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")

Constant Summary collapse

DATASET_ITEMS_PAGE_SIZE =

Returns Default page size when fetching all dataset items.

Returns:

  • (Integer) —

    Default page size when fetching all dataset items

50

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 35

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
  )

  @project_id = nil
  # One-shot lookup: avoids repeated blocking API calls in URL helpers
  # (trace_url, dataset_url, dataset_run_url) when the project endpoint is down.
  @project_id_fetched = false

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

Instance Attribute Details

#api_client ⇒ ApiClient (readonly)

Returns The underlying API client.

Returns:



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# File 'lib/langfuse/client.rb', line 29

def api_client
  @api_client
end

#config ⇒ Config (readonly)

Returns The client configuration.

Returns:

  • (Config) —

    The client configuration



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# File 'lib/langfuse/client.rb', line 26

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 151

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_dataset(name:, description: nil, metadata: nil) ⇒ DatasetClient

Create a new dataset

Examples:

dataset = client.create_dataset(name: "my-dataset", description: "QA evaluation set")

Parameters:

  • name (String) —

    Dataset name (required)

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

    Optional description

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

    Optional metadata hash

Returns:

Raises:



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# File 'lib/langfuse/client.rb', line 408

def create_dataset(name:, description: nil, metadata: nil)
  data = api_client.create_dataset(name: name, description: description, metadata: metadata)
  DatasetClient.new(data, client: self)
end

#create_dataset_item(dataset_name:, input: nil, expected_output: nil, metadata: nil, id: nil, source_trace_id: nil, source_observation_id: nil, status: nil) ⇒ DatasetItemClient

Create a new dataset item

rubocop:disable Metrics/ParameterLists

Examples:

item = client.create_dataset_item(
  dataset_name: "my-dataset",
  input: { query: "What is Ruby?" },
  expected_output: { answer: "A programming language" }
)

Parameters:

  • dataset_name (String) —

    Name of the dataset to add item to (required)

  • input (Object, nil) (defaults to: nil) —

    Input data for the item

  • expected_output (Object, nil) (defaults to: nil) —

    Expected output for evaluation

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

    Optional metadata

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

    Optional ID for upsert behavior

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

    Link to source trace

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

    Link to source observation

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

    Item status (:active or :archived)

Returns:

Raises:



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# File 'lib/langfuse/client.rb', line 463

def create_dataset_item(dataset_name:, input: nil, expected_output: nil,
                        metadata: nil, id: nil, source_trace_id: nil,
                        source_observation_id: nil, status: nil)
  data = api_client.create_dataset_item(
    dataset_name: dataset_name, input: input, expected_output: expected_output,
    metadata: metadata, id: id, source_trace_id: source_trace_id,
    source_observation_id: source_observation_id, status: status
  )
  DatasetItemClient.new(data, client: self)
end

#create_dataset_run_item(dataset_item_id:, run_name:, trace_id: nil, observation_id: nil, metadata: nil, run_description: nil) ⇒ Hash

Create a dataset run item (link a trace to a dataset item)

Parameters:

  • dataset_item_id (String) —

    Dataset item ID (required)

  • run_name (String) —

    Run name (required)

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

    Trace ID

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

    Observation ID

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

    Optional metadata

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

    Optional run description

Returns:

  • (Hash) —

    The created dataset run item data



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# File 'lib/langfuse/client.rb', line 544

def create_dataset_run_item(dataset_item_id:, run_name:, trace_id: nil,
                            observation_id: nil, metadata: nil, run_description: nil)
  api_client.create_dataset_run_item(
    dataset_item_id: dataset_item_id,
    run_name: run_name,
    trace_id: trace_id,
    observation_id: observation_id,
    metadata: metadata,
    run_description: run_description
  )
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 195

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, dataset_run_id: nil, config_id: nil) ⇒ 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)

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

    Optional dataset run ID to associate with the score

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

    Optional score config ID

Raises:

  • (ArgumentError) —

    if validation fails



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# File 'lib/langfuse/client.rb', line 307

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

#dataset_run_url(dataset_id:, dataset_run_id:) ⇒ String?

Generate URL for viewing a dataset run in Langfuse UI

Parameters:

  • dataset_id (String) —

    The dataset ID

  • dataset_run_id (String) —

    The dataset run ID

Returns:

  • (String, nil) —

    URL to view the dataset run, or nil if project ID unavailable



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# File 'lib/langfuse/client.rb', line 280

def dataset_run_url(dataset_id:, dataset_run_id:)
  project_url("datasets/#{dataset_id}/runs/#{dataset_run_id}")
end

#dataset_url(dataset_id) ⇒ String?

