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browser_open

Opens a URL in a cloaked Chromium browser to start an interactive browsing session, enabling controlled web navigation for security assessments.

Instructions

Purpose: Open a URL in cloakbrowser Chromium and start an interactive browsing session.… Constraints: url is scope-validated and redirects are revalidated. fingerprint is compatibility-only and non-empty values are rejected. Proxy precedence is parameter, BROWSER_PROXY_URL, then direct… Example: browser_open(url='https://app.target.test/login', session='recon', timezone='America/New_York'…

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": {
      "url": "<url>"
    },
    "name": "browser_open"
  }
}

Input Schema

Name	Required	Default
`url`	Yes
`proxy`	No
`locale`	No
`session`	No	default
`timezone`	No
`fingerprint`	No

Output Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Aug 8, 2026

TDQS

A4.4/5.0

Behavior5/5

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

With no annotations, the description fully discloses key behavioral constraints: URL scope validation, redirect revalidation, fingerprint compatibility-only with rejection of non-empty values, and proxy precedence order. This goes well beyond what the schema or annotations provide.

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 well-structured with Purpose, Constraints, and Example sections. It is front-loaded with the core purpose and every sentence adds value without unnecessary fluff.

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?

Given the tool's complexity (6 params, no annotations), the description covers purpose, constraints, and a usage example. The presence of an output schema covers return-value expectations, though alternative-tool guidance is minimal.

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 description adds meaning for url, proxy, and fingerprint via constraints, and the example shows session and timezone usage. However, locale remains unexplained, and schema descriptions are absent, leaving significant gaps for a 6-parameter tool.

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 states a specific action: 'Open a URL in cloakbrowser Chromium and start an interactive browsing session.' It clearly distinguishes this tool from sibling browser tools (e.g., browser_act, browser_snapshot) by focusing on the initial open and session start.

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

Usage Guidelines4/5

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

The description implies when to use it ('start an interactive browsing session') and provides an example. However, it doesn't explicitly mention alternatives or exclusion criteria, relying on sibling context.

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