@nxavis/agent-browser-mcp

by softallice

Overview Schema Source Related Servers Discussions Admin

TypeScript

Local

browser_evaluate

Run JavaScript code directly in an active browser session to automate actions, test features, or extract page data.

Instructions

Execute JavaScript code in the browser context

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

Input Schema

Name	Required	Description	Default
`script`	Yes	JavaScript code to execute
`sessionId`	No	Browser session ID

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.1Aug 2, 2026

TDQS

B3.1/5.0

Behavior2/5

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It fails to mention potential side effects (e.g., page state changes), return values, session requirements, or whether the code runs in the main frame or isolated context. This is a significant gap for a powerful execution tool.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness3/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single sentence, which is concise and front-loaded with the core action. However, it is underspecified, delivering no context about prerequisites, side effects, or when to use the tool. It is concise but not adequately informative.

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

Completeness1/5

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

Given the complexity of the tool (arbitrary JavaScript execution), the lack of annotations, and no output schema, the description is severely incomplete. It does not cover return values, errors, security implications, or how the sessionId affects execution. This is insufficient for an agent to safely and effectively use the 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?

The schema already provides clear descriptions for both parameters (script and sessionId), covering 100% of them. The tool description adds no additional meaning about parameter usage, formats, or constraints beyond what the schema states.

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 executes JavaScript code in the browser context, using a specific verb ('execute') and a distinct resource ('JavaScript code'). It differentiates itself from sibling browser_* tools by focusing on arbitrary code execution rather than predefined actions.

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

Usage Guidelines3/5

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

The description implies this tool is for running custom JavaScript, but it does not explicitly say when to use it over the sibling tools (e.g., for complex interactions not covered by click/fill). No exclusions or alternative recommendations are provided.

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