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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint, so the safety profile is covered. The description adds genuinely useful behavioral detail beyond that: private/local addresses are refused (SSRF guard) and the result is returned as base64, which tells the agent not to expect a URL or file handle.

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, front-loaded with the action, then input forms, then a constraint, then the return format. Every sentence carries information; the only mild redundancy is repeating the private-address refusal that the schema also states.

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 and the description still names the return format (base64 PDF), covering both input sourcing and output shape. It is nearly complete for a modest tool, with the main omissions being the file-count limits and that page ranges apply per input file rather than globally.

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 reported as 0%, so the description must carry parameter meaning. It explains the two source modes (base64 or public URL) and the page-range syntax ('1-3,5'), which is the core of the files array, but it omits the 10 MB decoded cap, the 25-file maximum and 2-file minimum, and the name/filename/mimeType fields.

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: 'Combine PDF files', which is unambiguous against siblings like split_pdf, compress_pdf, and organize_pdf. It does not explicitly name or differentiate itself from those siblings, so it stops short of a 5.

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 verb and the note on file sources, but there is no statement of when to prefer this over organize_pdf or split_pdf, or any prerequisite/ordering guidance. An agent must infer the use case.

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