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

With no annotations provided, the description carries the full burden of behavioral disclosure. It adds a single fact—that no WHOIS or ownership data is involved—which implies a read-only, non-network operation. However, it does not explicitly state that the tool is side-effect-free, that it discards all inputs, or what it returns. The single sentence leaves the agent guessing about output format, error behavior, and whether any data is persisted. This is insufficient for a tool with no annotation safety profile.

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 is a single, compact sentence with zero filler. It front-loads the primary action ('Split a hostname into labels') and adds a relevant exclusion. Every word earns its place, and there is no redundant information. This is an exemplary model of conciseness, though it sacrifices depth for brevity.

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 tool with 9 parameters (even if only 'host' is relevant), no output schema, and no annotations, the description is significantly incomplete. It does not explain what the output looks like (e.g., an array of labels), how to invoke it (which parameter to fill), or when to use it over the numerous sibling tools. The presence of many similar tools (normalize-url, browser-url-ok, etc.) makes this lack of context especially problematic. An agent cannot confidently decide to call this tool without additional information.

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 description coverage is 100%, so every parameter has a clear description in the schema (e.g., 'host' is 'Public hostname'). The tool description adds no parameter-specific meaning—it does not even mention the 'host' parameter by name. Since the schema already documents the parameters, the baseline is 3, and the description does not exceed it. It also does not clarify which parameter is intended for the hostname, though the schema makes that evident.

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 description states a specific verb ('Split') and a clear resource ('a hostname into labels'), and adds the clarifying exclusion 'without WHOIS or ownership data'. It does not degenerate into a tautology, and the core action is unambiguous. However, it does not differentiate from sibling tools like normalize-url or browser-url-ok, which also handle hostnames/URLs, so it lacks the sharpness of a 5.

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 description gives no guidance on when to use this tool versus the many siblings (normalize-url, browser-url-ok, web-fetch, etc.). There is no mention of appropriate contexts, prerequisites, or cases where another tool would be preferred. The only hint is the 'without WHOIS' phrase, but it does not state when one should choose this over a URL normalizer or fetch tool.

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