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pony-browser-mcp

pony-browser-mcp

by pssrh
OverviewSchemaSourceRelated ServersDiscussionsAdmin
JavaScript
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browser_fill

Fill form inputs using CSS or text-based selectors, with auto-scroll and focus, even on sites with strict CSP.

Instructions

Fill a form input field with a value. Supports CSS selectors AND text-based selectors. Auto-scrolls and focuses the element. Works on CSP-strict sites via Chrome Debugger API. For date inputs use browser_set_date, for autocomplete/combobox use browser_set_combobox.

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": "browser_fill"
  }
}

Input Schema

NameRequiredDescriptionDefault
valueYesValue to fill in
selectorYesCSS selector or text selector for the input field

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv1.0.1

TDQS

A4.4/5.0
Behavior4/5

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

With no annotations, the description carries the full burden and it delivers meaningful behavior: auto-scrolling, focusing the element, and working on CSP-strict sites via the Chrome Debugger API. It doesn't mention potential side effects like overwriting existing values or triggering events, but the disclosed traits go well beyond a minimal description.

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 efficient: a one-line purpose, two capability notes, and a two-item routing sentence. Every sentence earns its place, and the core action is front-loaded before alternatives.

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 no output schema, the description covers the essential use context: why it exists, what behaviors it performs, technical limitations it handles (CSP), and alternatives for edge cases. Minor gaps like error behavior or event triggering are not critical for a fill operation, so this is almost fully complete.

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%, with both 'selector' and 'value' already documented. The description repeats the selectors info but adds little beyond what the schema states. Baseline 3 applies because the schema does the heavy lifting and the description does not materially enhance parameter understanding.

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 clear verb and resource: 'Fill a form input field with a value.' It explicitly differentiates from nearby siblings by naming browser_set_date for date inputs and browser_set_combobox for autocomplete/combobox controls, so an agent can tell them apart without opening schemas.

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?

The description provides explicit routing: 'For date inputs use browser_set_date, for autocomplete/combobox use browser_set_combobox.' It also clarifies the accepted selector types (CSS and text-based), helping the agent decide when this tool is appropriate. This is direct when-to-use guidance with named alternatives.

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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