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

Beyond the annotations, the description reveals load-bearing operational behavior: the tool is asynchronous (returns a job_id to poll every ~20 seconds), billed with a free tier, supports retention modes, and can delete source/output documents after 60-70 minutes. This is exactly the kind of context that annotations do not provide.

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 core purpose is front-loaded, and every subsequent sentence earns its place by adding parameter semantics or operational details. For an 8-parameter tool with no schema descriptions, this length is justified and there is no filler or repetition.

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?

Even though an output schema exists, the description still covers the essential workflow: context ingestion, form selection, policy choice, job polling, billing consequences, and retention behavior. An agent has enough information to invoke the tool correctly and interpret what happens next.

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?

The schema has 0% description coverage, yet the description compensates thoroughly: it defines policy values (safe vs strict confidence thresholds), accepted context_urls file types, form-source alternatives, and retention semantics. Each parameter name is given practical meaning beyond its raw schema definition.

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 opens with a specific action, 'Fill a PDF form using facts found in supporting documents,' and immediately names the context sources that distinguish this tool from siblings like fill_form or fill_batch. It also explains the different form-selection modes (form_id, pdf_url/pdf_base64, library), leaving no ambiguity about the tool's core purpose.

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 clearly establishes when to use this tool: when answers should be read from context_text and/or context_urls, and it gives concrete rules for choosing between form sources. It does not explicitly name fill_form or fill_batch as alternatives or state when not to use them, so it stops short of full exclusion guidance.

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