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

Annotations already declare readOnly, idempotent, and non-destructive, so the safety bar is low; the description adds the substantive behavior that output is a rendering populated with sample data rather than the stored template itself. It does not describe what the sample data is or whether rendering costs anything, which keeps it short of a 5.

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 sentence that front-loads the scope of valid inputs and ends with the key non-mutation guarantee. No 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?

With no output schema present, the description does well to state that a rendering is produced with sample data. It stops short of clarifying the return form (image, HTML, link) or how sample data is chosen, a minor gap for a preview tool.

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% and the parameter already documents that the id comes from spur_list_letter_templates and may be a UUID or gallery id. The description's parenthetical about template sources restates that rather than extending it, so baseline 3 applies.

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?

Specific verb 'Show' plus resource 'letter template', with scope enumerated (yours, Spur default, gallery design) and outcome stated (rendered with sample data). An agent can distinguish it from spur_preview_message_template and spur_preview_postcard_template purely from the resource named.

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?

'Without changing anything' clearly signals a safe preview/inspection context, implying use before committing to sending. It does not, however, name an alternative such as spur_get_letter_template for fetching raw template data, so the when-to-use-vs-sibling boundary is only inferred.

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