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DB-25

arc-control-mcp

Fill Field

fill

Fill input, textarea, or contenteditable elements with a specified value. Use CSS selector or matching visible text; native setter fires input/change events for React, and errors on non-fillable targets.

Instructions

Set the value of an input, textarea or contenteditable. Uses the native setter and fires input and change, so React and similar frameworks register it. Fails with an error naming the tag when the target cannot be filled: a heading or other non-input, a disabled or readonly field, or a (use select_option for those). "text=Label" matches on visible text as a substring, with exact matches ranked first, so a short label also matches longer ones. Check the returned "matches" count, and pass exact when it is above 1.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
nthNoWhich match to fill, 0-based
exactNoFor "text=" selectors, require the whole trimmed text to equal the label instead of containing it. No effect on CSS selectors.
valueYesValue to set
submitNoPress Enter and request form submit afterwards. The tab usually navigates, so follow with wait_for_load: the returned tab snapshot may predate the navigation, and urlBefore reports the url from just before the key press.
tab_idNoArc tab id from list_tabs. Omit to use this agent's current tab, falling back to whatever tab is active in Arc.
verboseNoInclude the bulky element rect and longer attribute values
selectorYesCSS selector, or "text=Some label" to match on visible text (substring, exact matches ranked first)
Install Server

TDQS

A4.9/5.0
Behavior5/5

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

The description discloses that it uses the native setter, fires input/change events so React registers the change, and fails with an error naming the tag. These behavioral details go well beyond the readOnlyHint/destructiveHint annotations and help the agent predict side effects.

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?

Every sentence carries operational weight: the action, the framework-compatibility mechanism, the failure modes, and the selector-matching rule. It is front-loaded with the primary purpose and contains no filler.

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?

For a 7-parameter mutation tool with no output schema, the description covers the main edge cases, selector ambiguity, and failure behavior, while the schema covers parameter defaults. Nothing needed for correct invocation is missing.

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

Parameters4/5

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

The schema already documents all 7 parameters at 100% coverage, so the baseline is 3. The description adds practical matching semantics (substring matching with exact matches ranked first) and a concrete ambiguity-resolution instruction that goes beyond the schema's field descriptions.

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 opens with a specific verb and resource ('Set the value of an input, textarea or contenteditable') and immediately distinguishes the tool from siblings by listing what it cannot fill, e.g. '<select> (use select_option for those)'.

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

Usage Guidelines5/5

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

It explicitly names the alternative for selects, warns when filling will fail (non-inputs, disabled/readonly fields), and provides a decision rule for ambiguous label matches: check the returned 'matches' count and pass exact when above 1.

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

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