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browser-mcp-cdp

browser-mcp-cdp

by zhiqi-li
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Local

browser_fill

Set the value of a form element (input, textarea, or select) using a CSS selector. Enables automated form filling in a real Chrome browser with profile isolation.

Instructions

Set the value of an input, textarea, or select element matched by a CSS selector.

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>",
      "text": "<text>"
    },
    "name": "browser_fill"
  }
}

Input Schema

NameRequiredDescriptionDefault
textYesValue to set
selectorYesCSS selector for the form element

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.2

TDQS

B3.4/5.0
Behavior2/5

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

With no annotations, the description fully carries the burden but does not disclose important behavioral traits such as what happens if the element is not found, whether events are triggered, whether existing values are cleared, or whether it works on contenteditable elements. This is insufficient for an agent to 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?

The description is a single sentence that is direct and free of unnecessary words. It efficiently communicates the tool's purpose.

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 tool with two required parameters and no output schema, the description is adequate. It explains the action and element types. However, it could mention error handling or edge cases (e.g., non-existent selector) but is otherwise complete for typical use.

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 description coverage is 100% with both parameters documented ('CSS selector for the form element' and 'Value to set'). The description adds the context that it works on form elements, but this is already implied in the schema descriptions. It does not add significant new meaning 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 explicitly states the action ('Set the value'), the target elements ('input, textarea, or select element'), and the method ('matched by a CSS selector'). This clearly distinguishes it from sibling tools like browser_click (clicking) and browser_get_text (reading).

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

Usage Guidelines2/5

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

No guidance is provided on when to use this tool vs alternatives (e.g., browser_evaluate for JavaScript injection) or when not to use it (e.g., for non-form elements). The description only states the basic function without usage context.

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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