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

Annotations only declare readOnlyHint and openWorldHint; the description adds genuinely new operational context the annotations cannot convey: the return format (finished PDF as base64), the merge ceiling of 10 files, and a per-call price of $0.01 USDC (x402). Those are real behavioral facts. It does not, however, clarify that filling produces a new artifact rather than mutating anything, which would have resolved the mild tension with readOnlyHint.

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 tight sentences with the capability list front-loaded and cost/output last, which is the right order. Every sentence carries information; the 'PDF forms:' lead-in is slightly redundant with the tool name but costs almost nothing.

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?

There is no output schema, and the description does correctly state the return value (base64 PDF), which is the most important gap to close. Still, for a multi-action tool where all 6 parameters are optional, it never explains the parameter-to-action pairing (e.g., `fields` for fill, `urls` for merge, `url` or `pdf_base64` for input), which an agent needs to build a correct call.

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 only 50% across 6 parameters, so the description must compensate. It does partially: it explains the field value types (text, checkboxes, dropdowns) behind `fields` and adds the 'up to 10' limit for `urls` that the schema omits. It says nothing about `url` vs `pdf_base64` as alternative input sources or which parameters apply to which action, so the compensation is incomplete.

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 names concrete verbs and resources: list fillable fields, fill (text, checkboxes, dropdowns), flatten, and merge up to 10 PDFs. An agent immediately knows the capability set. It stops short of differentiating from adjacent siblings like pdf_tools or pdf_to_images, so it is clear but not fully disambiguated.

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 three operating modes (list / fill / merge) are described, which implicitly maps to the `action` parameter and gives some usage signal. However, there is no explicit when-to-use, when-not-to-use, or routing statement versus siblings such as pdf_tools or office_convert, leaving selection to inference.

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