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

Annotations already declare readOnly/idempotent/openWorld, so the bar is lower; the description still adds real behavior: JPEG/PNG are embedded directly while other formats are re-encoded to PNG, page sizes are A4/Letter/fit, private addresses are refused (SSRF guard), and the result is returned as base64. It does not mention ordering failure behavior or item-count limits.

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?

Five short sentences, front-loaded with the core action, then constraints, then return type. No filler and no redundancy.

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 the return value needn't be spelled out, and the description still covers input forms, conversion behavior, page sizing, and the security constraint. Only margin/orientation semantics and multi-image failure handling are left implicit.

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?

Top-level schema description coverage is 0%, so the description must compensate; it explains the images input (base64 or URL, in order) and the page options, but says nothing about margin or orientation (the latter being a third enum the agent must infer from the schema alone). Enums are largely self-explanatory, keeping this at a baseline 3.

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 and resource: 'Turn images ... into one PDF.' This is clearly distinguishable from siblings like merge_pdf (combines PDFs) or convert_image (single-image format change), so an agent can route correctly without opening the schema.

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 establishes input context (base64 or public URLs, order preserved, page size choices) but never states when to prefer this over merge_pdf, organize_pdf, or convert_image, nor any exclusions beyond refusing private addresses. Usage is implied rather than explicitly routed.

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