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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description goes well beyond that by disclosing three diagnostic conditions the raw records cannot show: duplicate SPF causing permerror, DMARC/DKIM at the apex being unread, and TXT strings over 255 bytes. That is exactly the kind of behavioral context annotations cannot carry.

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?

Purpose is front-loaded in the first clause, and the failure-mode list and the usage warning follow in a logical order. It is a long description, but nearly every clause carries distinct information; the embedded parenthetical enumerations of record types and underscore names make sentences dense rather than 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 no output schema, the description does the work of telling the agent what comes back: each record identified by type or service ownership token, plus four underscore names, plus three flagged mistakes. What it does not state is the response shape or how the identification and warnings are labeled in the output, which is the remaining gap for a no-output-schema tool.

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?

Only one parameter and schema coverage is 100%, and the schema description already explains the underscore-prefixed name behavior, so the schema does the work. The description reinforces the underscore names in prose but adds no new syntax or format detail beyond the schema. Baseline 3 applies.

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 ('Every TXT record on a domain') and immediately scopes it as an aggregate: all record types identified plus the four underscore names a receiver reads. That clearly distinguishes it from the narrow siblings check_spf, check_dkim, check_dmarc, check_mta_sts and check_bimi without needing to open any schema.

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?

Gives an explicit usage rule with a reason: 'Use this before concluding a record is missing, because the usual cause of a missing DMARC record is a DMARC record at the wrong name.' It does not name the individual checker as the alternative to use for a single-record confirmation, so the routing guidance is strong but not exhaustive.

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