Playwright MCP

browser_evaluate

Destructive

Run JavaScript expressions on a web page or specific element to extract data, inspect state, or perform custom browser actions.

Instructions

Evaluate JavaScript expression on page or element

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

Input Schema

Name	Required	Description
`target`	No	Exact target element reference from the page snapshot, or a unique element selector
`element`	No	Human-readable element description used to obtain permission to interact with the element
`filename`	No	Filename to save the result to. If not provided, result is returned as text.
`function`	Yes	() => { /* code / } or (element) => { / code */ } when element is provided

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.0.77Oct 19, 2026

TDQS

B3.2/5.0

Behavior3/5

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

Annotations already flag destructiveHint=true and readOnlyHint=false, so the agent knows this can modify state. The description adds minimal context beyond that—it mentions 'on page or element' but doesn't warn about the power of arbitrary JS execution or potential side effects. Since the annotation covers the destructive nature, the description's lack of extra detail keeps it at a baseline 3.

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?

A single, clear sentence with no redundant words. The action is front-loaded and easy to parse. This is appropriately concise for a tool whose parameter details are already in the schema.

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 this tool executes arbitrary JavaScript with destructive potential, the description is too sparse. It doesn't mention that the function can modify the page, that results can be saved to a file (though schema covers it), or that there is a separate unsafe variant (browser_run_code_unsafe) that might be more appropriate for certain tasks. The description lacks the context an agent needs to safely and correctly use this tool, especially when annotations already warn about destructiveness but the description provides no additional guidance.

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 description coverage is 100%, so all four parameters are documented in the schema itself. The description does not add any meaning beyond what the schema provides—it doesn't elaborate on the function syntax, target usage, or filename behavior. With high schema coverage, the baseline is 3, and the description contributes nothing extra.

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 verb 'Evaluate' and the resource 'JavaScript expression on page or element', making the core purpose obvious. However, it doesn't distinguish from the sibling browser_run_code_unsafe, which might also execute code, so it loses a point for not differentiating between similar tools.

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?

There is no guidance on when to use this tool versus alternatives like browser_run_code_unsafe or when to avoid it. No context about prerequisites (e.g., page must be loaded) or scenarios that favor this tool over others. The description simply states the action without any usage direction.

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