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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), yet the description still adds real value: what the return contains (first-year and renewal price in NOK incl. 25% VAT), the failure behavior (reason given if the extension is not sold), and an output-handling rule (always show buy_url). It stops short of describing latency or rate limits.

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?

Front-loaded with the core action and price scope, followed by a single actionable instruction about buy_url. Dense but every clause carries information; slightly long-running first sentence is the only cost.

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?

With no output schema, the description compensates by describing the shape of the result — availability, yearly prices with VAT basis, failure reason, and buy_url. An agent has everything needed to call the tool and present results correctly.

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 coverage is 100% and the schema itself documents the bare-name default (example -> example.no) and Unicode handling. The description adds nothing about the parameter, so baseline 3 applies.

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?

States a specific verb and resource — check availability and price for one domain — and names the provider (pekt) plus units (NOK/year incl. VAT). It is clearly distinguishable from siblings like list_extensions and suggest_domains, which cover different lookup scopes.

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?

"Check whether one domain name is available" scopes usage to a single-domain lookup and implicitly contrasts with the sibling list/suggest tools. However, it never explicitly names an alternative or states when not to use it.

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