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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint, covering the safety profile. The description adds behavioral context beyond this: prices are refreshed daily, sorted by 2-year cost, and limited to standard (non-premium) prices. This gives agents useful expectations about data freshness and ordering. It doesn't contradict annotations.

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 two sentences with zero waste. It front-loads the core purpose and immediately provides usage guidance. Every clause contributes to agent understanding, making it exemplary in conciseness.

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 simple read-only tool with one parameter, the description is complete. It states what the tool returns (prices across registrars, refreshed daily, sorted by 2-year cost) and how to use it. With annotations covering safety and no output schema, no critical information is missing.

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 describes the tld parameter with a pattern and example, achieving 100% coverage. The description merely refers to 'one TLD' without adding further syntax or format details beyond what the schema provides. Per the rubric, the baseline of 3 applies when the schema handles the parameter documentation, and the description adds no extra value here.

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 action (compare), the resource (TLD prices), and the scope (one TLD across registrars, non-premium). It explicitly differentiates itself from the sibling check_domain by naming it, so an agent can immediately tell which tool to use for general price inquiries versus specific name checks.

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 explicit usage direction: use for general questions like 'how much is a .io domain' and directs to check_domain for a specific name. This provides both when and when-not to use, along with the alternative tool, leaving no ambiguity.

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