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

With no annotations, the description carries the full burden. It only says WHOIS/ownership data is absent; it doesn't disclose invalid-hostname behavior, side effects, discarded inputs, or return shape. Schema hints that some fields are 'discarded' are not in the description and cannot compensate.

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 tight sentence, front-loaded with the action and the key exclusion, with no filler. It is concise but at the cost of completeness, so it earns a 4 rather than a 5.

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 an 8-parameter tool with no annotations and no output schema, one sentence is insufficient: required vs optional fields, output format, failure behavior, and positioning among sibling tools are all missing. The 'host' parameter in the schema is the only clue to how to invoke it.

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 schema documents all properties, so the baseline is 3, but the description adds no parameter guidance and the schema mixes unrelated fields (city, feed, json, path, and a root-level 'Name of a file to delete' description) that don't fit a hostname-splitting tool. An agent has no explicit pointer that 'host' is the relevant input.

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 concrete action ('Split a hostname into labels') and a clear boundary ('without WHOIS or ownership data'), which distinguishes it from enrichment/ownership tools. It doesn't define the output shape or mention any siblings, but the core purpose is unambiguous.

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?

Usage context is implied: this is for syntactic hostname splitting, not for WHOIS or ownership lookup. It gives no explicit when-to-use/when-not-to-use comparison with sibling tools such as normalize-url or fetch-status, so the agent must infer the boundary.

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