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

With no annotations, the description carries the full burden and does well: it discloses the refusal behavior for documents whose home is an existing design, the `compose-preview-decision/v1` choice returned to the person, and the form-elicitation fallback path. It does not mention permissions/auth requirements beyond what the `token` param schema covers.

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 action is front-loaded and each sentence adds information (mode choice, copy rationale, refusal/elicitation behavior). It is somewhat dense with backtick-heavy phrasing, but nothing is wasted.

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?

An output schema exists so return values need no explanation, and the description covers the creation semantics, the catalogPin constraint, and the refusal/elicitation behavior for a mutation tool with no annotations. Adequate for correct invocation, though auth/permission context is left implicit.

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 high (83%), so the baseline is 3, but the description adds genuine semantic value: it explains the relationship and trade-off between `document` and `fromDesignId` (the catalogPin constraint) that the schema merely names, guiding correct parameter choice.

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 (Create) and resource (a design), and immediately distinguishes its two modes of creation via `document` vs `fromDesignId`. This separates it from siblings like ui_builder_replace_design_document and ui_builder_get_design without the agent needing to open any schema.

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 explicit guidance that 'Copying is usually right' and explains why a supplied document can be refused when its `home` is an existing design on the server. It provides clear conditions for choosing a path, though it does not name sibling alternatives (e.g., replace_design_document) for the update case.

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