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

The description discloses substantial behavior beyond the readOnlyHint/openWorldHint annotations: it names the backend (Cloudflare DNS-over-HTTPS), the 5-second timeout, and the complete JSON status contract with ok, not_applicable, timeout, and error variants. It also tells the agent how to interpret not_applicable versus error, which is exactly the kind of behavioral nuance annotations cannot express.

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?

Every sentence earns its place: purpose, use case, infrastructure, timeout, and return-status semantics are packed into four tight sentences with no filler. The most important information is front-loaded and the status contract is clearly structured.

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 that there is no output schema, the description fully compensates by specifying the exact status shapes and interpretation guidance. It covers success, absence, timeout, and error, and lists the parsed tags, making the tool self-sufficient for an agent to invoke and understand the 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 description coverage is 100% and the parameter is simple. The description adds value by clarifying that the supplied domain is the base domain to which '_dmarc.' is prepended, and reinforces the accepted format via example.com. This goes slightly beyond the schema's rejection list, so a 4 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?

Description states a specific verb and resource: 'Find and parse the DMARC policy at _dmarc.<domain> into its tags'. It also names the exact policy tags and the security question it answers (rejected, quarantined, reported), which distinguishes it from sibling DNS tools like dns_lookup, dossier_spf, and dossier_dkim.

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 description gives clear usage context: 'Use to see whether spoofed mail is rejected, quarantined or only reported'. However, it does not explicitly contrast it with alternative tools such as dossier_spf or dossier_dkim, nor state when NOT to use it, so it falls short of a full 5.

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