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

Annotations already declare read-only and non-destructive behavior. The description adds important behavioral context beyond annotations: it explicitly warns that the URL is generated without checking DNS existence or certificate validity, and that it may not resolve with external DNS lacking a webmail entry.

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?

Two tightly written sentences with zero waste. The purpose is front-loaded and the important caveat follows immediately, making it easy to scan.

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, but the description makes clear that the tool returns a constructed webmail URL and explains its limitations. For a one-parameter, read-only utility, nothing essential is missing.

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 the single 'domain' parameter is already documented. The description adds the URL construction pattern, which clarifies how the parameter is used, but does not add constraints or format details beyond what the schema provides.

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: constructs the webmail access address for a domain, including the exact URL scheme. It is clearly distinguishable from sibling read/status tools because it only generates a URL rather than measuring or verifying anything.

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 for when the tool is appropriate and explicitly states a key when-not condition: it is not a measurement and does not verify DNS or certificates. It does not, however, name an alternative tool to use when verification is actually needed.

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