• Letter‑by‑letter streaming via WebSocket with a smooth typewriter effect.
• Markdown rendering with KaTeX math and Mermaid diagram support.
• Code blocks with syntax highlighting (highlight.js), copy, and wrap toggle.
• Animated backgrounds with theme‑aware accent glow.
• Multi‑provider ready: OpenAI, OpenRouter, Anthropic, Gemini, Azure, Ollama, Together, Fireworks, Perplexity, Mistral, DeepSeek, Cohere, LiteLLM, vLLM.

Note: Fern requires you to bring your own API keys. A Welcome popup appears on first launch to guide you to Settings.

• Python 3.10+
• Node.js 18+
• Windows/macOS/Linux

1. Create and activate a Python virtual environment

python -m venv .venv
. .venv\Scripts\Activate.ps1   # PowerShell on Windows

2. Install backend deps

pip install -r requirements.txt

3. Build web UI

cd web
npm install
npm run build    # outputs to web/dist

4. Run Electron (spawns FastAPI automatically)

cd ../electron
npm install
npm start

The app will open at http://127.0.0.1:8000 in an Electron window. On first launch, the Welcome modal will prompt you to open Settings and paste your API keys.

Set environment variables before launching (any that apply):

$Env:OPENAI_API_KEY = "sk-..."
$Env:ANTHROPIC_API_KEY = "sk-ant-..."
$Env:GOOGLE_API_KEY = "AIza..."           # Gemini
$Env:OPENROUTER_API_KEY = "sk-or-..."
# ...and so on for the providers you use

You can also paste keys in the Settings dialog in the app.

Fern uses electron-builder for packaging.

1. Ensure the web UI is built:

cd web
npm run build

2. Build installers with electron-builder:

cd ../electron
npm install
npm run dist

Artifacts are written to electron/dist/ (NSIS on Windows, DMG on macOS, AppImage on Linux). Icons are sourced from Assets/Logo.

• Choose themes in Settings; animated background intensity adapts per theme.
• “Glass” UI lets the glow shine through; adjust in web/src/index.css if desired.

• Backend: FastAPI, Uvicorn
• Web: React, Tailwind, marked, highlight.js, katex, mermaid
• Desktop: Electron, electron-builder

PRs welcome! Please open issues for bugs/requests. Ensure web builds and the Electron app starts before submitting changes.

MIT