line-desktop-mcp

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Log in to LINE

login

Idempotent

Authenticates LINE Desktop by scanning a QR code in a local window; reuses a saved session on each start, or opens the QR and waits for scan/PIN.

Instructions

Call this first. It returns at once when the saved session still works, so it is safe to call on every start. Otherwise it opens the 'Line Desktop MCP' window, shows the QR, and waits up to timeout_sec for the scan plus any PIN LINE asks for. Closing that window stops the wait, in which case nothing is saved.

The window appears on this machine, so the login cannot be completed from a different host. Keep the session file private: it holds the access token and the Letter Sealing keys.

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": "login"
  }
}

Input Schema

Name	Required	Description	Default
`force`	No	Ignore the stored session and always show a fresh QR. A successful login replaces the saved session.
`timeout_sec`	No	How long to wait for the QR scan (and any PIN entry).

Output Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

Addedv4.0.0Nov 6, 2026

TDQS

A4.9/5.0

Behavior5/5

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

Goes well beyond the annotations: it discloses that a window opens, that the wait covers the scan plus any PIN, that closing the window aborts and saves nothing, that login cannot be completed from another host, and that the session file holds the access token and Letter Sealing keys. These are exactly the operational and security facts an agent needs.

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?

Front-loaded with the action and the 'call this first' directive, then the fallback behavior, then the constraints. No sentence is filler.

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

Completeness5/5

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

An output schema exists so return values need not be explained, and the description covers the remaining gaps: timing, abort semantics, host locality, and session-file sensitivity.

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?

Schema coverage is 100%, so the baseline is 3, but the description adds real meaning: timeout_sec covers the scan plus any PIN prompt, and force is tied to the 'successful login replaces the saved session' consequence.

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?

States a specific verb and resource ('Log in by scanning a QR code') plus the mechanism (a window on this machine), which cleanly separates it from the logout sibling.

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?

Explicitly says 'Call this first' and that it is safe to call on every start because it returns at once when the saved session works; the force parameter is framed as the alternative path for a fresh QR.

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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