download_cover

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

With no annotations, the description carries the behavioral disclosure burden. It clearly states that the file is saved to a 'covers' subdirectory by default, that an alternate output directory can be supplied, and that the return value is a success message with the saved path. It omits details like overwrite behavior or directory creation, but the main side effects are disclosed.

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 compact, front-loaded with the core purpose, and then organized into clear sections for parameters and return value. Every sentence contributes necessary information, and there is no unnecessary repetition of schema fields.

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 simple two-parameter download tool, the description covers the action, default directory, optional override, and return message, and an output schema exists. It is not fully complete because it lacks guidance on error scenarios, overwrite behavior, or how this tool relates to sibling downloading tools, but it is sufficiently complete for basic selection and invocation.

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 fully explain parameters. It does: album_id is defined as the album ID with an example, and output_dir is defined as an optional output directory with the default behavior explicitly stated. This adds meaning well beyond the bare schema property names.

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 and resource: '下载特定本子的封面图片' (download the cover image of a specific album). This is clear and distinct from the main resource, but it does not explicitly differentiate itself from download_album or download_photo, whose scope could overlap with downloading cover images.

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 intended use is implied by the purpose statement: use this tool when you need an album's cover image. However, the description gives no explicit guidance about when to prefer this over sibling tools like download_album or download_photo, nor does it mention any exclusions or alternatives.

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