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playwright-mcp-server

playwright-mcp-server

by doucej
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Local

fill

Set the value of an input or textarea on a web page, replacing any existing content. Use CSS or XPath selectors to target the element.

Instructions

Set the value of an input or textarea, replacing any existing content.

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

NameRequiredDescriptionDefault
valueYesNew value to fill in.
selectorYesCSS or XPath selector.

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv1.0.0

TDQS

A4.2/5.0
Behavior4/5

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

No annotations are provided, so the description carries the full burden. It discloses the key behavioral trait that it replaces any existing content, which is essential for the 'fill' operation. It does not cover event triggering or visibility requirements, but given the tool's simplicity, this is adequate.

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, front-loaded sentence that states the purpose and key behavior with no redundant words. Every part earns its place.

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

Completeness4/5

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

For a simple two-parameter tool with clear schema descriptions, the description is sufficiently complete. It lacks an output schema but that is not necessary for a fill operation that likely returns nothing or a simple status.

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?

The input schema provides full 100% coverage with clear descriptions for both 'value' and 'selector'. The description adds a behavioral note about replacement but does not meaningfully extend the parameter semantics beyond the schema.

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 the tool sets the value of an input or textarea, replacing existing content. This specific verb+resource pairing distinguishes it from siblings like 'type' (which simulates typing) and 'select_option' (for selects).

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 makes clear what the tool does and implies it is for directly setting values, but it does not explicitly name alternatives or when-not-to-use scenarios. Since the context is clear, it earns a 4 rather than a 3.

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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