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Browser Bridge MCP

Browser Bridge MCP

by adbarc92
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Local

browser_evaluate

Run JavaScript code in any browser tab and retrieve the evaluated output.

Instructions

Execute JavaScript in the context of a browser tab and return 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": {
      "expression": "<expression>"
    },
    "name": "browser_evaluate"
  }
}

Input Schema

NameRequiredDescriptionDefault
tabIdNoTab ID (defaults to active tab)
expressionYesJavaScript expression to evaluate

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv1.2.1

TDQS

B3.1/5.0
Behavior2/5

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

There are no annotations provided, and the description does not disclose side effects (e.g., whether the JavaScript execution is read-only or can modify the page), permissions required, or error behavior. This is a significant gap 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.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single sentence that concisely conveys the core functionality. It is front-loaded and contains no filler, though it could benefit from a bit more structure.

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 the absence of an output schema, the description should clarify the return format (e.g., JSON serialization, error behavior). The tool has 11 siblings, yet no contextualization is provided. The description feels incomplete for a JavaScript evaluation tool.

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 schema already provides descriptions for both parameters (tabId and expression) with 100% coverage. The description adds no additional meaning beyond 'execute JavaScript', so a baseline score of 3 is appropriate.

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 JavaScript'), the target ('in the context of a browser tab'), and the outcome ('return the result'). It is specific and distinguishes from siblings like browser_get_content or browser_click.

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?

No guidance is given on when to use this tool versus alternatives such as browser_get_content or browser_click. The description does not mention prerequisites, limitations, or when not to use it.

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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