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

Beyond the annotations (readOnlyHint, idempotentHint, destructiveHint), the description discloses critical behavior: it returns a watermarked preview URL, an editor URL, and an App Store link; the server refuses disallowed scenes; nothing is saved to an account; and links expire after 30 days. No contradiction exists between the description and the annotations.

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 front-loaded with purpose, then returns, then constraints and persistence details. Each sentence adds a distinct piece of information with no repetition or padding, making the size appropriate for the tool's complexity.

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?

Given the output schema exists, the description needn't fully enumerate return values, yet it still names the three URLs. It covers limits, content restrictions, server refusal, and ephemeral behavior, leaving no critical gap for an agent to call the tool correctly. The only slight omission—routing to list_templates—is already in the schema.

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?

With 100% schema coverage, the baseline is 3. The description adds meaningful restrictions not fully in the schema: total character limits (up to 30 messages and 4000 characters) and forbidden message content (login codes, passwords, payment details), which go beyond the schema's 'links are not accepted' note. This helps avoid rejected requests.

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 ('builds'), a concrete resource ('a chat mockup in a Mimicly template'), and the intended use cases (story, video, lesson, design, presentation, demo). This clearly differentiates it from the sibling tool list_templates, which only lists templates, by focusing on creation.

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 gives positive usage contexts and explicit negative exclusions ('not for posing as a real person... not for misleading someone'). It does not explicitly mention the sibling tool list_templates as a prerequisite, though the input schema does reference it, so the guidance is clear but slightly indirect.

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