read_wechat_image

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

Annotations already indicate readOnlyHint and destructiveHint, so the safety profile is covered. The description adds genuine behavioral disclosures beyond that: it explicitly states encrypted DAT files are not decrypted ('加密DAT不解密') and that the path does not prove session ownership ('路径不证明会话归属'). These are warnings about the tool's limitations that an agent would not otherwise know, justifying a 4.

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?

One dense sentence with three distinct clauses, each earning its place: the action/return, the path constraint, and the behavioral caveats. Information is front-loaded with the core function first, followed by the necessary restrictions. No filler or repetition.

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 read-only tool with one parameter and no output schema, the description covers the key operational constraints (whitelist path, no decryption, session attribution caveat). It could mention error behavior for invalid paths, but that is a minor gap given the simple scope and the standard MCP image return type.

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 0%, so the description must carry the meaning of source_path. It does so by defining it as a local WeChat standard image path inside the whitelist ('只能使用本地附件白名单路径'). It doesn't detail path format or error handling, but given a single simple parameter, this is adequate and clearly compensates for the empty schema.

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 (读取/read) and resource (本机微信标准图片, local WeChat standard image) and clarifies it returns a native MCP image. The constraints on path whitelist and encryption disambiguate it from sibling read tools like read_article_image or read_merged_forward, making its scope clear without opening schemas.

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 gives a concrete usage rule: '只能使用本地附件白名单路径' (only use local attachment whitelist paths), which tells the agent what inputs are acceptable. It implies this is for standard WeChat images rather than article images or merged forwards, but it stops short of explicitly naming alternatives or when-not-to-use scenarios, so it earns a 4 rather than a 5.

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