browser_fill

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

No annotations are provided, and the description does not disclose behavioral details such as whether it clears existing values, triggers input/change events, works on contenteditable elements, or handles special characters. 'More robust' is vague and leaves significant behavioral ambiguity.

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 single, front-loaded sentence with zero filler words. Every word earns its place, and the comparative clause adds value without bloating the structure.

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 simple two-parameter tool, the description is minimally sufficient, but it lacks key context such as behavior with existing values, event triggering, or differences from browser_type that are not covered elsewhere. The absence of annotations and output schema increases the burden on the description, which is not fully met.

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%: both parameters (value and selector) have descriptions. The tool description does not add any additional semantic meaning beyond what the schema already provides, so the baseline of 3 applies.

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 is concise and specific: 'Fill form field with value' clearly identifies the action (fill) and resource (form field). It also distinguishes itself from sibling tool 'browser_type' by adding 'more robust than type', which differentiates its purpose without ambiguity.

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 phrase 'more robust than type' provides a comparative guideline, implying use this tool when a more reliable fill is needed over browser_type. However, it does not explicitly state when NOT to use it or mention other alternatives, so it falls short of a 5.

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