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

Annotations already declare readOnlyHint, openWorldHint, and destructiveHint=false, so the safety profile is covered. The description adds the selector default behavior but doesn't say the lookup is a live DNS query, how a missing record is reported, or whether results are cached — real behavioral context for an open-world read.

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 short sentences, front-loaded with the action and resource, and the second sentence carries only the non-obvious default. No waste.

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?

A simple two-parameter read tool with annotations covering safety and no output schema to paraphrase. The description covers the essentials; only the absent-record behavior and query nature are missing, which is minor at this complexity.

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 0%, so the description must carry parameter meaning. It does add genuinely useful information the schema lacks — the selector defaults to 'default' — but 'domain' and 'selector' are otherwise unexplained (e.g. that a selector follows the DKIM-style selector convention, or the allowed character set). Partially compensates for the coverage gap.

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 ('Read the BIMI record') scoped to a domain and selector, which clearly separates it from siblings like check_dkim, check_dmarc, and check_mta_sts. It doesn't explicitly name a sibling, but the resource is unique enough that disambiguation isn't a concern.

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 implied — an agent checking BIMI configuration would call this — but there is no explicit when-to-use, no prerequisites, and no mention of alternatives or follow-up tools. Adequate but leaves the agent to infer context.

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