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

The description implies a non-destructive operation (splitting a hostname) but does not explicitly state that the tool is read-only or free of side effects. It also does not clarify the behavior of the extra parameters (e.g., 'ref', 'url') which are marked as 'discarded' in schema but not mentioned in the description.

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 concise, consisting of a single sentence, which is efficient. However, it lacks any structural elements like sections or bullet points to separate purpose, input, output, or caveats, making it appear underdeveloped for a tool with multiple parameters.

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?

Given the tool has nine parameters and no output schema, the description is severely incomplete. It does not mention the expected return value, output format, or provide any examples or edge-case handling. This leaves the agent without enough context to invoke the tool correctly or interpret results.

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?

The description mentions 'hostname' but does not map it to any specific parameter such as 'host'. It does not explain the purpose or relevance of the other eight parameters, nor does it clarify which ones are actually used versus ignored, leaving the agent to rely solely on schema descriptions that may be confusing.

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 clearly states the tool's core function: splitting a hostname into labels, and it explicitly excludes WHOIS or ownership data, which helps set expectations. However, it does not explicitly name the 'host' parameter as the input, which could cause slight ambiguity.

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 provides no guidance on when to use this tool versus alternatives like 'normalize-url' or 'fetch-status'. It lacks information about typical use cases, required input format, or any conditions that would make this tool preferred over others.

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