pdf_render

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

With no annotations provided, the description carries the full behavioral burden and largely succeeds: it discloses the default return mode (base64 image viewable by the agent), the save-alternative (writes file and returns only path info), the region subsetting behavior with the magnifier effect, and the full coordinate convention (top-left origin, y-down, pt units). Minor gaps remain around error behavior (wrong password, invalid page number) and file-overwrite semantics, but the core behavior is clearly 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?

Three tightly packed lines: the lead sentence states purpose and use cases, then two bullet-style lines cover return modes and region/coordinate semantics. Every sentence earns its place, key behavior is front-loaded, and there is zero filler or restatement of the schema.

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 9-parameter tool with no annotations and no output schema, the description covers the essentials an agent needs: return formats in both modes, region semantics, and coordinate units, while the schema handles dpi/scale precedence and default values. What's missing is error-behavior context (e.g., behavior on wrong password or out-of-range page) that would fully complete the picture for a tool with two required parameters.

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%, so the baseline is 3. The description nevertheless adds genuine value beyond the schema: it explains the region+scale synergy as a '放大镜' (magnifying glass), generalizes the coordinate system beyond the region parameter, and defines pt units (1pt=1/72 inch) — none of which the schema states. This justifies one point above baseline.

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 opens with a specific verb+resource+output: '把 PDF 某一页栅格化成图片（PNG/JPEG）' (rasterize a specific PDF page into an image). It further lists concrete use cases — viewing layout, zooming into details, verifying restoration results — which collectively distinguish it from the siblings pdf_info (metadata) and pdf_extract (content extraction) without ambiguity.

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?

Gives explicit use-context through '可用于：整体查看版面、放大局部核对细节、验证还原结果', telling the agent when rendering is the right operation. However, it never names the sibling alternatives (pdf_info/pdf_extract) nor states when NOT to use this tool, so it stops short of the explicit when/when-not/exclusion standard.

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