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ecobrowser MCP server

ecobrowser MCP server

by HaidarESBER
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Local

browser_evaluate

Execute JavaScript expressions in a browser page and retrieve the JSON-serialized result for data extraction.

Instructions

Run a JavaScript EXPRESSION in the page and return its JSON-serialized result (e.g. document.title or [...document.links].length). Not a statement body.

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

Input Schema

NameRequiredDescriptionDefault
jsYesA JS expression to evaluate in the page

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.1

TDQS

A3.8/5.0
Behavior3/5

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

With no annotations, the description carries the full burden. It clarifies the tool evaluates expressions (not statements) and returns JSON-serialized results. However, it does not disclose whether the expression can modify the page or what happens on errors (e.g., thrown exceptions). This is a moderate level of transparency.

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 concise sentence with an illustrative example, efficiently conveying the core functionality without redundancy. Every word serves a 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?

Given no output schema, the description adequately mentions the return format (JSON-serialized). It covers the main use case and constraint (expression vs statement). Minor gaps include error handling and side-effect disclosure, but it is largely complete for a simple read-oriented 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 coverage is 100%, so the baseline is 3. The description adds context with examples of valid expressions, but the parameter description itself ('A JS expression to evaluate in the page') adds little beyond what is already stated in the tool description.

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 evaluates a JavaScript expression and returns JSON-serialized results, with concrete examples like `document.title`. It distinguishes itself from statement execution by explicitly saying 'Not a statement body', which differentiates from potentially similar tools like browser_console.

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 usage for reading dynamic page values, but does not explicitly state when to use this tool versus siblings like browser_console (which may run statements) or browser_read_text (which reads visible text). No alternative or exclusion criteria are provided.

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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