), so the agent knows what this call cannot satisfy.

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