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carlosphyll

phyll

by carlosphyll
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JavaScript
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fill

Type test data into a text field, finding it by its label or placeholder, and replace its current value. Returns the field and adjacent content for UX auditing.

Instructions

Type a value into a text field, replacing what it held. Find the field by its label, or by its placeholder when it has no label; a label that matches no field is tried as a placeholder. Returns the field typed into and anything that followed. Use obvious test data, never real personal data, passwords or payment details.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
labelNoVisible label of the field, such as Email or Keyword. Part of the label is enough.
valueYesText to type, such as test@example.com. It replaces what the field held.
placeholderNoPlaceholder text of a field that has no label, such as you@example.com.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed3 schema fields changedv0.4.6
    • addedInput schema / properties / label / description
      Added value: +"Visible label of the field, such as Email or Keyword. Part of the label is enough."
    • addedInput schema / properties / placeholder / description
      Added value: +"Placeholder text of a field that has no label, such as you@example.com."
    • addedInput schema / properties / value / description
      Added value: +"Text to type, such as test@example.com. It replaces what the field held."
  2. First observedv0.4.5

TDQS

A4.7/5.0
Behavior5/5

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

With no annotations, the description fully carries the burden. It discloses the replacement behavior, the label/placeholder matching fallback, the return value, and includes a strong safety warning about test data. This exceeds the minimal expectations for a mutation tool without annotations.

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?

Three sentences with zero waste. The main action is front-loaded, and each sentence adds critical information: behavior, field-finding logic, and data safety. Perfectly sized for the tool's complexity.

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 a simple 3-parameter tool with no output schema or annotations, the description covers all necessary aspects: how to identify the target, the overwriting behavior, return information, and safe usage guidance. An agent can invoke this tool correctly without any further clarification.

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?

Schema coverage is 100%, so the baseline is 3. The description adds meaningful semantics by explaining the precedence and fallback between label and placeholder, which is not fully captured in the schema's individual parameter 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?

States a specific verb ('Type') and resource ('text field') with the key behavior of replacing existing content. Clearly distinguishes itself from siblings like click, select, and check, which perform other actions on form elements.

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?

Provides clear context on how to use the tool, including field location by label or placeholder and the fallback order. It does not explicitly name alternatives or exclusion conditions, but the description implies it is for text inputs, which is sufficient given the sibling set.

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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