real-browser-mcp

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browser_evaluate

Execute JavaScript in a real browser to query DOM elements, read page state, or perform custom operations within existing sessions.

Instructions

Execute JavaScript in the page and return the result. Use for DOM queries, reading page state, or any operation not covered by other tools.

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": {
      "expression": "<expression>"
    },
    "name": "browser_evaluate"
  }
}

Input Schema

Name	Required	Description	Default
`expression`	Yes	JavaScript expression or code to evaluate in the page context

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.2.0Mar 10, 2026

TDQS

A3.9/5.0

Behavior3/5

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

With no annotations provided, the description carries the full burden. It discloses the core behavior (executing JavaScript and returning results) and hints at use cases, but lacks details on permissions, error handling, execution context (e.g., sandboxing), or side effects like potential page modifications.

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 front-loaded with the core purpose in the first sentence, followed by usage guidance, with no wasted words. Both sentences earn their place by clarifying intent and application.

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

Completeness3/5

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

Given the tool's complexity (executing arbitrary JavaScript in a browser context) and lack of annotations or output schema, the description is adequate but incomplete. It covers purpose and usage but omits critical behavioral details like safety, return formats, or error conditions, which are essential for such a powerful tool.

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%, so the schema already documents the 'expression' parameter fully. The description adds no additional meaning beyond what the schema provides, such as examples or constraints, resulting in the baseline score.

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 specific action ('Execute JavaScript in the page') and the resource ('page'), distinguishing it from siblings like browser_click or browser_navigate by focusing on code evaluation rather than UI interaction or navigation.

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?

It provides clear context for when to use this tool ('for DOM queries, reading page state, or any operation not covered by other tools'), which helps differentiate it from alternatives. However, it does not explicitly state when not to use it or name specific sibling tools as alternatives.

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