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

Annotations already declare readOnly=false, destructive=false, and idempotent=false, and the description does not contradict them. It adds genuinely useful context beyond annotations: a size-dependent return path (inline PDF vs. metadata plus a pollable job reference), which is a real async pattern an agent must know about.

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?

Two tightly written sentences with the core action front-loaded and the return semantics second. No filler or redundancy.

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 no output schema, the description correctly carries the burden of explaining return values, and it does so for both the inline and async paths. It is slightly incomplete on operational constraints (per-file size ceiling, total limits, failure modes), but covers what an agent needs to invoke and consume the result.

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?

The single parameter has 100% schema description coverage, so the schema already explains that inputs are base64 PDFs merged in order, with min/max item bounds. The description adds nothing about parameter format or the 11MB per-file limit, so baseline 3 is appropriate.

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 ('Merge two or more PDFs into a single document'), which is unambiguous and inherently distinct from the inverse sibling pdf_split. It does not explicitly name or differentiate against any sibling, but the verb-resource pairing leaves little room for confusion.

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?

There is no statement of when to use this versus alternatives like pdf_compress or pdf_split, nor any prerequisites (e.g., access requirements or that inputs must be valid PDFs). The only routing hint is that job references can be polled via job_status, which is output behavior rather than tool-selection guidance.

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