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

Goes well beyond the readOnly/destructive annotations by disclosing that private and reserved addresses are refused with HTTP 400 and are uncharged, that pricing is $0.01/call via x402 USDC or card key with the first 25 free, that failed calls are free, and why repeats are not free (each call is charged) — which explains the idempotentHint=false. This is exactly the kind of cost and failure-mode context an agent needs before calling.

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?

Front-loads purpose and returned fields, then constraints, then an example, then pricing — a sensible order with no filler sentences. The pricing/billing sentence is dense and long, but each clause carries information an agent needs (cost, free tier, failure charging).

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?

There is no output schema, and the description compensates by enumerating the response fields. Combined with failure behavior (400 for private/reserved), billing semantics, and an example, an agent has everything needed to decide to call and to invoke 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 coverage is 100% and the single parameter is already described as 'Public IPv4 or IPv6 address', so the baseline is 3. The description adds value with a concrete example (ip=8.8.8.8) and the functional constraint that private/reserved space is rejected, telling the agent what values are valid beyond the schema's wording.

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 (look up) and resource (IPv4/IPv6 address holder) and enumerates the returned fields: holding organisation, network name and range, allocation type, registration country, abuse contact, registry. It also distinguishes itself from geolocation tools with 'Registration country, not city geolocation', so an agent can tell it apart from siblings like ip_info.

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?

Gives a concrete use case ('see which company or ISP a log or firewall address belongs to') and an explicit exclusion ('Registration country, not city geolocation'), which implicitly routes geolocation queries elsewhere. It does not name the sibling tool (ip_info) directly, so it stops short of the strongest routing guidance.

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