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

Annotations cover safety/open-world posture but leave behavior vague (readOnlyHint=false on a search tool is unexplained). The description fills that gap usefully: it discloses that saved offers persist after a failed refresh with stale flags and source timestamps, that results carry citations, coverage and pagination, and that Cloudflare samples are explicitly labeled. That is real behavioral context beyond the structured fields.

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?

Four sentences, front-loaded with the core compare action before the staleness and return-value details. Dense but no filler; the scoping exclusion is placed last, which is slightly buried but 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?

For a 17-parameter search tool with no output schema, the description covers return shape (prices, citations, timestamps, coverage, pagination), default ordering, and stale-data behavior. Since the schema fully documents parameters, the remaining burden is small; a little more on when to prefer this over sibling price tools would make it complete.

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 the schema already documents all 17 parameters in detail, making 3 the baseline. The description adds only the default sort context ('annual renewal by default') and the labeling of Cloudflare samples, contributing little beyond what the schema provides.

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+resource: compare standard renewal prices across domain extensions and registrar offers, sorted by annual renewal. It also carves out scope with 'Does not check exact-name availability,' which separates it from the check_availability siblings. It stops short of distinguishing itself from price-adjacent siblings like get_tld_prices or estimate_cost, so it lands at 4 rather than 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?

Usage context is implied ('Find affordable domain extensions and registrar offers') and one exclusion is given ('Does not check exact-name availability'). However, no alternative tool is named and no explicit when-to-prefer rule is stated, so the agent must infer routing from sibling names alone.

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