Fill Form (AcroForm)

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

Annotations already mark this as a non-read-only, idempotent, non-destructive operation. The description adds valuable behavior beyond that: flattening breaks PDF/UA conformance on tagged PDFs and requires allowBreakingTags: true, CJK values need a font, and the error response lists all field names/types when given an unknown field. It does not mention signature-breaking behavior (covered in the schema) or the base64 return option (also in schema), but it covers the most consequential side effects and requirements.

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 a compact paragraph of four sentences, each earning its place: main purpose, field-discovery tip, CJK requirement, and flatten side-effect warning. It is front-loaded with the core action and keeps the most important caveats early. No redundant or filler content.

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 a tool with 8 parameters, nested objects, and no output schema, the description covers the essential behavioral and usage context an agent needs: how to discover field names, font requirements for non-Latin text, the flattening caveat, and the unsupported XFA case. Output format and signature-breaking behavior are already documented in the schema, so they do not need repetition. The description is complete for successful invocation.

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 already describes all 8 parameters with 100% coverage, so the baseline is 3. The description enhances this by explaining cross-parameter dependencies (CJK requires fontPath or the PDF_WRITER_FONT env var, flatten on a tagged PDF requires allowBreakingTags), and it explains the field-naming trick that affects how the fields parameter is used. This goes beyond simply restating the schema and gives the agent practical guidance on parameter usage.

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 verb-resource pair ('Fill field values into an existing PDF's interactive form (AcroForm)') and explicitly scopes the tool to AcroForm, distinguishing it from the sibling flatten_form and other PDF tools. It also notes XFA forms are unsupported, further clarifying its domain. An agent can unambiguously identify this as the tool for populating interactive form fields.

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 practical guidance: a trick for discovering field names by passing a nonexistent one, a prerequisite for CJK values (fontPath or env var), and a clear exclusion (XFA not supported). It does not explicitly point to the sibling flatten_form for flatten-only workflows, and it does not contrast with other form-related tools, but the scope and exclusions are sufficient for most selection decisions.

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