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Fast Browser MCP

Fast Browser MCP

by kqlio67
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Local

browser_launch

Launch an isolated Chrome or Chromium instance with CDP remote debugging enabled to automate a real browser, optionally preserving logins through a persistent profile.

Instructions

Launch an isolated Chrome or Chromium browser instance with CDP remote debugging enabled.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "browser_launch"
  }
}

Input Schema

NameRequiredDescriptionDefault
portNoTarget port (picks free port if omitted)
headlessNoWhether to run headless
profile_nameNoOptional name for persistent profile directory (e.g. 'default', 'work'), preserving logins across restarts
user_data_dirNoCustom user profile path

Schema Changelog

Changes observed during successful MCP inspections.

  1. Addedv0.12.0

TDQS

C2.9/5.0
Behavior2/5

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

No annotations are provided, so the description carries the full behavioral burden, yet it only restates the launch + CDP fact. It does not say whether the call must precede other browser_* tools, what handle/session it yields, what happens if an instance is already running, or what 'isolated' implies for state (only the profile_name schema field hints at persistence).

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?

A single front-loaded sentence with no filler or repetition. It is efficient, though the same brevity is what leaves the behavioral and usage gaps unaddressed.

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?

For a lifecycle-anchoring tool in a 70+ sibling browser family, with no annotations and no output schema, the agent needs to know what launching returns (a browser identifier? port for CDP?) and how it relates to subsequent tools. Neither is provided, so the definition is under-specified for its role.

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 port, headless, profile_name, and user_data_dir are already fully documented, including the free-port fallback and login persistence. The description adds no parameter-level meaning beyond that, which is the baseline case for a fully documented schema.

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?

States a specific verb and resource ('Launch an isolated Chrome or Chromium browser instance') plus the distinguishing trait of CDP remote debugging being enabled. It does not distinguish itself from sibling browser_connect or browser_new_isolated_tab, which an agent could confuse it with, so it stops short of a 5.

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 call this versus browser_connect (attach to an existing browser) or when a fresh instance is required, and no mention of prerequisites such as having Chrome/Chromium installed. The agent must infer the place of this tool in the session lifecycle from the sibling list alone.

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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