Skip to main content
Glama
seleniumbase

seleniumbase-mcp

Official
by seleniumbase
OverviewSchemaRelated ServersScoreDiscussions
Python
Local

run_javascript

Execute arbitrary JavaScript in the current page to handle interactions that higher-level browser tools do not expose. Use this when standard clicks or storage operations cannot achieve the required outcome.

Instructions

Evaluate a JavaScript expression in the current page context.

Use this only when the required browser operation cannot be accomplished through the higher-level SeleniumBase tools.

The expression is evaluated through Chrome DevTools Protocol Runtime.evaluate in the currently active page. It executes with access to the page's JavaScript context, including DOM APIs, browser storage, and other same-origin page resources available to JavaScript.

Tool selection: - Prefer click, type_text, select_option, hover_with_action, focus_on, scroll, and other higher-level tools for normal browser interactions. - Prefer get_content, get_attributes, and find_elements for reading page content or element information. - Prefer manage_storage for ordinary localStorage/sessionStorage reads and writes. - Prefer manage_cookies for browser cookie operations. - Use this tool when a required operation needs arbitrary JavaScript that the higher-level tools do not expose.

Args: expression: A JavaScript expression or executable JavaScript code evaluated in the current page. It may reference standard browser globals such as document and window and may use DOM APIs.

    Examples:
        - "document.title"
        - "document.querySelector('button')?.textContent"
        - "localStorage.getItem('theme')"
        - "document.body.classList.contains('dark')"
        - "document.querySelector('#slider').value = '50'"

    The expression should produce a value when a result is needed.
    JavaScript that returns a Promise is supported and its resolved
    value is returned.

Returns: The JavaScript evaluation result when it can be serialized and returned across the MCP boundary. Primitive values, arrays, plain objects, and null are generally suitable return values. DOM objects, functions, symbols, and other non-serializable JavaScript values may not be returned directly; extract the needed property or convert the value to a serializable form first.

Security: This provides unrestricted JavaScript execution in the current browser page. It can read or modify page data and interact with the page in ways that bypass the higher-level tool abstractions. Only expose this MCP server to trusted clients.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
expressionYes

Schema Changelog

Changes observed during successful MCP inspections. Dates show when Glama detected each change.

  1. Addedv1.2.0

TDQS

A5/5.0
Behavior5/5

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

With no annotations provided, the description carries the full burden, and it excels. It discloses execution via Chrome DevTools Protocol Runtime.evaluate in the active page, access to page JS context, Promise support, serialization limits for return values, and a security warning about unrestricted read/write access to page data. Nothing about the tool's behavior is hidden.

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 long but every section earns its place due to the tool's complexity and safety implications. It is well-structured with clear headings (Tool selection, Args, Returns, Security), bulleted lists, and front-loaded purpose. No filler or repetition; the detail is necessary for correct and safe invocation.

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

Completeness5/5

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

Given no output schema and one opaque parameter, the description covers everything an agent needs: what it does, when to use it, what the parameter accepts, what values can be returned, serialization caveats, and security context. Even the return behavior is explained despite no output schema, making the tool fully self-contained.

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

Parameters5/5

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

The input schema has 0% coverage, so the description fully compensates. The Args section defines 'expression' comprehensively: what it is, how it is evaluated, browser globals available, five concrete examples, and guidance on producing values and Promise handling. This goes far beyond the schema's bare parameter name.

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 opens with a precise verb+resource: 'Evaluate a JavaScript expression in the current page context.' It clearly distinguishes itself from sibling tools by stating it is for operations that cannot be accomplished through higher-level SeleniumBase tools, so an agent immediately knows what this tool uniquely does.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage guidance is explicit and actionable. It says 'Use this only when the required browser operation cannot be accomplished through the higher-level SeleniumBase tools' and then lists specific alternative tools to prefer for interactions, reading content, storage, and cookies. It closes with a positive condition: use when arbitrary JavaScript is needed that higher-level tools do not expose.

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

Install Server

Other Tools

Latest Blog Posts

MCP directory API

We provide all the information about MCP servers via our MCP API.

curl -X GET 'https://glama.ai/api/mcp/v1/servers/seleniumbase/seleniumbase-mcp'

If you have feedback or need assistance with the MCP directory API, please join our Discord server