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by office233
OverviewSchemaSourceRelated ServersDiscussionsAdmin
JavaScript
Local

browser_evaluate

Destructive

Execute JavaScript in the current page by passing an expression or a function body with a return statement to read or change DOM values.

Instructions

Run JavaScript in the page. Pass an expression ("document.title") or a function body using return.

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

NameRequiredDescriptionDefault
scriptYes

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv1.1.0

TDQS

B3.2/5.0
Behavior2/5

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

Annotations already declare destructiveHint=true, readOnlyHint=false and openWorldHint=true, so the risk profile is covered by structured data. The description adds nothing behavioral beyond that: it says nothing about execution context/privileges, sandboxing, timeouts, or error behavior for arbitrary code execution.

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?

Two short sentences, front-loaded with the action and then the argument format. No filler.

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?

With one parameter and annotations covering safety, the description is nearly sufficient. But there is no output schema, so the return value (serialized result, or what happens on a thrown error / non-serializable value) should have been mentioned to let an agent call this correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 0%, so the description carries the burden and does so usefully: it clarifies that 'script' can be a bare expression ("document.title") or a function body requiring an explicit return. That is real semantic guidance beyond the bare string type.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource: 'Run JavaScript in the page.' This is clearly distinguishable from read-oriented siblings like browser_get_text or browser_snapshot, though it never explicitly names them or notes its overlap with browser_console/chrome_evaluate.

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?

The description explains the two argument forms but gives no guidance on when to reach for this tool versus browser_get_text, browser_snapshot, or browser_console. No prerequisites, no when-not, no alternatives are stated.

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

Deploy Server

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