go-client-langfuse

⚠️ Note: This library is not officially maintained by Langfuse. It’s a community-driven project and is actively being developed.

go-client-langfuse is a Go client library for accessing the Langfuse API.

Table of Contents

• Installation
• Usage
  • Authentication
  • Creating a Client
  • Projects
  • Prompts
• Examples
• Error Handling
• Testing
• Contributing
• License

Installation

go-client-langfuse is compatible with modern Go releases in module mode, with Go installed:

go get github.com/MyCarrier-DevOps/go-client-langfuse@v1.0.0

will resolve and add the package to the current development module, along with its dependencies.

Alternatively the same can be achieved if you use import in a package:

import "github.com/MyCarrier-DevOps/go-client-langfuse/langfuse"

and run go get without parameters.

Usage

import "github.com/MyCarrier-DevOps/go-client-langfuse/langfuse"

Authentication

The Langfuse API uses HTTP Basic Authentication with your public and secret keys. The library handles this automatically using environment variables.

Set the following environment variables:

export LANGFUSE_SERVER_URL="https://cloud.langfuse.com"  # or your self-hosted URL
export LANGFUSE_PUBLIC_KEY="pk-lf-..."
export LANGFUSE_SECRET_KEY="sk-lf-..."

Creating a Client

You can create a client in two ways:

Option 1: Using Environment Variables

Load the configuration from environment variables, then create a client:

package main

import (
    "log"
    "github.com/MyCarrier-DevOps/go-client-langfuse/langfuse"
)

func main() {
    // Load configuration from environment variables
    config, err := langfuse.LoadConfigFromEnvVars()
    if err != nil {
        log.Fatalf("Failed to load config: %v", err)
    }

    // Create a new client with the loaded configuration
    client := langfuse.NewClient(config)

    // Use the client...
}

Option 2: Direct Configuration (Without Environment Variables)

Create a configuration directly without environment variables:

package main

import (
    "log"
    "github.com/MyCarrier-DevOps/go-client-langfuse/langfuse"
)

func main() {
    // Create configuration directly
    config, err := langfuse.NewConfig(
        "https://cloud.langfuse.com",
        "pk-lf-xxx",
        "sk-lf-xxx",
    )
    if err != nil {
        log.Fatalf("Failed to create config: %v", err)
    }

    // Create a new client with the config
    client := langfuse.NewClient(config)

    // Use the client...
}

The client uses retryable HTTP requests with the following default configuration:

• Max Retries: 3 attempts
• Retry Wait Min: 1 second
• Retry Wait Max: 4 seconds
• Retry Policy: Retries on 5xx errors and network failures

Projects

Get information about the project associated with your API keys:

project, err := client.Projects.GetProject()
if err != nil {
    log.Fatalf("Error fetching project: %v", err)
}

fmt.Printf("Project ID: %v\n", project["id"])
fmt.Printf("Project Name: %v\n", project["name"])

Prompts

The library provides comprehensive support for managing prompts in Langfuse.

List All Prompts

prompts, err := client.Prompts.GetPrompts()
if err != nil {
    log.Fatalf("Error fetching prompts: %v", err)
}

fmt.Printf("Prompts: %+v\n", prompts)

Get a Specific Prompt

Retrieve a prompt by name with optional label or version:

// Get latest version with no label
prompt, err := client.Prompts.GetPromptByName("my-prompt", "", nil)
if err != nil {
    log.Fatalf("Error fetching prompt: %v", err)
}

// Get prompt with specific label
prompt, err := client.Prompts.GetPromptByName("my-prompt", "production", nil)

// Get specific version
version := 3
prompt, err := client.Prompts.GetPromptByName("my-prompt", "", &version)

Create a New Prompt

Create a text prompt:

newPrompt := &langfuse.Prompt{
    Name:          "simple-text-prompt",
    Type:          "text",
    Prompt:        "Translate the following text to French: {{text}}",
    Labels:        []string{"production"},
    Tags:          []string{"translation", "french"},
    CommitMessage: "Initial version",
}

createdPrompt, err := client.Prompts.CreatePrompt(newPrompt)
if err != nil {
    log.Fatalf("Error creating prompt: %v", err)
}

