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umbra

umbra

by lxchx
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Remote

Handoff Start

handoff_start

Starts a live remote-view URL to let a human handle captcha or 2FA steps, paired with a wait call to announce the URL before blocking.

Instructions

Spin up live remote-view URL (192-bit auth token in path). For captcha/2FA/manual steps. tunnel=True (default) → public via cloudflared Quick Tunnel; falls back to 127.0.0.1. Use start/wait PAIR to announce URL before blocking. fps 3 default (8-12 local).

Ex: handoff_start('t0', 'solve recaptcha') → {"url":"https://abc.trycloudflare.com/h-XYZ/","reason":"...","next":"tell user to open URL, then call handoff_wait"}

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": {
      "tab_id": "<tab_id>"
    },
    "name": "handoff_start"
  }
}

Input Schema

NameRequiredDescriptionDefault
fpsNo
reasonNouser input needed
tab_idYes
tunnelNo

Output Schema

NameRequiredDescriptionDefault

No arguments

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A4.1/5.0
Behavior4/5

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

With no annotations provided, the description carries the full disclosure burden and does a good job: it explains public exposure via cloudflared Quick Tunnel, fallback to 127.0.0.1, inclusion of a 192-bit auth token in the URL, and the blocking relationship with handoff_wait. It stops short of describing lifecycle cleanup or broader security implications of exposing a live browser session publicly.

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 compact, front-loaded, and uses a concrete example to convey return guidance and next steps. It is dense and telegraphic in places, but nearly every sentence adds operational value.

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 that an output schema exists, the description does not need to explain return values in detail, and the example still helpfully shows the practical result shape. It is complete enough for an agent to start a handoff correctly, with only minor gaps around lifecycle cleanup and explicit tab_id semantics.

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 0%, so the description must compensate for all four parameters. It gives useful meaning for tunnel, fps, and reason, but tab_id is only shown indirectly in the example ('t0') rather than explicitly described, leaving one required parameter under-documented.

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 gives a specific verb and resource: it 'spins up' a live remote-view URL, explicitly for captcha/2FA/manual-step scenarios. It also distinguishes the tool from handoff_wait by explaining the start/wait pairing, so an agent can identify the tool's role without opening the schema.

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?

It clearly states when to use the tool: captcha, 2FA, and manual intervention. It also gives the important sequencing guidance to use start/wait as a pair so the URL is announced before blocking, though it does not explicitly compare against other user-input tools such as request_user_input.

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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