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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the safety profile is clear. The description adds meaningful behavioral context: it returns both 'ours' and 'theirs' verdicts, whether they agree, and parsed envelope/headers, which goes beyond the annotations without contradicting them.

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?

The description is a single, dense sentence that front-loads the primary purpose and key return fields, with no superfluous content. It earns its place efficiently.

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?

There is no output schema, so the description compensates by explaining the return values (ours, theirs, agree, parsed envelope/headers). Given the moderate complexity of 4 parameters and the clear input requirements, the description is complete enough for an agent to select and invoke the tool correctly.

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%, so parameters are fully documented in the schema. The description adds a general reference to 'envelope/headers' but does not provide additional parameter-level meaning beyond what the schema already gives, so baseline 3 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?

The description clearly states the tool re-verifies SPF, DKIM, DMARC, and ARC from raw email, which is a specific verb and resource. It also distinguishes itself from siblings like get_dmarc_summary or scan_domain by focusing on raw header analysis and returning independent vs. sender auth results.

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 context on when to use it (spotting forged or mismatched auth results) and notes that no account is needed, implying a low-friction usage context. It does not explicitly list exclusions or alternatives, but the use case is well implied.

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