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

Annotations already declare readOnlyHint and openWorldHint, and the description adds meaningful operational context beyond them: it is DNS-based, it does not expand nested SPF includes, and it returns prioritised findings with fix hints and a 0-100 score. It does not discuss rate limits, cache/TTL behavior, or failure modes, so it falls short of a 5.

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?

A single dense sentence front-loads the purpose and then packs the parsed record types, return shape, and the include-expansion limitation without filler. It is long, but every clause carries distinct information an agent needs.

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 stating the return shape (prioritised findings, fix hints, 0-100 score) and the key limitation (nested includes not expanded). For a read-only, one-parameter audit tool, nothing an agent needs in order to call it correctly is missing.

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% and there is only one parameter, so the baseline is 3. The description adds nothing about the domain argument (e.g. apex vs subdomain, IDN handling) beyond what the schema already states.

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 uses a specific verb+resource pair ("Email deliverability and spoofing-protection audit for a domain") and then enumerates exactly what is parsed (SPF mechanisms, DMARC policy, DKIM selectors, MX, BIMI, MTA-STS, TLS-RPT), which clearly separates it from siblings like domain_dns or email_check.

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?

Scope is implied through the content list and the note that nested SPF includes are not expanded, but there is no explicit when-to-use statement and no routing to alternatives (e.g. domain_dns for raw records or email_check for mailbox validation). The agent must infer the boundary from the sibling names.

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