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

Annotations declare readOnlyHint=false, idempotentHint=true, destructiveHint=false, but the description is silent on these traits. This matters because 'preview' implies a side-effect-free read, while the annotations say it is not read-only (and an idempotency_key parameter is required to make it so) — the description never explains that the call may materialize/persist something.

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?

A single front-loaded sentence with no filler, but it is thin rather than efficient — the brevity comes from omitted information, not from tight phrasing. There is no wasted text, so it is not a 2, but it under-serves the reader.

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 3-parameter tool with no output schema and no schema descriptions, the definition should explain inputs, return shape, and the surprising non-read-only semantics. It does none of these, leaving the agent unable to invoke the tool correctly beyond guessing.

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 0%, so the description carries the full burden, and it explains none of the three parameters. 'email_type' (with a lowercase/snake_case pattern), 'request_id', and especially 'idempotency_key' derive no meaning from the text; 'sample variables' hints at inputs that aren't even in the schema.

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 recognizable action (preview an email) but is vague about the resource: 'sample variables' is undefined, and it never says it renders an email template. It also fails to distinguish itself from close siblings such as yardstick_email_templates_preview_customization and yardstick_email_drafts_preview.

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?

No when-to-use guidance, no prerequisites, and no routing to alternatives. An agent cannot tell from the text whether this previews a saved template, a draft, or a customization, nor when to prefer one of the three preview siblings.

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