veilbrowser

veil_fedcm_enable

Enables FedCM (Federated Credential Management) interception before visiting a site that shows a Google or federated one-tap sign-in on load.

Instructions

Arm FedCM interception BEFORE navigating to a site that shows a Google/federated 'one-tap' sign-in on load. Order: veil_fedcm_enable -> veil_goto the sign-in page -> veil_fedcm_signin. (Skip this for an active 'Sign in with Google' button; veil_fedcm_signin arms itself when you pass a triggerRef.)

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": "veil_fedcm_enable"
  }
}

Input Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.5.0Jul 29, 2026

TDQS

A4.3/5.0

Behavior3/5

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

No annotations are provided, so the description must fully disclose behavior. It states that it 'arms' FedCM interception, which implies setting up some state, but does not explain what exactly happens (e.g., whether it modifies global settings, whether it is reversible, or what the side effects are). For a tool with no parameters, the description is adequate but lacks deeper behavioral detail.

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 concise with two sentences, but the first sentence is somewhat long. It front-loads the purpose and provides additional context in the second sentence. Every sentence adds value, though it could be slightly more streamlined.

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 has no parameters and no output schema, the description covers the essential context: what the tool does, when to use it (before certain sites), and how it relates to sibling tools. It explains the sequence and exceptions. It is complete enough for its simplicity, though it does not mention return values (acceptable since no output schema exists and the action likely returns nothing).

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The tool has zero parameters, and the schema coverage is 100%. Per the rubric, 0 parameters earns a baseline score of 4. The description does not need to add parameter details since there are none. It appropriately focuses on the tool's action and usage.

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 purpose: 'Arm FedCM interception BEFORE navigating to a site that shows a Google/federated 'one-tap' sign-in on load.' It uses a specific verb ('arm') and resource ('FedCM interception'), and distinguishes from the sibling tool 'veil_fedcm_signin' by specifying the different use case (active button vs. automatic sign-in).

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

Usage Guidelines5/5

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

The description explicitly provides a recommended order: 'veil_fedcm_enable -> veil_goto the sign-in page -> veil_fedcm_signin'. It also tells when to skip this tool: 'Skip this for an active 'Sign in with Google' button; veil_fedcm_signin arms itself when you pass a triggerRef.' This gives clear contextual guidance.

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