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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the description's real added value is the data-freshness caveat ('at the latest data update', 'Not re-checked at query time') and the auth-tier gating of results and filters. It stops short of describing pagination depth or rate limits beyond the passing plan reference in the schema.

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-loads the resource and scope, then caveats and verification workflow in descending priority; every sentence carries information. The opening sentence is dense, packing six TLDs, two length classes and three pattern notations into one clause, which costs a little readability.

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?

Given an output schema exists, return values need no explanation, and the definition still covers the items an agent must know to call it correctly: data staleness, account-tier limitations on results and filters, and which sibling to use before acting on a result.

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%, so the baseline is 3, but the description adds real meaning the schema lacks: it defines the CVCV/VCVC/CCVV pattern notation (C = consonant, V = vowel) that the `type` enum only labels as 'Pattern type filter', and notes that filters are unavailable without an account.

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 precise verb and resource (search short unregistered domain names) plus the exact scope: six TLDs, 3-letter and 4-letter names, and CVCV/VCVC/CCVV shapes. It also names the sibling tools it is not (available, bulk_available), so an agent can route without opening another schema.

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?

Explicitly gives when-to-use and when-not-to-use: this is a snapshot list, not a live check, so 'confirm with available or bulk_available before registering.' It also states the account-level precondition that changes behavior (without an account only .ai is shown and filters are unavailable).

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