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

With no annotations provided, the description must disclose behavioral traits. It implies a read-only operation ('count and report') but does not explicitly state safety, potential side effects, failure modes (e.g., invalid URL handling), or requirements like network access. The description adds minimal context beyond the obvious, leaving significant ambiguity for an agent.

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 description is a single sentence with no wasted words, front-loading the core action. However, it omits necessary context like parameter details and error handling, making it concise but under-specified. Still, it is appropriately short for a simple tool, so it earns a 4.

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?

Given the tool has only one parameter, no annotations, and no output schema, the description should compensate with richer context. It fails to specify input requirements, output format (beyond 'page size'), or error behavior. The description is too sparse to fully support agent decision-making, resulting in an incomplete picture.

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?

The schema defines a single parameter 'url' with zero type or description, and schema description coverage is 0%. The description only mentions 'by URL', giving no details on format, requiredness, or usage. This is insufficient for the agent to construct a valid invocation, especially since the schema marks it as not required.

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 uses a specific verb ('Count', 'report') and resource ('a PDF by URL'), clearly stating what the tool does. It distinguishes from siblings like merge_pdf or split_pdf by focusing solely on page count and page sizes, which is a unique capability among the listed tools.

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 provides no guidance on when to use this tool versus alternatives like pdf_rotate or pdf_watermark. It does not suggest exclusions, prerequisites, or alternative tools. The agent is left to infer usage solely from the purpose, which is not sufficient given the large sibling list.

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