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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so safety is covered. The description adds value beyond that by disclosing the return shape (styled prompt stack plus an aspect_ratio to forward), which is important given there is no output schema.

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 compact sentences, front-loaded with the core concept and the style choices. The aspect_ratio forwarding instruction is stated twice (once in the body, once implied again), a minor redundancy.

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 read-only, no-output-schema tool, the description covers what it does, the options, and what comes back. The only meaningful gap is sibling disambiguation versus apply_iphone_realism and other apply_* style tools.

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 each enum value is documented in the schema, so the schema does the heavy lifting. The description reinforces the aspect_ratio round-trip but adds no new syntax or constraint beyond what the schema already provides, making baseline 3 correct.

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 ('apply', UGC style) and enumerates the four concrete style variants, so an agent knows exactly what the tool produces. It does not, however, distinguish itself from near-duplicate siblings like apply_iphone_realism or apply_style, even though phone_shot is described as 'iPhone-style snap'.

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 a clear downstream workflow ('pair it with generate_image and pass that aspect_ratio along'), which is genuinely useful. But there is no explicit when-to-use/when-not guidance and no routing away from apply_iphone_realism, which overlaps heavily with the phone_shot variant.

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