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execute_javascript

Execute JavaScript in the active browser tab to extract web page data, returning results directly. Faster and more accurate than screenshot OCR.

Instructions

Run JavaScript in the active browser tab. Much faster than screenshot+OCR for web pages. Returns the result.

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": "execute_javascript"
  }
}

Input Schema

Name	Required	Description	Default
`code`	Yes	JavaScript code to execute
`browser`	No	'safari' or 'chrome' (defaults to Safari)

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.0.13May 29, 2026

TDQS

B3.2/5.0

Behavior2/5

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

With no annotations provided, the description must disclose behavioral traits. It confirms execution in the active tab and return of results, but omits critical details: whether code runs in page context, potential side effects (e.g., altering page state), error handling, and security implications. This leaves significant gaps for safe agent invocation.

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 two sentences, front-loading the action and key benefit. Every phrase adds value: 'Run JavaScript', 'Much faster than screenshot+OCR', 'Returns the result'. No wasted words, ideal for quick agent parsing.

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?

Despite no output schema, the description merely says 'Returns the result' without specifying type (string, JSON, etc.) or error behavior. It lacks guidance on what constitutes a valid result or how failures are reported. Given the tool's power (executing arbitrary JS), completeness is inadequate.

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 input schema has 100% coverage: both 'code' and 'browser' are described. The description adds no extra meaning beyond the schema—it repeats the function but doesn't clarify return value format or browser parameter defaults. Baseline 3 is appropriate.

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?

The description clearly states the tool runs JavaScript in the active browser tab and returns the result. It distinguishes itself from screenshot+OCR by noting speed, but doesn't directly compare to sibling tools like click_at or get_page_text. Still, the purpose is specific and actionable.

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 advises using this tool over screenshot+OCR for web page data extraction, implying a performance advantage. However, it does not provide explicit when-to-use or when-not-to-use compared to other siblings like get_page_elements or find_text_on_screen, leaving some ambiguity.

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