Lemon Editor Extension

A Chrome MV3 extension and local TypeScript service for turning ChatGPT responses into polished, editable PDFs.

Lemon adds an export workflow directly to ChatGPT, opens a full-screen editor for final adjustments, and generates PDFs with configurable typography, pagination, borders, density, and mixed RTL/LTR content.

Engineering highlights

• Chrome Manifest V3 extension with content-script UI injection
• Full-screen editor for editing generated content before export
• Mixed Persian/English RTL and LTR support, including per-line direction controls
• Local Express API for Markdown/HTML-to-PDF rendering
• TypeScript monorepo with shared development scripts
• Configurable page layout, font size, density, borders, page numbers, and pagination
• Build, test, lint, and type-check workflows
• Separation between browser UX and document-rendering service

Technology

TypeScript · Chrome Extension MV3 · Node.js · Express · HTML/CSS · Markdown · PDF generation · npm workspaces

Architecture

ChatGPT page
  │
  ▼
Chrome MV3 extension
  ├── injects Export PDF action
  ├── collects response content
  ├── opens export settings
  └── launches advanced editor
        │
        ▼
Local Express service
  ├── validates Markdown / HTML
  ├── applies layout options
  └── renders final PDF

Main features

• In-page Export PDF action
• Direct export or advanced editing workflow
• Font selection from a bundled Persian font set
• Automatic or manual document direction
• Per-line RTL/LTR controls
• Smart pagination and optional page borders
• Configurable page numbers, density, and font size
• HTML-mode export so the PDF matches edited content

Repository structure

packages/
  extension/   # Chrome MV3 extension
  service/     # Express PDF-generation API
package.json   # workspace scripts
.env.example   # service and extension configuration

Requirements

• Node.js 20+
• npm 10+
• Google Chrome or another Chromium-based browser

Install

npm install
cp .env.example .env

Development

npm run dev

Quality checks:

npm run build
npm run test
npm run lint
npm run typecheck

Load the extension

1. Build the extension:

   npm run build:extension

2. Open chrome://extensions.

3. Enable Developer mode.

4. Choose Load unpacked.

5. Select packages/extension/dist.

6. Open ChatGPT and use the injected export action.

Service API

Health check

GET /health

Generate PDF

POST /api/v1/markdown-to-pdf

Example payload:

{
  "markdown": "# Hello",
  "title": "Example document",
  "filename": "example.pdf",
  "options": {
    "direction": "auto",
    "pageNumbers": true,
    "pageBorder": true,
    "smartPagination": true,
    "fontSize": "medium",
    "density": "normal",
    "codeWrap": false
  }
}

When html is supplied, the service renders the edited HTML directly. Otherwise, markdown is required.

Configuration

The root .env controls both services. Important variables include:

• SERVICE_PORT
• SERVICE_MAX_MARKDOWN_LENGTH
• SERVICE_JSON_BODY_LIMIT
• SERVICE_ALLOWED_ORIGINS
• SERVICE_ALLOW_CHROME_EXTENSION_ORIGINS
• EXTENSION_API_BASE_URL
• EXTENSION_FILENAME_PREFIX

Manual smoke test

1. Start the service with npm run dev:service.
2. Build and reload the extension.
3. Open a ChatGPT response and select Export PDF.
4. Change layout settings and export directly.
5. Repeat with Full Editor.
6. Edit text, font, and direction settings.
7. Confirm the final PDF matches the edited document.

Security and privacy

Lemon is designed around a local rendering service. Before exposing that service beyond localhost:

• restrict allowed origins
• set request size limits
• validate HTML and filenames
• place the API behind authentication
• avoid logging private document content

Project status

Lemon demonstrates browser-extension engineering, TypeScript monorepo organization, full-stack API integration, document rendering, and multilingual UI design.