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

With only destructiveHint=true available in annotations, the description carries real added burden and delivers: it discloses that the call is BILLED and that the returned FileUrl has a ~24h lifetime. It still omits cost magnitude, credit/rate-limit behavior, and whether source PDFs are retained, which prevents a 5.

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 short clauses front-load the operation, then the return, then billing and the API route. No sentence is wasted and nothing requires reading ahead to understand the core action.

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 an 8-parameter tool with nested objects and no output schema, the description covers the essentials an agent needs to call it correctly: ordered URL input, the FileUrl return with its expiry, and the billing implication. Remaining gaps (custom storage, binary output, options pass-through) are fully covered by the 100%-coverage schema, so the definition is close to complete.

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 every one of the 8 parameters is already documented in the schema, including the ordering semantics and the storage/options nesting. The description only restates 'URLs, in order' and adds nothing about options, storage, useCustomStorage, or output_binary, 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?

The description gives a specific verb and resource ('Merge several existing PDFs ... into a single PDF') and immediately names the input form (URLs, ordered) and the underlying engine endpoint. An agent can distinguish it at a glance from siblings like api2pdf_compress_pdf or api2pdf_extract_pages.

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?

It states the input shape and ordering constraint, which implies when the tool applies, but never names an alternative or a when-not condition (e.g. when to use extract_pages or compress_pdf instead). Usage context is implied rather than explicit.

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