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Fast Browser MCP

Fast Browser MCP

by kqlio67
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Local

browser_set_user_agent

Set a custom User-Agent string for a browser tab to emulate different devices, browsers, or clients for testing and compatibility.

Instructions

Override User-Agent string for the browser tab.

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": {
      "user_agent": "<user_agent>"
    },
    "name": "browser_set_user_agent"
  }
}

Input Schema

NameRequiredDescriptionDefault
user_agentYesNew User-Agent string

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.8.0

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. It does not state whether the override persists across navigation, applies to existing or only future requests, requires a reload, is reversible, or is scoped per-tab. 'Override' implies mutation but the side effects and lifetime are undisclosed.

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 efficient sentence with the resource and scope front-loaded and no filler. It is appropriately sized, though arguably too terse to earn full marks given the missing behavioral detail.

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

Completeness3/5

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

With 100% schema coverage the parameter is fully specified, so an agent can invoke the tool correctly. However, with no annotations and no output schema, the description leaves the mutation's persistence and reversibility unexplained, which is a meaningful gap for a state-changing 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?

Schema description coverage is 100%, so the single user_agent parameter is already fully documented in the schema. The description adds no format, validity constraints, or examples beyond what the schema provides, so the baseline 3 applies.

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 (Override/set) plus the exact resource (User-Agent string) and scopes it to the browser tab. An agent can understand the operation immediately, though it doesn't explicitly distinguish itself from similar siblings like browser_set_headers or browser_stealth_mode.

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 when-to-use guidance, prerequisites, or alternatives are given. The description doesn't say how this differs from browser_set_headers, browser_emulate_environment, or browser_stealth_mode, which could plausibly also affect the User-Agent.

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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