L Harness is a self-hosted, MIT-licensed CRM for LINE Official Accounts, written in TypeScript and deployed on Cloudflare Workers with a D1 database, aimed at teams that want step messaging, broadcasts, forms and reservations without paying a monthly platform fee.

What it is

L Harness is an open-source customer relationship management system for LINE Official Accounts. It lives in the Cloudflare Workers ecosystem, stores data in Cloudflare D1, and is written in TypeScript under the MIT licence. The repository is Shudesu/line-harness-oss, maintained by Shudesu (野田修一) of AIエージェント株式会社, at version v0.21.0 with 591 stars, 383 forks and 50 open issues. Since 2026-08-19 the product display name has been unified as "L Harness", while the repository URL, the create-line-harness command and the @line-harness/* package scope are kept as compatible identifiers so that existing installations are not broken. The project ships an MCP server and a TypeScript SDK alongside the application itself.

The concrete problem it solves is the monthly subscription and closed-source lock-in of commercial LINE marketing automation, which the README refers to as L社 and U社 and prices at from ¥20,000 and from ¥10,000 per month respectively. L Harness replaces those hosted services with software the operator runs inside their own Cloudflare account, covering step messaging, segment broadcasts, rich menu switching, LIFF forms, lead scoring, IF-THEN automation, multi-account operation, BAN detection and duplicate friend detection. Both compared products are closed-source and neither publishes an API, whereas L Harness exposes its full functionality through an API and drives Claude Code through a bundled MCP server.

Key capabilities

• Step messaging controlled at minute granularity through delay_minutes, with conditional branching and stealth sending.
• Broadcasts to all friends, to tags, or to segments, sent immediately or scheduled, with recipients past 500 people placed into an automatic queue.
• Reminder delivery that counts down from a specified date, so a seminar can trigger three days before, one day before and on the day.
• Templates using {{name}}, {{uid}} and {{auth_url:CHANNEL_ID}} for per-recipient personalisation.
• Tracking links that record clicks, then apply automatic tagging and start a scenario.
• Behaviour-based lead scoring, tagging that acts as both a broadcast condition and a scenario trigger, and operator chat.
• BAN detection with automatic account switching, standard multi-account support, and duplicate friend detection by comparing picture_url tokens.
• A bundled MCP server for operation from Claude Code, plus a β plugin market where extensions are scaffolded with pnpm plugin:create ../my-plugin.

Who uses it and how

• Operators running LINE Official Accounts who need step messaging, broadcasts, forms and reservations in a single self-hosted stack rather than several subscriptions.
• Organisations with more than one LINE account: multi-account support is standard instead of a separate contract, and BAN detection switches accounts automatically.
• Marketers who want an external AI to drive campaigns, using the bundled MCP server so Claude Code can operate the CRM through MCP.
• Developers extending the product, who place delivery rules, automation and external integrations into their own repositories and Workers so that core updates do not overwrite custom code.
• Teams that would rather not operate anything themselves, using L Harness Cloud, the managed service built and run by the developer as a separate entity from the open-source project.

Getting started

Setup runs through one command, npx create-line-harness, requiring Node.js 22 or newer, pnpm, a Cloudflare account that works on the free tier, and a LINE Official Account with a Messaging API channel. The CLI performs wrangler login, creates the D1 database and applies schema and migrations, deploys the Worker and admin interface, registers the LINE credentials, creates the LIFF app, and creates the first Owner user, which the README describes as taking about five minutes.

How it compares

The README benchmarks L Harness against two paid products it anonymises as L社, from ¥20,000 per month, and U社, from ¥10,000 per month, both of which keep their source code closed and expose no API. L Harness charges ¥0 for software use, is published under MIT, makes multi-account operation standard rather than a separate contract, and lists scoring, IF-THEN automation, BAN detection and duplicate friend detection as missing from one or both of those products. LINE delivery fees, Cloudflare usage, a custom domain, integration and maintenance work, and any connected external AI service are billed separately from the software.

When to use it — and when not to

A self-hoster must operate a Cloudflare Workers deployment and a D1 database, hold a LINE Official Account with a Messaging API channel, and cover LINE delivery costs, Cloudflare usage, domain and external AI charges separately; the D1 free plan returns query errors once daily read and write limits are reached rather than billing overage, which behaves differently from a paid plan. A team that wants managed hosting, contractual support or someone else to run the infrastructure should choose L Harness Cloud instead of this repository. The plugin market is in β with per-plugin manual setup, plugin source isolation does not guarantee API compatibility, so connections should be verified in a test environment before updating the core or the SDK, and the research and verification material linked from the README is published by the developer rather than being an independent third-party review.

# 本体リポジトリのルートで実行（Node.js 22以上）
pnpm plugin:create ../my-plugin

npx create-line-harness

[ LINE Platform ] ⇄ [ Cloudflare Worker (Hono) ] ⇄ [ D1 SQLite ]
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                    [ Cloudflare Pages (Next.js 15) ]
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                    [ MCP Server / SDK / Claude Code ]