@meltstudio/langfuse-mcp-server/README.md

MCP server for Langfuse prompt management - get and compile prompts directly in Cursor

# Langfuse MCP Server for Cursor

Get and compile your Langfuse prompts directly in Cursor. No more copying and pasting—just chat with your prompts.

## Quick Start

### 1. Install

```bash
npm install -g @meltstudio/langfuse-mcp-server
```

### 2. Get Your Langfuse Credentials

1. Go to your [Langfuse project settings](https://cloud.langfuse.com)
2. Copy your **Secret Key** and **Public Key**

### 3. Configure Cursor

Add this to your Cursor settings file (`.cursor/mcp.json`):

```json
{
  "mcpServers": {
    "langfuse": {
      "command": "melt-langfuse-mcp",
      "env": {
        "LANGFUSE_SECRET_KEY": "sk-lf-your-secret-key-here",
        "LANGFUSE_PUBLIC_KEY": "pk-lf-your-public-key-here"
      }
    }
  }
}
```

### 4. Restart Cursor

### 5. Test Your Integration

After Cursor restarts, test that everything is working:

1. **Test with direct prompt execution** (Recommended):
   - In Cursor chat, type: **`Use the melt-integration-test prompt`**
   - You should see a welcome message confirming everything works
   - To test with variables: **`Use the melt-integration-test prompt with my_name='YourName' and task='building AI apps'`**

2. **Test with MCP tools**:
   - Ask Cursor: *"Show me all my prompts"*
   - Ask Cursor: *"Get the melt-integration-test prompt"*
   - Ask Cursor: *"Compile melt-integration-test with my_name='YourName' and task='building AI apps'"*

If any of these work, you're all set! 🎉

## Updating

To update to the latest version:

```bash
npm update -g @meltstudio/langfuse-mcp-server
```

Or to force reinstall:

```bash
npm install -g @meltstudio/langfuse-mcp-server@latest
```

After updating, restart Cursor to use the new version.

You can check your installed version with:

```bash
melt-langfuse-mcp --version
```

## Usage

The MCP server provides two ways to work with your Langfuse prompts:

### 1. Direct Prompt Integration (Recommended)
Use Cursor's prompt selector to browse and use your Langfuse prompts directly in chat:

1. Open Cursor's prompt selector (usually `@` in chat)
2. Browse your available Langfuse prompts
3. Select a prompt to use it directly in your conversation
4. Provide variables if the prompt requires them

### 2. Manual Tool Usage
You can also chat naturally with Cursor using these commands:

- **"Show me all my prompts"** - Lists your Langfuse prompts
- **"Get the movie-critic prompt"** - Fetches a specific prompt  
- **"Compile movie-critic with movie='Dune 2'"** - Gets prompt ready for use

## Example

```
You: "Get my movie-critic prompt and compile it for Dune 2"

Cursor: I'll fetch your movie-critic prompt and compile it for Dune 2.

[Gets the prompt from Langfuse and substitutes variables]

Here's your compiled prompt:
"You are an expert movie critic. Write a detailed review of Dune 2..."
```

## Available Commands

| What you want | Say this |
|---------------|----------|
| See all prompts | "List my prompts" or "Show me all prompts" |
| Get a specific prompt | "Get the [prompt-name] prompt" |
| Compile with variables | "Compile [prompt-name] with variable='value'" |
| Get prompt details | "Tell me about the [prompt-name] prompt" |

## Configuration Options

You can add these optional environment variables to your Cursor config:

```json
{
  "mcpServers": {
    "langfuse": {
      "command": "melt-langfuse-mcp",
      "env": {
        "LANGFUSE_SECRET_KEY": "sk-lf-...",
        "LANGFUSE_PUBLIC_KEY": "pk-lf-...",
        "LANGFUSE_HOST": "https://us.cloud.langfuse.com",
        "LANGFUSE_DEFAULT_LABEL": "production"
      }
    }
  }
}
```

## Troubleshooting

### "Command not found" error
Make sure you installed globally: `npm install -g @meltstudio/langfuse-mcp-server`

### "Authentication failed" error  
Double-check your Langfuse credentials in the Cursor config.

### "Prompt not found" error
- Check the prompt name is correct
- Make sure the prompt has the "production" label (or set `LANGFUSE_DEFAULT_LABEL` to match your label)

## Langfuse Regions

**US Region (default):** `https://us.cloud.langfuse.com`  
**EU Region:** `https://cloud.langfuse.com`

The server defaults to US region. For EU region or self-hosted, set your host:

```json
"LANGFUSE_HOST": "https://cloud.langfuse.com"
```

Or for self-hosted:
```json
"LANGFUSE_HOST": "https://your-langfuse-instance.com"
```

---

**Made by [Melt Studio](https://meltstudio.co)** 

Questions? [Open an issue](https://github.com/MeltStudio/melt-langfuse-mcp/issues) or reach out to us.