browser_fill

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

With no annotations, the description carries the full behavioral burden. It does disclose the key behavior of clearing the input before typing, which is consequential and not obvious from the name. However, it does not mention whether the element must be visible, whether the tool waits, or what happens on failure, leaving some 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 compact and well-structured: one purpose sentence, then Args and Returns sections. It is front-loaded with the core action and contains no filler or redundant restatement of the tool name.

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 three-parameter tool with an output schema, the description covers the purpose, all parameter semantics, and the return type sufficiently for an agent to call it correctly. The main gap is lack of usage differentiation from browser_input, but that is already scored under usage guidelines.

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 0%, but the description compensates fully: serialno is tied to list_devices, selector is identified as a CSS selector, and value is described as the text to type. Each parameter gains meaning beyond its bare name and type.

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 first sentence 'Clear an input and type a value into it' states a specific verb and resource, and the selector parameter makes clear this targets a browser input. It is distinguishable from most siblings like mobile_tap or browser_navigate, but it does not differentiate itself from the closely named browser_input, which may sound like the same action.

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 no guidance on when to use browser_fill versus browser_input, browser_click, or mobile_input_text. There are no exclusions, alternative recommendations, or context hints beyond the action itself, so an agent has to infer when this tool is the right choice.

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