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

Annotations declare readOnlyHint=false, openWorldHint=false, and destructiveHint=false, so the agent knows this is a write operation confined to the tool's environment. The description adds valuable behavioral context: Free tier limit, Pro+ audit trail feature, and the fact that the tool draws or types a signature. It doesn't mention reversibility or permissions, but with annotations covering the safety profile, this is solid.

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?

Compact single sentence with key details front-loaded: action, methods, Pro+ feature, and tier limit. It's efficient but could be slightly more structured, as the category tag at the end feels like metadata rather than description.

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 two-parameter tool with full schema coverage, no output schema, and clear annotations, the description covers the essential: what it does, how to use it, tier constraints, and a distinguishing feature (audit trail). Nothing critical is missing for an agent to invoke it correctly.

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 both parameters are fully documented in the schema. The description adds practical guidance by explaining how to build the 'fields' parameter (use the PDF E-Signature page to draw boxes and paste the value) and notes the 100-placement limit, which goes beyond the schema's technical description.

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?

States a specific verb+resource: placing signature, initial, date, or text fields onto a PDF. It clearly distinguishes itself from sibling tools like esign_prepare and pdf_watermark by naming the exact placement action and the Pro+ audit trail feature.

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?

Implies when to use it (to add signature fields to a PDF) and mentions the Free tier limit of 3 signed documents per month, which is useful context. However, it does not explicitly state when NOT to use it or name alternatives like esign_prepare for a different signing workflow.

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