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

Annotations already cover read-only, idempotent, non-destructive, and closed-world behavior, yet the description adds real value beyond them: cost ('Free'), an auth exception for custom:cp_... bases, and the return contract (valid plus normalized style, or errors with path/message) despite there being no output schema. It does not cover failure modes such as invalid input or unknown base presets.

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?

Two dense sentences with no filler: the free/auth caveat, the validation input modes, and the return shape. Front-loaded with the practical facts an agent needs before calling.

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 supplies the return shape and error structure, which is exactly what's needed. Remaining gaps are minor: behavior with zero arguments, whether style and basePreset may be combined, and what 'normalized style' entails.

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 0%, so the description must carry the load, and it does explain the role of all three parameters and their relationship: a full style document OR a basePreset plus overrides. It stops short of stating precedence between style and overrides, or the exact basePreset string format beyond the custom:cp_ hint.

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?

States a specific verb and resource: check a caption style document (or basePreset + overrides) against the renderer schema. The phrase 'without saving' implicitly separates it from sibling mutations such as save_custom_preset and update_custom_preset, though no sibling is named explicitly.

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 'without saving' framing implies a pre-save validation use case, and the auth caveat tells the agent when a key is needed for custom:cp_... bases. However, it never explicitly says 'call this before save_custom_preset' or what to do if validation fails, so the routing guidance is only implied.

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