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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is known. The description adds meaningful behavior beyond this: 'Live lookups - not cached' and 'Automatically parses SPF and DMARC policies from TXT records' – both of which are useful and not inferred from the annotations. No contradiction with 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?

The description is front-loaded with the core purpose, then provides behavioral details, use cases, and an alternative. Every sentence carries unique value; there is no filler or redundancy.

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?

The description covers purpose, behavior, and usage comprehensively, with no output schema to worry about. However, it does not mention error behavior (e.g., invalid domain, NXDOMAIN) or the response format, which would be useful for a live lookup tool. Overall it is still well-rounded.

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% for both domain and types parameters. The description's list of record types and default behavior duplicates what the schema already provides. It does not add new parameter-level semantics, so the baseline of 3 is appropriate.

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 and resource: 'Full DNS record lookup for a domain' and enumerates the exact record types returned (A, AAAA, MX, NS, TXT, CNAME, SOA, CAA). This clearly distinguishes it from sibling tools like name_check, email_check, and url_check, and it even offers a fallback via request_tool for unsupported lookups.

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?

Explicit use cases are provided: 'Use this for infrastructure audits, email deliverability setup, domain verification, and security checks.' It also gives an explicit alternative: 'Need a record type or lookup this does not support? Describe it via the request_tool tool.' This addresses both when to use and when not to use the tool.

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