Download media thumbnail to local disk

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

With no annotations, the description carries the full burden. It discloses key behaviors: uses a proxy to avoid exposing direct source links, and writes to disk (side effect). However, it does not mention idempotency, overwrite behavior, or potential side effects beyond saving.

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 a single, concise sentence that front-loads the main action and includes only essential details. It is efficient and well-structured.

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?

The description explains the action and side effect but does not mention the return value or error behavior. Since there is no output schema, this information may be needed for full usability, but the scope of the tool is simple enough that the description is adequate for basic 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 100% (both parameters have descriptions). The tool description adds no extra parameter semantics beyond what's already in the schema, so a baseline score of 3 is appropriate.

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 clearly states the tool's purpose: saving the thumbnail returned by extract_media to disk. It specifies the exact action ('落盘'), the source ('extract_media 返回的封面图'), and adds context about using a proxy, which distinguishes it from sibling tools like download_media.

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 description implies usage after extract_media, but does not explicitly state when to choose this over the sibling tools. It lacks direct guidance on alternatives or conditions for use, making it only implicitly clear.

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