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

Beyond the annotations (readOnly=false, destructive=false), the description transparently explains the mutation (combining PDFs), the return type (file_id), and the time-limited download URL ('~1h download URL'). This goes beyond the minimal annotation coverage and gives the agent a clear model of the tool's behavior.

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. The first states the core function, and the second clarifies inputs and outputs. There is no redundant or extraneous information, making it easy to parse.

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?

Given the single parameter and lack of output schema, the description covers all necessary information: inputs, output format, ordering, and the chaining capability. It is complete for an agent to invoke the tool correctly.

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 only parameter 'pdfs' is fully described in both the schema and the description: it must contain 2+ items, each being a file_id or base64 PDF. The description and schema are consistent, leaving no ambiguity about what values are accepted.

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 clearly states the tool's action: 'Combine 2+ PDFs into a single PDF, in the order given.' It also specifies input types (file_ids or base64 PDFs) and output format (file_id and download URL), leaving no ambiguity about the tool's purpose.

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 provides usage context by specifying that inputs can be 'file_ids (from prior tools) or base64 PDFs' and that the output file_id is 'for chaining'. It does not explicitly contrast with sibling PDF tools (e.g., split, rotate), but the merge purpose is so distinct that an agent can reliably select it without further guidance.

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