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PhantomHand

PhantomHand

by SilenceEchoLab
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
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browser_eval_js

Execute JavaScript code directly within the active web page's context to retrieve data or trigger actions.

Instructions

Evaluate arbitrary JavaScript in the context of the active page.

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": {
      "code": "<code>"
    },
    "name": "browser_eval_js"
  }
}

Input Schema

NameRequiredDescriptionDefault
codeYes

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv1.0.1

TDQS

B3.3/5.0
Behavior2/5

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

No annotations are provided, so the description carries the full burden. It states 'Evaluate arbitrary JavaScript' but does not disclose key behavioral traits such as side effects on the page, return value format, sandboxing, or error handling. This is insufficient for a tool that executes arbitrary code.

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 that immediately communicates the core purpose. Every word earns its place without unnecessary elaboration.

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

Completeness2/5

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

Given that there is no output schema and only one parameter with no description coverage, the description is too minimal. It omits important details like return values, execution limitations, and potential risks, making it incomplete for a powerful tool.

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

Parameters2/5

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

The description does not add any meaning to the 'code' parameter beyond what the input schema provides (a string). With 0% schema description coverage, the description should compensate but fails to explain what kind of code is valid, context, or return behavior.

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 verb 'Evaluate' and the resource 'arbitrary JavaScript in the context of the active page.' It effectively distinguishes this tool from sibling browser tools that perform specific actions like clicking, typing, or navigating.

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 that this tool is for executing custom JavaScript, but it provides no explicit guidance on when to use it versus alternatives, such as for advanced automation or debugging. No exclusions or prerequisites are mentioned.

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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