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

Beyond the annotations, the description discloses the credit cost ('Costs 1 credit per call'), the temporary download link behavior ('valid 15 minutes'), and the flatten side effect ('make the result non-editable'). These are meaningful operational details not present in the annotations or schema.

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 compact and front-loaded with the core behavior, followed by cost and output-link instructions. The first sentence slightly repeats the title, but every other sentence adds necessary information without padding.

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 compensates by specifying the return value ('temporary download link valid 15 minutes') and instructing the agent to include it in the reply. It covers the main behavioral modes and cost, leaving little ambiguity for a tool of this complexity.

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 value by explaining the relationship between `data` and `inspect` ('Without `data` (or with inspect=true) it returns the list of fields') and by clarifying the purpose of `flatten` ('make the result non-editable'). This goes beyond the schema's individual parameter descriptions.

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 specific verb and resource: it 'Fills the fields of an existing PDF form (AcroForm) with the values in `data`.' It also clearly distinguishes the field-listing mode ('Without `data` (or with inspect=true) it returns the list of fields'), which separates it from sibling PDF tools like merge_pdfs or extract_pdf_text.

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 clear context on when to use the tool and how to switch modes: pass `data` to fill, omit it or set `inspect=true` to list fields. It does not explicitly name alternative tools or state when not to use it, but the mode guidance is practical and sufficient for an agent.

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