Fetch a permanent material from WeChat Official Account using its media ID and write the binary response to the specified save_path, without overwriting existing files.
获取永久素材；二进制响应写入本机 save_path 且不覆盖。
| Name | Required | Description | Default |
|---|---|---|---|
| media_id | Yes | ||
| save_path | Yes |
| Name | Required | Description | Default |
|---|---|---|---|
No arguments | |||
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already mark the operation as read-only, idempotent, and non-destructive. The description adds valuable behavior beyond those annotations: the binary response is written to the local save_path and existing files are not overwritten. This is useful behavioral context for an agent deciding how to invoke the tool.
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 entire description is one compact sentence that states the resource, the response format, the side effect, and a critical constraint. Every clause provides useful information and nothing is wasted.
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 annotations covering safety, an output schema present, and only two self-explanatory parameters, the description provides enough to call the tool correctly. The main missing detail is what happens when save_path already exists, since 'does not overwrite' implies some behavior but does not specify the outcome.
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 compensate. It does add meaning for save_path by specifying local binary write and no-overwrite behavior, but media_id is not elaborated beyond its self-explanatory name. Overall, partial compensation keeps this at an acceptable level.
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 action 'get permanent material' and conveys that the result is binary data written to a local path. It distinguishes permanent materials from temporary ones, but does not explicitly differentiate it from list_materials or other retrieval siblings.
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 this tool is for retrieving permanent material binaries and saving them locally, which gives some usage context. However, it never explicitly states when to use this tool over alternatives such as list_materials or download_temp_media, nor does it state exclusions.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.