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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so safety is covered and the description only needs to add generation-specific context. It adds that the record is assembled from parts, but says nothing about the output form (a raw 'v=DMARC1; p=...' string?), whether inputs are validated or normalized, or whether addresses must carry a mailto: prefix.

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?

A single front-loaded sentence with no filler, and the required parameter (policy) leads the enumeration. The terseness is close to the point of under-specification, but no sentence is wasted.

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?

With six parameters, zero schema descriptions, and no output schema, an agent needs the description to explain parameter meaning and return shape. One sentence cannot cover that: failureReporting is entirely absent and the produced record's format is never stated, leaving gaps an agent would have to guess at.

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 0%, so the description carries the full burden, and it does not fully discharge it. It names policy, subdomainPolicy, report addresses, and percentage, but never mentions failureReporting (the sixth parameter), never distinguishes rua (aggregate) from ruf (forensic) address lists, and gives no format guidance for the URI arrays.

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+resource ('Assemble a DMARC record') and enumerates the inputs it consumes, which clearly marks it as a generator rather than a validator like check_dmarc. It stops short of explicitly naming the sibling it differs from, but the build-vs-check distinction is readable from the text.

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: an agent can infer that this is the tool to reach for when it needs to produce a DMARC record rather than inspect one. There is no explicit 'use this instead of check_dmarc when...' statement, no prerequisites, and no guidance on whether the result should then be validated or published.

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