fill_input

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

With no annotations provided, the description carries full responsibility for behavioral disclosure. It reveals the default timeout of 7 seconds, the exception when the element is not found, the clearing-vs-appending behavior for each mode, and that set_value skips key events. This is substantial and useful behavior-level detail.

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 well-structured with a front-loaded purpose sentence followed by a compact argument list. Each line delivers meaningful information, and the mode list is appropriately detailed without being rambling.

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 that an output schema exists and the operation is a single form-field action, the description covers the essential invocation knowledge: target elements, mode behavior, timeout, and failure handling. It does not discuss when not to use the tool, but that is not essential for correctly filling an input.

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?

Since schema description coverage is 0%, the description compensates well: it explains all enum values for mode, clarifies what text does in each mode, and specifies timeout semantics. Only 'selector' lacks explicit elaboration, but its meaning is strongly implied by the tool name and standard conventions.

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 uses a specific verb ('Set the value of') and names the exact target element types ('input, textarea, or contenteditable element'). This clearly distinguishes fill_input from generic sibling actions like click or element_action, even without explicitly naming them.

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 tool's purpose is clear and provides mode-specific usage guidance ('good for sliders and other fast form fills', 'good for when the extra stealth doesn't matter'). However, it does not explicitly enumerate when to prefer a sibling tool such as element_action or run_javascript, so it stops 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.