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

Annotations already cover idempotency and non-destructiveness. The description adds genuinely useful operational behavior beyond those annotations: it costs one credit per call and returns a temporary download link valid for 15 minutes. It does not mention file-size or processing limits, but no contradiction exists.

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 short and front-loaded with the core purpose. However, 'One credit regardless of how many files' and 'Costs 1 credit per call' are redundant, so not every sentence earns its place.

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 simple one-parameter tool, the description covers purpose, ordering, pricing, and output link expiry. The min/max count is already in the schema, and there is no output schema requiring explanation, so no major contextual gap remains.

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%, and the schema already documents that files are base64-encoded PDFs in order. The description reinforces the order requirement, but does not add substantial new meaning beyond the 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 clearly states it merges 2 to 20 PDF files into one with a specific verb and resource. However, it does not explicitly contrast itself with sibling PDF tools such as split_pdf or images_to_pdf, though its uniqueness is fairly evident.

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?

Usage is implied: call this when several PDFs need to be joined in order. It does not explicitly state when to prefer an alternative or when not to use this tool, but the core use case is reasonably clear from the description.

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