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

With no annotations provided, the description carries the behavioral burden. It usefully discloses that the extraction works 'offline', which is a meaningful behavioral trait. It does not mention edge cases such as invalid URLs, IP addresses, or IDN/punycode handling, but for a simple transform this is a moderate gap.

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, concise sentence that front-loads the core action and resource. Every word earns its place, aside from the minor redundancy of 'Registered Domain:' before the action, which is acceptable.

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?

This is a low-complexity tool with one parameter and an output schema, so the description does not need to detail return values. The main gap is the lack of explicit usage guidance and parameter format clarification, but the core behavior is sufficiently clear for an agent to attempt a call.

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 input schema has one parameter, q, with no description at all (0% coverage). The description's phrase 'from URL' suggests that q is a URL, which adds some meaning, but it does not clarify expected format, default behavior, or what happens with an empty q.

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 action and resource: 'Extract eTLD+1 registered domain from URL'. This clearly identifies the tool's purpose and distinguishes it from sibling tools like hostname or urlparse, though it does not explicitly name those alternatives.

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 is implied: if an agent needs the registered domain portion of a URL, this tool is appropriate. However, there is no explicit guidance on when not to use it or which sibling tools to choose instead, leaving some ambiguity.

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