Skip to main content
Glama
Sign In
playwright-mcp-server

playwright-mcp-server

by doucej
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Local

evaluate

Execute a JavaScript expression in the current page context and return the serializable result as JSON for extracting data or testing logic.

Instructions

Execute a JavaScript expression in the page context and return the result as JSON. The expression may return any serialisable value.

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": "evaluate"
  }
}

Input Schema

NameRequiredDescriptionDefault
scriptYesJavaScript expression or statement block to evaluate. Wrap multi-statement code in an IIFE if a return value is needed.

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv1.0.0

TDQS

A3.8/5.0
Behavior3/5

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

With no annotations, the description carries the transparency burden. It adds useful context (page context, JSON serializability) but does not disclose error handling, potential side effects of executing arbitrary code, or whether the script runs in an isolated world.

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, direct sentence that conveys all essential information without filler. The key facts are front-loaded.

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

Completeness4/5

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

For a simple, single-parameter tool, the description covers the main purpose and output format. It lacks error behavior and side-effect warnings, but these are not explicitly required for completeness given the tool's simplicity.

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 coverage is 100% and the script parameter is well-documented with IIFE guidance. The description adds that returns are JSON-serializable but does not introduce new parameter semantics beyond the schema.

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 action 'Execute', the target 'a JavaScript expression', the context 'in the page context', and the outcome 'return the result as JSON'. This distinctly separates it from sibling tools that handle navigation, interaction, or extraction.

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?

No explicit guidance is given on when to prefer this tool over siblings. The usage is implied from the nature of the tool (running custom JS), but there are no stated exclusions or alternatives.

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

Deploy Server

Other Tools