browser_fill

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

With no annotations provided, the description carries the full burden of behavioral disclosure, yet it only states the verb 'fill'. It does not disclose that filling typically replaces existing field content, whether the tool waits or scrolls, how timeouts behave, or the iframe behavior represented by frameSelector in the schema. It is not misleading, but it is minimally transparent for a mutation tool.

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?

A single 11-word sentence that front-loads the verb and targeting scope with no filler words. Efficient structure, though the terseness trades away behavioral detail that is penalized in other dimensions.

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 five parameters, two mutually exclusive targeting modes, optional iframe targeting, a timeout, and zero annotations or output schema, this description is thin. It omits the frameSelector capability, text/timeout semantics, and any distinction from browser_type or browser_fill_form. An agent could infer much from the schema, but the description alone leaves significant gaps.

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 60% (ref, selector, and frameSelector are documented; text and timeout are not). The description adds marginal value by confirming that refs originate from browser_snapshot and that targeting is via CSS selector or aria ref, but the required text parameter and timeout remain undefined in both the description and schema. 'Fill an input' loosely implies text is the content, which partially compensates.

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 names a specific verb ('fill') and resource ('an input') and identifies the two targeting mechanisms (CSS selector or aria ref from browser_snapshot). It is clear at a glance, but it does not explicitly differentiate from closely related siblings such as browser_type, browser_fill_form, or browser_iframe_fill.

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 only usage cue is 'aria ref from browser_snapshot', which weakly implies a snapshot should be taken first. There is no guidance on when to choose this over browser_type (keystroke simulation), browser_fill_form, or browser_iframe_fill, and no exclusions or preconditions are stated.

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