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

Without meaningful annotation support, the description carries the burden and does state key behavioral facts: it is free, creates a merged PDF, preserves the given order, and returns a new artifact_id. It does not discuss limits, source immutability, or sync behavior, but for a simple merge operation it is substantially transparent.

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 short and front-loaded with the core action. It earns points for including the alternative tool and return value, but it loses a point for near-duplicate phrasing: 'Join whole PDFs into one file in the order given' and 'Join whole PDFs in order' say essentially the same thing.

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 one-parameter tool with a simple result, the description covers the source list, ordering semantics, output artifact_id, and the key alternative for finer-grained selection. It omits things like file count limits or source existence checks, but these are not necessary for basic 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 coverage is 0%, and the description compensates by explaining that sources is a list of artifact identifiers and that the order of items matters. The phrasing 'list of {artifact_id}' is slightly ambiguous against the schema's object item type, but it still adds essential meaning beyond the empty `additionalProperties` schema.

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 clear verb and resource: 'Join whole PDFs into one file in the order given.' It also distinguishes the tool from compose_pdf by explicitly limiting the operation to whole PDFs rather than page selections.

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 gives explicit guidance on when to use this tool ('whole PDFs', 'in order') and when not to, directing the agent to compose_pdf for page selections. This is more than enough to route an agent correctly among the PDF-manipulation siblings.

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