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

Annotations only declare readOnlyHint and openWorldHint; the description adds material context those do not cover: a $0.002 USDC charge per successful call, settled via x402 on Base/Solana/Arc, with failed calls not billed. That billing/attempt semantics is exactly the kind of behavior an agent needs before invoking a metered tool. It stops short of stating rate limits, wallet/auth requirements for payment, or latency.

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 sentences, no filler: the first front-loads what the tool returns, the second front-loads cost and payment semantics. The return-field enumeration is dense but earns its place for a discovery tool. Slight verbosity in listing every returned field when an output schema already exists.

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 an output schema present, the description does not need to explain return shapes, and it covers the one thing structured fields cannot: that this is a paid, x402-metered call charged only on success. Together with the read-only/open-world annotations, an agent has everything needed to call it 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?

Single required parameter with 100% schema description coverage, so the schema already carries the semantics (IPv4 format, example 8.8.8.8, required). The description only restates 'for an IPv4 address' and adds no format constraints, validation notes, or examples beyond the schema — 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 ('Censys host view for an IPv4 address') and enumerates the returned data: services, ports, protocols, last scan time, software, AS, location, network owner, reverse DNS. Naming Censys as the data source implicitly distinguishes it from sibling host/geo lookups such as security_shodan_host_summary and security_ip_geolocation_asn.

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 case is implied (look up a host by IPv4 to see exposed services and network context), and the stated price gives an agent a reason to prefer a cheaper alternative. However, it never says when to choose this over security_shodan_host_summary or security_open_port_scanner, and offers no exclusions or prerequisites.

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