Fills an input field matched by a selector, replacing the entire existing value in one action. Use it instead of typing keystrokes when you need to overwrite a field.
Fill an input field matched by selector; fill replaces the whole value (browser_type appends keystrokes).
| Name | Required | Description | Default |
|---|---|---|---|
| value | No | ||
| selector | No |
Changes observed during successful MCP inspections.
v0.1.2Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the whole burden. It does disclose one genuinely useful behavioral trait — that the existing value is fully replaced rather than appended — but says nothing about failure behavior, auto-waiting/retries, whether input/change events are dispatched, or what a successful call returns.
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 sentence with zero waste: the action and its scoping semantics come first, the sibling differentiation second. Nothing to trim and nothing buried.
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?
The tool is simple and has no output schema or annotations to reconcile, but with 0% schema coverage and no required-parameter marking in the schema, the description should still state the selector format and at least hint at failure behavior. It is adequate for the happy path only.
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%, so the two parameters are undocumented structurally; the description only partially compensates by implying selector identifies the target element and value is the replacement text. No detail on selector syntax (CSS vs XPath), whether value is optional, or why 0 params are marked required.
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?
States a specific verb+resource ("Fill an input field matched by selector") and immediately contrasts with the sibling browser_type by semantics (replace vs append). An agent can distinguish browser_fill from browser_type without consulting either schema.
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?
Explicitly names the alternative browser_type and the condition that selects it: fill replaces the whole value, while browser_type appends keystrokes. Missing is any guidance on prerequisites or edge cases (element not found, non-editable elements, whether it waits for the element), so it stops just short of full when/when-not coverage.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.