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

Annotations already declare readOnly, idempotent and non-destructive, and the description adds substantial context beyond them: password-protected PDFs are rejected, form fields are flattened, output is a ZIP capped at 50 PDFs, individual links appear only when there are 10 parts or fewer, and page counts are verified. These are non-obvious side effects and limits an agent could not infer from the annotations.

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?

Single dense paragraph that front-loads the trigger conditions before the mechanics, with no filler sentences. It is on the long side, but each clause carries distinct information about inputs, output limits, or restrictions.

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?

An output schema exists, yet the description still summarizes the return shape (ZIP plus conditional links) and the 50-part cap, which is the key operational limit. Combined with the mode exclusivity, failure mode (encrypted PDFs), and the merge_pdfs alternative, nothing an agent needs to invoke it correctly is missing.

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 100%, so the baseline is 3, but the description adds a genuine constraint the schema does not encode: the caller supplies 'one of' ranges, every_n_pages, or each_page, i.e. mutual exclusivity, plus a worked example of the ranges syntax. It does not spell out what happens if multiple modes are passed or how 'end' resolves beyond the example.

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 ('split a PDF') and enumerates the concrete output shapes: page ranges, groups of N pages, one file per page. It explicitly distinguishes itself from the sibling merge_pdfs, so an agent can choose without opening either schema.

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?

Opens with explicit user-intent triggers ('when the user wants to split a PDF into several files, break a PDF into parts, extract page ranges...') and closes with an explicit exclusion naming the alternative: 'Do not use for combining several PDFs (use merge_pdfs).' Both the when and the when-not are covered.

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