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fill

Fills input fields, textareas, or contenteditable elements by CSS selector. Automatically descends into wrapper elements to find a fillable target.

Instructions

fill an input/textarea/contenteditable; if the selector matches a wrapper, descends up to 4 levels to a unique fillable descendant (errors if zero or multiple)

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "selector": "<selector>",
      "value": "<value>"
    },
    "name": "fill"
  }
}

Input Schema

Name	Required	Description	Default
`selector`	Yes	CSS selector for input field or its wrapper. Supports 'testid:NAME' and 'dialog::SELECTOR' (scopes to the topmost open dialog/sheet).
`value`	Yes	Value to fill

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.13.0May 11, 2026

TDQS

A4.5/5.0

Behavior5/5

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

The description discloses critical behaviors beyond annotations: it describes the wrapper descent logic (up to 4 levels), error conditions for zero or multiple fillable descendants, and the supported element types. No contradiction with annotations (readOnlyHint=false, idempotentHint=false).

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, well-structured sentence that front-loads the core purpose ('fill an input/textarea/contenteditable') and appends essential behavioral details. Every phrase earns its place, with zero wasted words.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the low complexity (2 parameters, no output schema, no nested objects), the description is fully adequate. It covers the core action, target elements, wrapper handling, and error conditions. No missing details are needed for correct agent usage.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so baseline is 3. The description adds behavioral context for the 'selector' parameter (wrapper descent) but does not add meaning beyond the schema for the 'value' parameter. While helpful, it doesn't significantly elevate parameter understanding beyond what the schema already provides.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states 'fill an input/textarea/contenteditable', specifying the verb and resource types. It distinguishes from siblings like 'click', 'select', and 'press_key' by focusing on filling form fields. The additional detail about wrappers and descent behavior further clarifies its purpose.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies usage for filling text inputs and handles wrapper selectors with a descent strategy. While it doesn't explicitly list alternatives, the concise phrasing and context make it clear when to use this tool versus siblings (e.g., use 'fill' for text, 'click' for buttons). A small deduction for missing explicit when-not-to-use guidance.

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