Class: Langfuse::Client

Inherits:
Object
  • Object
show all
Defined in:
lib/langfuse/client.rb

Overview

Main client for Langfuse SDK

Provides a unified interface for interacting with the Langfuse API. Handles prompt fetching and returns the appropriate prompt client (TextPromptClient or ChatPromptClient) based on the prompt type.

rubocop:disable Metrics/ClassLength

Examples:

config = Langfuse::Config.new(
  public_key: "pk_...",
  secret_key: "sk_...",
  cache_ttl: 120
)
client = Langfuse::Client.new(config)
prompt = client.get_prompt("greeting")
compiled = prompt.compile(name: "Alice")

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(config) ⇒ Client

Initialize a new Langfuse client

Parameters:

  • config (Config) —

    Configuration object



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# File 'lib/langfuse/client.rb', line 27

def initialize(config)
  @config = config
  @config.validate!

  # Create cache if enabled
  cache = create_cache if cache_enabled?

  # Create API client with cache
  @api_client = ApiClient.new(
    public_key: config.public_key,
    secret_key: config.secret_key,
    base_url: config.base_url,
    timeout: config.timeout,
    logger: config.logger,
    cache: cache
  )

  # Initialize score client for batching score events
  @score_client = ScoreClient.new(api_client: @api_client, config: config)
end

Instance Attribute Details

#api_client ⇒ Object (readonly)

Returns the value of attribute api_client.



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# File 'lib/langfuse/client.rb', line 22

def api_client
  @api_client
end

#config ⇒ Object (readonly)

Returns the value of attribute config.



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# File 'lib/langfuse/client.rb', line 22

def config
  @config
end

Instance Method Details

#compile_prompt(name, variables: {}, version: nil, label: nil, fallback: nil, type: nil) ⇒ String, Array<Hash>

Convenience method: fetch and compile a prompt in one call

This is a shorthand for calling get_prompt followed by compile. Returns the compiled prompt ready to use with your LLM.

Examples:

Compile a text prompt

text = client.compile_prompt("greeting", variables: { name: "Alice" })
# => "Hello Alice!"

Compile a chat prompt

messages = client.compile_prompt("support-bot", variables: { company: "Acme" })
# => [{ role: :system, content: "You are a support agent for Acme" }]

With fallback

text = client.compile_prompt(
  "greeting",
  variables: { name: "Alice" },
  fallback: "Hello {{name}}!",
  type: :text
)

Parameters:

  • name (String) —

    The name of the prompt

  • variables (Hash) (defaults to: {}) —

    Variables to substitute in the prompt

  • version (Integer, nil) (defaults to: nil) —

    Optional specific version number

  • label (String, nil) (defaults to: nil) —

    Optional label (e.g., “production”, “latest”)

  • fallback (String, Array, nil) (defaults to: nil) —

    Optional fallback prompt to use on error

  • type (Symbol, nil) (defaults to: nil) —

    Required when fallback is provided (:text or :chat)

Returns:

  • (String, Array<Hash>) —

    Compiled prompt (String for text, Array for chat)

Raises:

  • (ArgumentError) —

    if both version and label are provided

  • (ArgumentError) —

    if fallback is provided without type

  • (NotFoundError) —

    if the prompt is not found and no fallback provided

  • (UnauthorizedError) —

    if authentication fails and no fallback provided

  • (ApiError) —

    for other API errors and no fallback provided



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# File 'lib/langfuse/client.rb', line 138

def compile_prompt(name, variables: {}, version: nil, label: nil, fallback: nil, type: nil)
  prompt = get_prompt(name, version: version, label: label, fallback: fallback, type: type)
  prompt.compile(**variables)
end

#create_prompt(name:, prompt:, type:, config: {}, labels: [], tags: [], commit_message: nil) ⇒ TextPromptClient, ChatPromptClient

Create a new prompt (or new version if name already exists)

Creates a new prompt in Langfuse. If a prompt with the same name already exists, this creates a new version of that prompt.

rubocop:disable Metrics/ParameterLists

Examples:

Create a text prompt

prompt = client.create_prompt(
  name: "greeting",
  prompt: "Hello {{name}}!",
  type: :text,
  labels: ["production"],
  config: { model: "gpt-4o", temperature: 0.7 }
)

Create a chat prompt

prompt = client.create_prompt(
  name: "support-bot",
  prompt: [
    { role: "system", content: "You are a {{role}} assistant" },
    { role: "user", content: "{{question}}" }
  ],
  type: :chat,
  labels: ["staging"]
)

Parameters:

  • name (String) —

    The prompt name (required)

  • prompt (String, Array<Hash>) —

    The prompt content (required)

    • For text prompts: a string with {variable} placeholders

    • For chat prompts: array of message hashes with role and content

  • type (Symbol) —

    Prompt type (:text or :chat) (required)

  • config (Hash) (defaults to: {}) —

    Optional configuration (model parameters, tools, etc.)

