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

Annotations already declare that this is a non-read-only, non-destructive, non-idempotent operation. The description adds useful behavior beyond that by noting the output includes bookmarks named after each part and that input ordering is respected. It does not describe permissions, limits, or error behavior, so a 3 is appropriate given annotation coverage.

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 two concise sentences with the core action front-loaded and the ordering/bookmark details immediately following. Every sentence adds useful information without repetition or filler.

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?

With an output schema present and annotations covering safety semantics, the description supplies the key behavioral details an agent needs: merge ordering and bookmark output. It does not mention edge cases such as supplying no files or mixed-source constraints, but it is otherwise complete for correct invocation.

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%, so the baseline is 3. The description adds important cross-parameter semantics that the schema does not: when multiple input arrays are supplied, they are combined in the fixed order file_ids, then files, then file_urls. This prevents ambiguity for an agent deciding how to pass inputs.

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 states a specific verb and resource: "Join PDFs into one." It also clarifies the resulting ordering and bookmark behavior, making the tool's function immediately clear and distinguishable from siblings like split_pdf or compress_pdf.

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 when to use the tool (when PDFs need to be joined) but does not explicitly state when to choose it over alternatives such as split_pdf, create_pdf, or edit_pages. No exclusions or prerequisites are given, leaving usage guidance at an implied level.

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