veilbrowser

veil_set_user_agent

Override the User-Agent at runtime, aligning Sec-CH-UA client-hint brands to avoid fingerprint mismatches.

Instructions

Override the User-Agent at runtime, keeping the Sec-CH-UA client-hint brands aligned with it (a bare UA with mismatched hints is a fingerprint tell).

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": {
      "userAgent": "<userAgent>"
    },
    "name": "veil_set_user_agent"
  }
}

Input Schema

Name	Required	Description	Default
`userAgent`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.5.0Jul 29, 2026

TDQS

A3.8/5.0

Behavior4/5

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

Despite lacking annotations, the description adds meaningful behavioral context: it explains that the tool keeps Sec-CH-UA client hints aligned with the new UA to avoid fingerprinting. This goes beyond a simple 'set' action.

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 sentence that is front-loaded with the core action and then adds a crucial behavioral note. No wasted words.

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 setter with one parameter and no output schema, the description is reasonably complete. It explains the purpose and an important side effect. Minor gaps: no error conditions or restrictions mentioned.

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 only parameter, userAgent, is self-explanatory from its name and type, but the description does not specify the expected format or provide examples. With 0% schema coverage, the description compensates partially by explaining the purpose but not the syntax.

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 tool overrides the User-Agent at runtime, which is a specific verb and resource. It distinguishes itself from all sibling tools, none of which deal with user-agent settings.

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 usage guidelines are provided. The description does not indicate when to use this tool versus alternatives, nor does it specify a context or exclusions.

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