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

With annotations already declaring readOnlyHint=true and destructiveHint=false, the description adds valuable behavioral detail: the a= tag limitation (VMC vs CMC not determined), the DMARC enforcement prerequisite, and the specific validation of l= and a= tags. The return behavior ('Returns findings for a missing/malformed record or unmet prerequisites') is also disclosed.

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: core action is front-loaded, followed by technical detail, limitation, prerequisite, return behavior, and usage context. The structure flows logically, and despite the density of information, there is no redundancy or fluff.

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?

For a moderate-complexity tool with an output schema (which removes the need to describe return structure) and comprehensive parameter definitions, the description covers validation logic, limitations, prerequisites, and use cases thoroughly. Minor gaps include no mention of network/DNS failure edge cases or interaction with the format/force_refresh parameters, but these are adequately handled by the output schema and parameter descriptions.

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% with each parameter clearly documented (e.g., 'Auto-detected if omitted' for format, 'Bypass cache' for force_refresh). The description maintains the baseline 3 by not detracting from the schema but adds minimal parameter-specific value beyond it, sticking to domain-level validation context instead.

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 opens with a specific verb+resource construction ('Check the BIMI brand-logo record at default._bimi.<domain>') and details exact validation logic (l= tag, a= tag, DMARC prerequisite). The scope is precisely delimited, and the focus on BIMI-specific checks (as opposed to the many sibling DNS-check tools) makes the purpose unambiguous.

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 provides clear use context ('Use to assess brand-indicator readiness in inboxes' and 'Part of the scan_domain audit'). However, it does not name alternative tools or explicitly articulate when NOT to use it, which would earn a 5.

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