check_dmarc

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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, so safety traits are covered. The description additionally discloses 'single GET, no auth, no side effects', which reinforces and adds specificity. It also mentions it returns warnings and a policy strength assessment, which is useful behavioral context. No contradiction found.

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 concise, front-loaded with purpose, then usage, and then technical details. Every sentence earns its place without fluff. It is about 70 words for a complex tool, which is efficient.

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?

Given the tool's moderate complexity (fetching DNS record and parsing) and that no output schema exists, the description essentially provides the output structure (returns parsed tag map, policy strength, warnings). It also covers caveats (multiple records) and authentication requirements (no auth). A slight gap: it doesn't mention what happens if the record is missing, but overall it is thorough.

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 100%, so the parameter 'domain' is well documented in the schema. The description adds context by emphasizing it is 'domain name only, no URL, path, or port', which prevents misuse. However, it does not deeply expand beyond the schema, so a 4 rather than 5.

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 has a clear verb ('fetch and parse') and resource ('_dmarc TXT record'), with specific scope. It explicitly states what it returns and lists fields (tag map, policy strength, etc.), distinguishing it from sibling tools like check_spf and check_sender_requirements.

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?

It explicitly explains when to use this tool ('for DMARC policy review') and when to use an alternative ('use check_sender_requirements for combined Google/Yahoo SPF+DKIM+DMARC pass/fail verdict'), which is excellent guidance compared to most tool descriptions.

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