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

Annotations already declare readOnlyHint=false, idempotentHint=false and openWorldHint=true, so the safety profile is covered. The description adds real value beyond them: the live animated preview shown in the conversation, the exact return values, and the partial-update semantics ('everything else is kept'). It does not mention latency or failure modes of an open-world generation call.

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?

Three sentences, front-loaded with the primary action and return values, then the prerequisite, then the update mode. Dense but every sentence carries actionable information; the middle return-values sentence could arguably be tighter.

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, the description explicitly enumerates the return payload (preview id, preview link, download link), covers the zero-required-parameter create vs. update branching, and points to the sibling needed to fill nested object keys. Nothing an agent needs to invoke it correctly is missing.

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 100%, so the schema already documents all eight parameters including the conditional requirements on language and design_id. The description reinforces the update contract with base_preview_id but adds no syntax or format detail the schema lacks, so the baseline of 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?

The description names a specific verb (generates) and resource (the user's site) plus the model (8B) and the inputs it consumes (design, texts, colors, fonts, photo queries). It also distinguishes itself from the siblings by requiring get_design_brief and explore_designs outputs as inputs.

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 states explicit prerequisites ('Call get_design_brief first to see the fields') and gives a clear when-to-use branch for the modify case, naming base_preview_id as the alternative path and specifying that only changed values need to be sent.

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