  • labels (Array<String>) (defaults to: []) —

    Optional labels (e.g., [“production”])

  • tags (Array<String>) (defaults to: []) —

    Optional tags for categorization

  • commit_message (String, nil) (defaults to: nil) —

    Optional commit message

Returns:

Raises:

  • (ArgumentError) —

    if required parameters are missing or invalid

  • (UnauthorizedError) —

    if authentication fails

  • (ApiError) —

    for other API errors



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# File 'lib/langfuse/client.rb', line 182

def create_prompt(name:, prompt:, type:, config: {}, labels: [], tags: [], commit_message: nil)
  validate_prompt_type!(type)
  validate_prompt_content!(prompt, type)

  prompt_data = api_client.create_prompt(
    name: name,
    prompt: normalize_prompt_content(prompt, type),
    type: type.to_s,
    config: config,
    labels: labels,
    tags: tags,
    commit_message: commit_message
  )

  build_prompt_client(prompt_data)
end

#create_score(name:, value:, trace_id: nil, observation_id: nil, comment: nil, metadata: nil, data_type: :numeric) ⇒ void

This method returns an undefined value.

Create a score event and queue it for batching

rubocop:disable Metrics/ParameterLists

Examples:

Numeric score

client.create_score(name: "quality", value: 0.85, trace_id: "abc123")

Boolean score

client.create_score(name: "passed", value: true, trace_id: "abc123", data_type: :boolean)

Categorical score

client.create_score(name: "category", value: "high", trace_id: "abc123", data_type: :categorical)

Parameters:

  • name (String) —

    Score name (required)

  • value (Numeric, Integer, String) —

    Score value (type depends on data_type)

  • trace_id (String, nil) (defaults to: nil) —

    Trace ID to associate with the score

  • observation_id (String, nil) (defaults to: nil) —

    Observation ID to associate with the score

  • comment (String, nil) (defaults to: nil) —

    Optional comment

  • metadata (Hash, nil) (defaults to: nil) —

    Optional metadata hash

  • data_type (Symbol) (defaults to: :numeric) —

    Data type (:numeric, :boolean, :categorical)

Raises:

  • (ArgumentError) —

    if validation fails



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# File 'lib/langfuse/client.rb', line 263

def create_score(name:, value:, trace_id: nil, observation_id: nil, comment: nil, metadata: nil,
                 data_type: :numeric)
  @score_client.create(
    name: name,
    value: value,
    trace_id: trace_id,
    observation_id: observation_id,
    comment: comment,
    metadata: metadata,
    data_type: data_type
  )
end

#flush_scores ⇒ void

This method returns an undefined value.

Force flush all queued score events

Sends all queued score events to the API immediately.

Examples:

client.flush_scores


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# File 'lib/langfuse/client.rb', line 337

def flush_scores
  @score_client.flush
end

#get_prompt(name, version: nil, label: nil, fallback: nil, type: nil) ⇒ TextPromptClient, ChatPromptClient

Fetch a prompt and return the appropriate client

Fetches the prompt from the Langfuse API and returns either a TextPromptClient or ChatPromptClient based on the prompt type.

Examples:

With fallback for graceful degradation

prompt = client.get_prompt("greeting", fallback: "Hello {{name}}!", type: :text)

Parameters:

  • name (String) —

    The name of the prompt

  • version (Integer, nil) (defaults to: nil) —

    Optional specific version number

  • label (String, nil) (defaults to: nil) —

    Optional label (e.g., “production”, “latest”)

  • fallback (String, Array, nil) (defaults to: nil) —

    Optional fallback prompt to use on error

  • type (Symbol, nil) (defaults to: nil) —

    Required when fallback is provided (:text or :chat)

Returns:

Raises:

  • (ArgumentError) —

    if both version and label are provided

  • (ArgumentError) —

    if fallback is provided without type

  • (NotFoundError) —

    if the prompt is not found and no fallback provided

  • (UnauthorizedError) —

    if authentication fails and no fallback provided

  • (ApiError) —

    for other API errors and no fallback provided



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# File 'lib/langfuse/client.rb', line 67

def get_prompt(name, version: nil, label: nil, fallback: nil, type: nil)
  # Validate fallback usage
  if fallback && !type
    raise ArgumentError, "type parameter is required when fallback is provided (use :text or :chat)"
  end

  # Try to fetch from API
  prompt_data = api_client.get_prompt(name, version: version, label: label)
  build_prompt_client(prompt_data)
rescue ApiError, NotFoundError, UnauthorizedError => e
  # If no fallback, re-raise the error
  raise e unless fallback

  # Log warning and return fallback
  config.logger.warn("Langfuse API error for prompt '#{name}': #{e.message}. Using fallback.")
  build_fallback_prompt_client(name, fallback, type)
end

#list_prompts(page: nil, limit: nil) ⇒ Array<Hash>

List all prompts in the Langfuse project

Fetches a list of all prompt names available in your project. Returns metadata only, not full prompt content.

