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

Annotations already declare readOnlyHint=true; the description adds extra constraints: only PDF files are allowed, order is preserved, and a per-call cost of 2 points applies. These go beyond the annotations and provide useful operational behavior, with no contradiction.

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 very concise, with an English lead sentence followed by a Korean equivalent that adds nuance (ordering, return behavior). It includes the cost note without fluff, making every word meaningful.

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 two-parameter merge tool with no output schema, the description covers key aspects: merging behavior, order, and format restriction. It does not describe the return format (e.g., URL) or error handling, but given the simplicity and 100% schema coverage, it is sufficiently complete.

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% with each parameter documented as a downloadable https URL with format and size limits. The description adds the important semantic that files are merged in the order of pdf_url_1 then pdf_url_2, which the schema alone does not convey.

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 'Merge' and clearly states the resource (two PDF files) and the outcome (one PDF). It is easily distinguished from sibling tools like pdf_to_docx or set_watermark, which serve different purposes.

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 implies usage by stating it merges two PDFs in order and only accepts PDF format. It does not explicitly name alternatives or exclusion scenarios, but the sibling tool list makes the use case clear. The cost note adds practical context.

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