Download and validate PNG, JPEG, or WebP images from a public URL, save them to disk, and return the absolute file path.
按图片 URL 下载并校验 PNG/JPEG/WebP，自动落盘返回绝对路径；不会附带供应商 API Key。
| Name | Required | Description | Default |
|---|---|---|---|
| url | Yes | 公开 HTTP(S) 图片 URL | |
| output_dir | No | 可选绝对输出目录；默认配置目录。异步任务查询默认沿用提交目录。 |
| Name | Required | Description | Default |
|---|---|---|---|
| path | Yes | ||
| bytes | Yes | ||
| reused | Yes | ||
| sha256 | Yes | ||
| mime_type | Yes |
Changes observed during successful MCP inspections.
v0.3.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations cover the safety profile (openWorldHint, idempotentHint, non-destructive), but the description adds real context beyond them: it validates specific formats, persists to disk, returns an absolute path, and explicitly notes it will not carry the vendor API Key. That security disclosure is genuinely useful. It stops short of describing failure modes or overwrite behavior.
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?
A single front-loaded sentence with no filler; the core action comes first and the security caveat is a tight trailing clause.
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?
An output schema exists so return values need no explanation, and annotations cover safety. Combined with format-validation and no-API-key disclosures, the description is nearly complete; only edge behaviors (overwrite, network failure) are absent.
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%, so url and output_dir are already fully documented, including the default-directory and async-task-inheritance behavior. The description adds little parameter meaning beyond restating that output goes to disk, so baseline 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?
States a specific verb (下载/download) and resource (图片/image) plus the scope of what happens (validate PNG/JPEG/WebP, write to disk, return absolute path). This clearly distinguishes it from the sibling generation/edit tools, which produce images rather than fetch them.
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 the use case (fetch an image from a URL) but never states when to use this versus generate_image or edit_image, nor any prerequisites or exclusions. Usage is inferable but not guided.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.