Create a chat prompt:

chatPrompt := &langfuse.Prompt{
    Name: "chat-assistant",
    Type: "chat",
    Prompt: []langfuse.ChatMessage{
        {
            Type:    "chatmessage",
            Role:    "system",
            Content: "You are a helpful assistant that answers questions concisely.",
        },
        {
            Type:    "chatmessage",
            Role:    "user",
            Content: "{{user_question}}",
        },
    },
    Labels:        []string{"production", "v1"},
    Tags:          []string{"chat", "assistant"},
    CommitMessage: "Initial chat prompt",
}

createdPrompt, err := client.Prompts.CreatePrompt(chatPrompt)
if err != nil {
    log.Fatalf("Error creating chat prompt: %v", err)
}

Update Prompt Version Labels

Update the labels for a specific prompt version. Note that labels must be unique across all versions of a prompt, and the latest label is reserved and managed by Langfuse:

// Update labels for version 1 of "my-prompt"
updatedPrompt, err := client.Prompts.UpdatePromptVersionLabels(
    "my-prompt",
    1,
    []string{"staging", "beta"},
)
if err != nil {
    log.Fatalf("Error updating prompt version labels: %v", err)
}

fmt.Printf("Updated prompt version %d with labels: %v\n",
    updatedPrompt.Version,
    updatedPrompt.Labels)

Common use cases:

• Promote a version from "staging" to "production"
• Add experiment labels like "beta" or "canary"
• Remove labels by providing a new list that excludes them
• Clear all labels by providing an empty slice []string{}

Examples

For a complete working example, see example/example.go.

To run the example:

# Set environment variables
export LANGFUSE_SERVER_URL="https://cloud.langfuse.com"
export LANGFUSE_PUBLIC_KEY="your-public-key"
export LANGFUSE_SECRET_KEY="your-secret-key"

# Run the example
go run example/example.go

Error Handling

The library uses Go's standard error handling. All API methods return an error as the last return value:

project, err := client.Projects.GetProject()
if err != nil {
    // Handle error
    log.Printf("Error: %v", err)
    return
}

Errors are wrapped with context to help identify where issues occurred:

• error making request: - HTTP request failed (network issues, timeouts)
• client error 4xx: - Client errors (bad request, unauthorized, not found, etc.)
• server error 5xx: - Server errors (internal server error, service unavailable)
• error unmarshalling: - Failed to parse JSON response
• error fetching project: - Project-specific operation failed
• error fetching prompt: - Prompt-specific operation failed

Testing

The library includes comprehensive test coverage. To run tests:

# Run all tests
go test ./langfuse

# Run with verbose output
go test -v ./langfuse

# Run with coverage
go test -cover ./langfuse

# Run specific test
go test -v -run TestClient_Do_Success ./langfuse

Tests use mock HTTP servers to avoid making real API calls.

API Coverage

The library currently supports the following Langfuse API endpoints:

Projects API

• GET /api/public/projects - Get project information

Prompts API

• GET /api/public/v2/prompts - List all prompts
• GET /api/public/v2/prompts/{name} - Get prompt by name (with optional label/version)
• POST /api/public/v2/prompts - Create a new prompt or version
• PATCH /api/public/v2/prompts/{name}/versions/{version} - Update prompt version labels

Roadmap

Future enhancements planned:

• Support for Traces API
• Support for Generations API
• Support for Observations API
• Support for Datasets API
• Support for Scores API
• Context-aware request cancellation
• Additional configuration options
• Pagination helpers

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

When contributing:

1. Fork the repository
2. Create your feature branch (git checkout -b feature/amazing-feature)
3. Write tests for your changes
4. Ensure all tests pass (go test ./...)
5. Run linting (golangci-lint run)
6. Commit your changes (git commit -m 'Add some amazing feature')
7. Push to the branch (git push origin feature/amazing-feature)
8. Open a Pull Request

Versioning

This library follows Semantic Versioning.

Resources

• Langfuse Documentation
• Langfuse API Reference
• Langfuse GitHub

Support

For issues, questions, or contributions, please visit the GitHub repository.