Line Chrome MCP

Local gateway that turns the LINE Chrome Extension UI into a stable automation surface:

• REST API (/v1)

• Server-Sent Events for gateway events (/v1/events)

• MCP Streamable HTTP (/mcp, including SSE streaming when the protocol uses a stream)

• MCP stdio (line-mcp) implemented as a thin proxy over the local REST gateway

The DOM/CDP adapter is intentionally hidden behind the messaging core. MCP clients and REST callers never depend on LINE CSS class names or DOM implementation details.

Status

This is an initial working prototype built from the observed LINE Extension DOM contract. It supports:

• chat listing/search

• reading text/image/sticker message metadata

• virtualized chat/message scrolling

• incoming message events for the currently rendered active chat

• visible chat-list change events

• queued/idempotent text sending with post-send message-ID verification

• REST + MCP stdio + MCP Streamable HTTP

Not yet implemented: reply sending, file/image upload, reactions, durable storage, and full background message capture for chats that are never rendered by the LINE UI.

Related MCP server: line-desktop-mcp

Requirements

• Node.js 20+

• Chromium/Chrome with the LINE Chrome Extension installed and logged in

• a dedicated Chrome profile launched with DevTools remote debugging enabled

Chrome 136+ does not allow remote debugging against the normal default user-data directory. Use a dedicated profile.

Example:

google-chrome \
  --user-data-dir="$HOME/.line-mcp-profile" \
  --remote-debugging-port=9222

Open LINE in that profile and log in.

Install

npm install
npm run build

Copy .env.example values into your environment as needed. The defaults are:

LINE_CDP_URL=http://127.0.0.1:9222
LINE_EXTENSION_ID=ophjlpahpchlmihnnnihgmmeilfjmjjc
LINE_GATEWAY_HOST=127.0.0.1
LINE_GATEWAY_PORT=8787

LINE_EXTENSION_ID can be omitted; the adapter will then look for a Chrome extension page containing LINE-specific ARIA/DOM markers.

Start the gateway

npm start

Development mode:

npm run dev

Endpoints:

REST API:           http://127.0.0.1:8787/v1
OpenAPI metadata:   http://127.0.0.1:8787/openapi.json
Event SSE:          http://127.0.0.1:8787/v1/events
MCP HTTP:           http://127.0.0.1:8787/mcp

REST API

Health / status

curl http://127.0.0.1:8787/v1/health
curl http://127.0.0.1:8787/v1/status
curl http://127.0.0.1:8787/v1/capabilities

Chats

curl 'http://127.0.0.1:8787/v1/chats?limit=50'
curl 'http://127.0.0.1:8787/v1/chats?q=Pai'
curl 'http://127.0.0.1:8787/v1/chats?unread=true'

Messages

curl 'http://127.0.0.1:8787/v1/chats/CHAT_ID/messages?limit=50'

Older page:

curl 'http://127.0.0.1:8787/v1/chats/CHAT_ID/messages?limit=50&before=MESSAGE_ID'

Send text

curl -X POST 'http://127.0.0.1:8787/v1/chats/CHAT_ID/messages' \
  -H 'Content-Type: application/json' \
  -H 'Idempotency-Key: workflow-run-123' \
  -d '{"text":"ทดสอบส่งจาก API"}'

The request returns 202 Accepted with an operation. Poll it:

curl http://127.0.0.1:8787/v1/operations/OPERATION_ID

UI write operations are serialized so two agents cannot switch LINE chats and type at the same time.

Gateway event SSE

curl -N http://127.0.0.1:8787/v1/events

Current event families include:

message.created
message.sent
chat.updated
operation.created
operation.started
operation.succeeded
operation.failed

message.created is generated for newly rendered messages in the active chat. chat.updated is generated when a visible chat-row preview/unread state changes.

MCP Streamable HTTP

Use:

http://127.0.0.1:8787/mcp

This uses the current MCP Streamable HTTP server entry. Streaming responses use SSE when required by MCP. It is not the deprecated legacy standalone HTTP+SSE transport.

Tools:

line_get_status
line_get_capabilities
line_search_chats
line_get_messages
line_send_message
line_get_operation

MCP stdio

The stdio process does not own Chrome or LINE. It calls the already-running gateway over localhost, so multiple MCP hosts do not create competing LINE sessions.

LINE_GATEWAY_URL=http://127.0.0.1:8787 node dist/mcp/stdio.js

Example MCP host configuration:

{
  "mcpServers": {
    "line": {
      "command": "node",
      "args": ["/absolute/path/to/Line-Chrome-MCP/dist/mcp/stdio.js"],
      "env": {
        "LINE_GATEWAY_URL": "http://127.0.0.1:8787"
      }
    }
  }
}

Authentication / remote binding

By default the service binds to 127.0.0.1 without authentication.

If LINE_GATEWAY_HOST is changed to a non-loopback address, startup is refused unless LINE_GATEWAY_TOKEN is set.

Then use:

Authorization: Bearer <token>

The same token is used by line-mcp via LINE_GATEWAY_TOKEN.

Architecture

LINE Chrome Extension
        │
        │ DOM / CDP
        ▼
ChromeLineAdapter
        │
        ▼
MessagingGateway
  ├─ serialized UI queue
  ├─ operations + idempotency
  └─ event bus
        │
        ├─ REST /v1
        ├─ SSE /v1/events
        └─ MCP /mcp

MCP stdio client
        │ stdin/stdout
        ▼
line-mcp thin proxy
        │ REST localhost
        ▼
MessagingGateway

DOM strategy

The adapter avoids generated CSS module names wherever possible and targets observed semantic markers such as:

button[aria-label="Go chatroom"]
div[data-is-dropzone="true"][data-mid]
[data-message-id]
[data-message-select-id]
[data-timestamp]
[data-is-message-text="true"]
textarea-ex[placeholder="Enter a message"]

LINE uses virtualized lists, so chat enumeration and history reads scroll and deduplicate by stable IDs instead of assuming the entire history exists in document.body at once.

Security note

This project automates an already logged-in personal LINE client. Treat the gateway as sensitive local software. Do not expose it to a network without authentication and additional access controls appropriate to your environment.