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

Annotations already declare the safe read-only, idempotent, open-world profile, so the description's job is to add context — and it does: it discloses that prices are in NOK and include 25% VAT, that the payload includes registry notices, and that ownership eligibility varies by extension (.eu requires an EU/EEA holder, .se/.nu require an ID number). That is genuinely useful behavioral/domain context beyond the 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?

One compact sentence that front-loads the core purpose ('what buying one extension at pekt involves') and then enumerates the returned fields. The nested parentheses are readable and every clause carries information, though the sentence is dense enough that a second short sentence about when to prefer it over siblings could have been added without bloat.

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 single-parameter, read-only lookup with no output schema, the description adequately previews the return contents (sale status, per-action pricing, ownership rules, notices) and the pricing basis. Annotations cover the safety profile. The only real gap is usage routing against the sibling tools.

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?

There is a single parameter with 100% schema description coverage, so the schema already explains 'the extension without a dot, e.g. no, com or eu'. The description does not add format or validation detail for the parameter beyond what the schema states, so the 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?

The description names the specific resource (one TLD/extension) and enumerates the data returned: availability for sale, price per action, ownership restrictions, and registry notices. That is far more than a restatement of the name 'requirements'. It does not, however, explicitly contrast itself with list_extensions or check_domain, so an agent must infer the boundary.

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?

There is no statement of when to use this tool versus the siblings. An agent can infer 'per-TLD detail lookup' from the content, but the description never says to call list_extensions for the catalog or check_domain for availability, nor does it state any prerequisite (e.g. that the TLD must be known first).

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