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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is covered. The description adds a genuinely useful non-structured fact — it costs 1 credit per call — which lets an agent budget or batch instead of looping. It stops short of noting failure modes (e.g., what happens on an unresolvable or private IP), so it is 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?

One sentence plus a short cost clause, zero filler, and the highest-value information (what you get back) is front-loaded. Every clause carries content.

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?

The tool is simple (one param, output schema present, full annotation coverage) and the description covers purpose, returned data shape at a high level, and cost. What is missing is minor: error behavior for invalid/private IPs and a pointer to bulk_verify for multi-IP lookups.

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?

There is a single required parameter with 100% schema description coverage, so the schema already documents "IPv4 or IPv6 address" fully. The description adds nothing about the parameter — no format examples, no mention of whether private/reserved ranges are accepted — so the baseline 3 applies.

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 ("Look up an IP address") and immediately enumerates the returned data classes (geolocation, connection type, proxy/VPN/Tor/datacenter flags, fraud/risk score), which cleanly separates it from siblings like verify_email and validate_phone. An agent can tell what this does 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?

Usage is only implied by the resource name — an agent infers it should call this when it has an IP to enrich. There is no guidance on when to prefer bulk_verify for multiple IPs, no note on invalid/malformed input handling, and no statement of when this is inappropriate. The credit-cost note is the only usage-relevant signal.

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