Examples:

prompts = client.list_prompts
prompts.each do |prompt|
  puts "#{prompt['name']} (v#{prompt['version']})"
end

Parameters:

  • page (Integer, nil) (defaults to: nil) —

    Optional page number for pagination

  • limit (Integer, nil) (defaults to: nil) —

    Optional limit per page

Returns:

  • (Array<Hash>) —

    Array of prompt metadata hashes

Raises:



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# File 'lib/langfuse/client.rb', line 101

def list_prompts(page: nil, limit: nil)
  api_client.list_prompts(page: page, limit: limit)
end

#score_active_observation(name:, value:, comment: nil, metadata: nil, data_type: :numeric) ⇒ void

This method returns an undefined value.

Create a score for the currently active observation (from OTel span)

Extracts observation_id and trace_id from the active OpenTelemetry span.

Examples:

Langfuse.observe("operation") do |obs|
  client.score_active_observation(name: "accuracy", value: 0.92)
end

Parameters:

  • name (String) —

    Score name (required)

  • value (Numeric, Integer, String) —

    Score value

  • comment (String, nil) (defaults to: nil) —

    Optional comment

  • metadata (Hash, nil) (defaults to: nil) —

    Optional metadata hash

  • data_type (Symbol) (defaults to: :numeric) —

    Data type (:numeric, :boolean, :categorical)

Raises:

  • (ArgumentError) —

    if no active span or validation fails



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# File 'lib/langfuse/client.rb', line 293

def score_active_observation(name:, value:, comment: nil, metadata: nil, data_type: :numeric)
  @score_client.score_active_observation(
    name: name,
    value: value,
    comment: comment,
    metadata: metadata,
    data_type: data_type
  )
end

#score_active_trace(name:, value:, comment: nil, metadata: nil, data_type: :numeric) ⇒ void

This method returns an undefined value.

Create a score for the currently active trace (from OTel span)

Extracts trace_id from the active OpenTelemetry span.

Examples:

Langfuse.observe("operation") do |obs|
  client.score_active_trace(name: "overall_quality", value: 5)
end

Parameters:

  • name (String) —

    Score name (required)

  • value (Numeric, Integer, String) —

    Score value

  • comment (String, nil) (defaults to: nil) —

    Optional comment

  • metadata (Hash, nil) (defaults to: nil) —

    Optional metadata hash

  • data_type (Symbol) (defaults to: :numeric) —

    Data type (:numeric, :boolean, :categorical)

Raises:

  • (ArgumentError) —

    if no active span or validation fails



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# File 'lib/langfuse/client.rb', line 319

def score_active_trace(name:, value:, comment: nil, metadata: nil, data_type: :numeric)
  @score_client.score_active_trace(
    name: name,
    value: value,
    comment: comment,
    metadata: metadata,
    data_type: data_type
  )
end

#shutdown ⇒ void

This method returns an undefined value.

Shutdown the client and flush any pending scores

Also shuts down the cache if it supports shutdown (e.g., SWR thread pool).



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# File 'lib/langfuse/client.rb', line 346

def shutdown
  @score_client.shutdown
  @api_client.shutdown
end

#trace_url(trace_id) ⇒ String

Generate URL for viewing a trace in Langfuse UI

Examples:

url = client.trace_url("abc123...")
puts "View trace at: #{url}"

Parameters:

  • trace_id (String) —

    The trace ID (hex-encoded, 32 characters)

Returns:

  • (String) —

    URL to view the trace



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# File 'lib/langfuse/client.rb', line 238

def trace_url(trace_id)
  "#{config.base_url}/traces/#{trace_id}"
end

#update_prompt(name:, version:, labels:) ⇒ TextPromptClient, ChatPromptClient

Update an existing prompt version’s metadata

Updates the labels of an existing prompt version. Note: The prompt content itself cannot be changed after creation.

Examples:

Update labels to promote to production

prompt = client.update_prompt(
  name: "greeting",
  version: 2,
  labels: ["production"]
)

Parameters:

  • name (String) —

    The prompt name (required)

  • version (Integer) —

    The version number to update (required)

  • labels (Array<String>) —

    New labels (replaces existing). Required.

Returns:

Raises:



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# File 'lib/langfuse/client.rb', line 220

def update_prompt(name:, version:, labels:)
  prompt_data = api_client.update_prompt(
    name: name,
    version: version,
    labels: labels
  )

  build_prompt_client(prompt_data)
end