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

The annotations already establish that this is a read-only, idempotent, non-destructive, non-open-world operation. The description adds useful behavioral detail by explaining that it previews truncation across three specific clients and emits warnings such as no sender name, all caps, or empty preview.

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 two sentences, front-loads what the tool does, and follows with a direct usage recommendation. There is no unnecessary repetition or filler.

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?

For a simple read-only preview tool with complete schema coverage and rich safety annotations, the description supplies the missing conceptual context: the clients previewed, the kind of truncation shown, and the warning categories. An agent has enough information to select and invoke it correctly.

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 all three parameters are already documented in the input schema. The description reinforces the roles of sender name, subject line, and preview text but does not add syntax or optionality details beyond what the schema provides, making the baseline 3 appropriate.

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 states a specific verb and resource: it shows how a cold email's sender name, subject line, and preview text are truncated in Gmail desktop, Gmail mobile, and Outlook. It also names the warning conditions it reports. This is clearly distinguishable from all sibling analysis and deliverability tools.

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 gives a clear usage context: use it to check whether a subject line fits before sending. It does not list when not to use it or name alternative sibling tools, but the intended timing is explicit.

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