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

Annotations already declare read-only, idempotent, open-world, and non-destructive behavior. The description adds valuable context beyond that: it never fetches or cryptographically matches the live certificate, it resolves MX hosts when no port is given, and 'No auth or destructive actions' reinforces the safety profile.

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 compact but information-dense, starting with the core purpose and then layering behavior, limitations, alternatives, and use cases. Every sentence contributes either to selection, invocation, or expectation-setting; there is no filler or repetition of schema data.

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 present, the description compensates by listing returned data categories: parsed usage, selector, matching type, certificate data, syntax errors, and advisories. It also covers behavioral nuance, limitations, related tools, and intended workflow context, making it complete for an agent to select and invoke correctly among many DNS/email siblings.

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 descriptions already cover 100% of the parameters, including domain format, port defaults, and protocol enum. The description adds semantic value by explaining how port and protocol combine into the constructed TLSA query (`_<port>._<protocol>.<domain>`) and how absence of port changes resolution behavior from explicit query to MX host discovery.

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 opens with a specific verb and resource: 'Read-only TLSA/DANE DNS record check.' It clearly explains two operational modes (no port -> MX-host TLSA records; explicit port -> `_<port>._<protocol>.<domain>`) and explicitly differentiates itself from sibling check_smtp_tls by noting it does not fetch the live certificate.

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 gives explicit guidance: 'Use before publishing DANE records or troubleshooting DANE handover,' and says to pair it with check_smtp_tls when SMTP certificate evidence is needed. It also states what the tool does NOT do, which clarifies when not to rely on it.

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