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

Annotations already indicate the tool is not read-only and not destructive; the description adds meaningful behavioral scope by stating that only non-secret fields are filled and explicitly prohibing secret-type values. This goes beyond what the annotations alone communicate and helps set accurate expectations for a mutating form-fill operation.

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 two tight sentences with no filler. The core action is front-loaded, and the exclusion list is compact yet comprehensive. Every word earns its place.

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?

Given the small parameter count, full schema coverage, and existing output schema, the description plus schema are sufficient for correct invocation. It lacks some context about when to prefer this tool over siblings, but that gap is captured in usage_guidelines rather than making the tool description incomplete.

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 description coverage is 100%, so the input schema already fully documents sessionId and the fields map. The description largely repeats the schema's wording ('label/placeholder/name', 'non-secret value') without adding new parameter-level meaning, keeping this at the baseline.

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 clearly states a specific action ('Fill') and resource ('non-secret form fields') and further specifies how fields are identified ('label/placeholder/name'). It also draws a clear boundary by excluding passwords, OTPs, and Companies House auth codes, which helps distinguish it from related sibling tools even though no sibling is explicitly named.

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 implies usage on a live browser session to fill visible form fields, and the 'Never passwords, OTPs, or Companies House auth codes' statement provides a clear negative constraint. However, it does not explicitly compare with alternatives such as draft_form_answers, prepare_portal_fill, or list_fillable_fields, leaving some routing ambiguity.

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