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

Annotations already declare readOnly, idempotent and non-destructive, so 'without changing anything' largely repeats them. The one genuinely additive fact is that output is a render using sample data rather than real recipient data, but return format and what the preview contains are left unstated.

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?

One tight sentence with zero waste, and the resource scope is front-loaded before the sample-data qualifier.

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 single-parameter read-only preview with no output schema, the definition conveys enough to call it correctly. Minor gap: it doesn't say what the preview response looks like or whether sample data is selectable.

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 single template_id parameter already documents both the UUID and gallery-id forms with the sibling to source it from. The description adds nothing beyond the schema, so baseline 3 is 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?

Specific verb (show/preview) with the resource (postcard template) and its three sources (yours, Spur default, gallery design), plus the key qualifier that it renders with sample data. It distinguishes preview from the get/update/delete template siblings implicitly, though it never names get_postcard_template or preview_postcard_campaign directly.

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 phrase 'without changing anything' implies a safe inspection use case, and 'rendered with sample data' hints at when you'd want this over a plain fetch. But there is no explicit when-to-use/when-not statement or named alternative among the many preview/get siblings.

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