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

Annotations are all false, so the description carries the full burden. It adds key behavioral disclosures: inputs are never modified, page sizes are kept as-is (potentially mixed), free tier limit of 5 files, and that the result may indicate mixed sizes. These go beyond the schema and are highly useful for an agent.

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?

Three concise sentences with no wasted words. The purpose is front-loaded, followed by a behavioral caveat and a usage limit. Every sentence earns its place.

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?

The tool is simple, and the schema covers all parameters, including the return link for out_path. The description adds necessary caveats about mixed sizes and free tier limits. No output schema exists, but the return behavior is implied through the out_path schema description, so coverage is adequate.

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%, and each parameter (paths, out_path, overwrite) is already clearly described. The tool description adds no extra parameter semantics beyond what the schema provides, 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 (join) and resource (PDFs) with a clear outcome (into one file). The order requirement is explicit, and the name 'pdf_merge' plus description unambiguously distinguishes it from siblings like pdf_split.

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 clearly implies when to use it (when joining PDFs) but does not explicitly name alternatives or state when not to use it. No exclusion criteria are given, so an agent must infer usage from the clear purpose.

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