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

Annotations only cover the safety profile (readOnly, idempotent, non-destructive). The description adds materially more: the credit cost formula (ceil(pages written / 20), min 1), the 1 MiB inline output cap, and the exact return shape (part_01.pdf vs split.zip with meta {parts, page_count}). None of that is available elsewhere.

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?

Information-dense and front-loaded with the core action, with cost and output details following in priority order. The output-naming clause ('part_01.pdf when there is one part, otherwise split.zip holding part_01.pdf ...') is a bit run-on, but every sentence carries distinct, non-duplicated information.

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 carries the return-value burden and does so fully: format, MIME type, size limit, file naming, and meta contents. Input formats, cost model, and both splitting modes are all covered, leaving nothing an agent needs before calling.

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%, so all three parameters are already documented. The description's input-format note (base64, data: URI, {"url": ...}) and range syntax example largely restate the schema, so the baseline 3 applies.

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+resource (split a PDF) plus two distinct modes (page ranges or every N pages) and the two possible outputs (single PDF or zip). This distinguishes it clearly from pdf_merge (combining) and pdf_info (inspecting) without needing to open any 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?

Gives clear context for the two operating modes: 'by page ranges such as "1-2,5-" or every N pages'. It does not, however, explicitly state when NOT to use it (e.g. use pdf_merge to combine, pdf_info to inspect), so the routing guidance is implicit rather than explicit.

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