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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety bar is low. The description still adds real value: it discloses that this is a free public API requiring no auth, that it performs an external DNS lookup at _dmarc.<domain>, and that it evaluates tags and flags risky configurations rather than just returning raw records.

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 sentences, zero filler, and the core action is front-loaded after a short access note. Every clause earns its place by adding scope (DNS location) or behavior (parsing and flagging).

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 values need not be described, and annotations cover the safety profile. The description covers what is queried and what is evaluated; the only minor gap is the lack of guidance on error cases such as a domain with no DMARC record.

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% and there is a single parameter, so the schema already carries the load. The description adds one useful nuance — that the domain is looked up at the _dmarc.<domain> prefix, implying the caller passes the bare domain — but no format or edge-case guidance.

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 ('Look up the DMARC record'), names the exact DNS location ('_dmarc.<domain>'), and enumerates the work done (parse policy/alignment/reporting tags, flag missing or permissive settings). This clearly separates it from sibling email-auth tools like tools_spf_record_checker and tools_dkim_record_checker.

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?

Usage is only implied by the domain-name checker naming convention and the note that it is a 'Free public API'; there is no explicit when-to-use statement, no mention of choosing it over the SPF/DKIM checkers, and no prerequisites or exclusions. Adequate but clearly gapped.

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