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

Annotations already declare readOnlyHint=true, and the description adds genuine operational context beyond that: merge order is preserved ('순서대로'), only PDF inputs are accepted, and each call costs 2 points. This does not contradict the annotations since merging returns a new file without mutating the inputs. The only gap is the unspecified return delivery format (URL vs. binary).

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?

Four short sentences with the core action front-loaded in both English and Korean. The bilingual restatement is mildly redundant, but the Korean variant contributes unique details (ordering, return behavior) and the cost note is compact and useful.

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 low-complexity 2-parameter tool with 100% schema coverage, readOnly annotation, and a clear purpose, the description covers the essentials including input constraints and cost. The main omission is the output format since no output schema exists, but the statement '하나의 PDF 파일로 합쳐 반환합니다' partially addresses the return value.

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%, with both parameters fully documented as downloadable https URLs accepting application/pdf up to 25MB. The description's format restriction largely restates the schema, so it adds little parameter meaning beyond the 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?

States a specific verb+resource+outcome: 'Merge two PDF files into one,' reinforced by the Korean '두 개의 PDF 파일을 순서대로 하나의 PDF 파일로 합쳐 반환합니다.' This is unambiguously distinguishable from sibling converters (pdf_to_docx, pdf_to_image, docx_to_pdf) and clearly describes the combining operation.

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 by the purpose statement (combine two PDFs → call pdf_merge), and constraints like 'PDF 형식의 파일만 허용됩니다' (only PDF format allowed) and the 2-point cost give partial applicability guidance. However, no explicit when/when-not conditions or alternative tools are named, so routing decisions are left to inference.

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