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

With no annotations, the description carries the full burden. It does add useful behavior: the 20-name cap, the RDAP+DNS data sources, and the returned attributes — enough to signal a non-destructive lookup. But it says nothing about rate limits, what happens with malformed domains, or partial failures in a batch, which matter for a bulk query tool.

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?

Two tight sentences, front-loaded with the core capability and the batch-size limit, then the use case. Every clause carries information; nothing is redundant with the title.

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?

An output schema exists, so return-value explanation is not required, yet the description still names the key fields. Modes, cap, and data sources are all covered. The only real gap for a 2-parameter tool is the string input format, which leaves an agent guessing at call syntax.

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 0%, so the description must compensate. It does well on the relationship between the two parameters — either up to 20 names at once, or one name expanded across a list of TLDs with examples (com, ai, io) — but both fields are typed as plain strings and neither the schema nor the description states the delimiter or format (comma-separated? newline-separated?) an agent must use.

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 ... domain names ... for registration') plus the mechanism (RDAP and DNS) and the returned fields (available or taken, registrar, expiry). It is clear what the tool does, though it does not explicitly distinguish itself from the closely related domain_whois sibling, which also queries RDAP-style registration data.

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 closing sentence gives an explicit use case ('brainstorming product names and finding free domains'), so an agent knows when to reach for it. It stops short of naming alternatives or exclusions — notably domain_whois and dns_lookup sit right next to it and overlap for single-domain lookups.

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