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

Annotations already declare the safety profile (readOnlyHint, idempotentHint, non-destructive), so the bar is lower and credit goes to added context. The description discloses what the call returns (matching prefix, source, crawlers), the meaningful semantic that a miss is 'reported as a miss, not as a forgery', a six-hour data refresh window, and that the MCP call wraps the same implementation as a public HTTP endpoint.

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?

The description squanders its front-loaded position on a full inline JSON-RPC payload for a different tool (whoami) before stating what this tool does. The remaining content is reasonably tight and informative, but the whoami invocation should have been a one-line hint rather than a verbatim call payload.

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 single-required-parameter, read-only check tool with no output schema, the description covers purpose, return semantics, miss handling, data freshness, a worked example, and an alternate invocation path. Nothing an agent needs to call it correctly is missing; only minor extras like rate limits or malformed-IP handling are absent.

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 schema already documents ip as 'IPv4 or IPv6 address to check'. The description adds only a concrete example value (20.171.206.5) and reaffirms IPv4/IPv6 support already present in the schema, so the baseline 3 for full schema coverage 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?

The operative sentence 'Test an IPv4 or IPv6 address against every crawler prefix the operators themselves publish' is a specific verb+resource statement that clearly distinguishes this from siblings like lookup_crawler and list_crawlers. However, the description opens with an instruction to call whoami, a different tool, so the very first content an agent reads is not about this tool's own purpose.

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 only usage guidance is a workflow hint ('FIRST CALL, needs nothing' → call whoami), a concrete example parameter value, and an alternative HTTP transport. There is no explicit statement of when to use this tool versus the sibling lookup/classification tools, and no when-not-to-use or exclusion criteria.

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