Generate URL for viewing a dataset in Langfuse UI

Parameters:

  • dataset_id (String) —

    The dataset ID

Returns:

  • (String, nil) —

    URL to view the dataset, or nil if project ID unavailable



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# File 'lib/langfuse/client.rb', line 271

def dataset_url(dataset_id)
  project_url("datasets/#{dataset_id}")
end

#delete_dataset_item(id) ⇒ nil

Note:

404 responses are treated as success to keep DELETE idempotent across retries

Delete a dataset item by ID

Examples:

client.delete_dataset_item("item-uuid-123")

Parameters:

  • id (String) —

    Dataset item ID

Returns:

  • (nil)

Raises:



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# File 'lib/langfuse/client.rb', line 530

def delete_dataset_item(id)
  api_client.delete_dataset_item(id)
  nil
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 383

def flush_scores
  @score_client.flush
end

#get_dataset(name) ⇒ DatasetClient

Fetch a dataset by name

Examples:

dataset = client.get_dataset("my-dataset")

Parameters:

  • name (String) —

    Dataset name (supports folder paths like “evaluation/qa-dataset”)

Returns:

Raises:



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# File 'lib/langfuse/client.rb', line 423

def get_dataset(name)
  data = api_client.get_dataset(name)
  DatasetClient.new(data, client: self)
end

#get_dataset_item(id) ⇒ DatasetItemClient

Fetch a dataset item by ID

Examples:

item = client.get_dataset_item("item-uuid-123")

Parameters:

  • id (String) —

    Dataset item ID

Returns:

Raises:



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# File 'lib/langfuse/client.rb', line 485

def get_dataset_item(id)
  data = api_client.get_dataset_item(id)
  DatasetItemClient.new(data, client: self)
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 80

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_dataset_items(dataset_name:, page: nil, limit: nil, source_trace_id: nil, source_observation_id: nil) ⇒ Array<DatasetItemClient>

List items in a dataset

When page is nil (default), auto-paginates to fetch all items. When page is provided, returns only that single page.

Examples:

items = client.list_dataset_items(dataset_name: "my-dataset", limit: 50)

Parameters:

  • dataset_name (String) —

    Name of the dataset (required)

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

    Optional page number for pagination

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

    Optional limit per page

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

    Filter by source trace ID

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

    Filter by source observation ID

Returns:

Raises:



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# File 'lib/langfuse/client.rb', line 506

def list_dataset_items(dataset_name:, page: nil, limit: nil,
                       source_trace_id: nil, source_observation_id: nil)
  filters = { dataset_name: dataset_name, source_trace_id: source_trace_id,
              source_observation_id: source_observation_id }

  items = if page
            fetch_dataset_items_page(page: page, limit: limit, **filters)
          else
            fetch_all_dataset_items(limit: limit, **filters)
          end

  items.map { |data| DatasetItemClient.new(data, client: self) }
end

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

List all datasets in the project

Examples:

datasets = client.list_datasets(page: 1, limit: 10)

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 dataset metadata hashes

Raises:



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# File 'lib/langfuse/client.rb', line 438

def list_datasets(page: nil, limit: nil)
  api_client.list_datasets(page: page, limit: limit)
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 114

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

#project_id ⇒ String?

Lazily-fetched project ID for URL generation

Fetches the project ID from the API on first access and caches it. Returns nil if the API call fails (URL generation is non-critical).

Returns:

  • (String, nil) —

    The Langfuse project ID



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# File 'lib/langfuse/client.rb', line 249

def project_id
  return @project_id if @project_id_fetched

  fetch_project_id
end

#run_experiment(name:, task:, data: nil, dataset_name: nil, description: nil, evaluators: [], run_evaluators: [], metadata: nil, run_name: nil) ⇒ ExperimentResult

Run an experiment against local data or a named dataset

rubocop:disable Metrics/ParameterLists

Parameters:

  • name (String) —

    Experiment/run name (required)

  • data (Array<Hash, DatasetItemClient>, nil) (defaults to: nil) —

    Local data items (each Hash with :input/:expected_output or “input”/“expected_output”; also accepts DatasetItemClient objects, e.g. when called from DatasetClient#run_experiment)

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

    Dataset name to fetch items from

  • task (Proc) —

    Callable receiving a single argument (the item). The item is a DatasetItemClient (when using dataset_name:) or ExperimentItem (when using data:). Tracing is handled automatically; use DatasetItemClient#run for direct span access.

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

    Optional run description

  • evaluators (Array<Proc>) (defaults to: []) —

    Item-level evaluators

  • run_evaluators (Array<Proc>) (defaults to: []) —

    Run-level evaluators

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

    Optional metadata

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

    Explicit run name (defaults to “name - timestamp”)

Returns:

Raises:

  • (ArgumentError) 


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# File 'lib/langfuse/client.rb', line 574

def run_experiment(name:, task:, data: nil, dataset_name: nil, description: nil,
                   evaluators: [], run_evaluators: [], metadata: nil, run_name: nil)
  raise ArgumentError, "Provide either data: or dataset_name:, not both" if data && dataset_name
  raise ArgumentError, "Provide data: or dataset_name:" unless data || dataset_name

  items = resolve_experiment_items(data, dataset_name)

  ExperimentRunner.new(
    client: self,
    name: name,
    items: items,
    task: task,
    evaluators: evaluators,
    run_evaluators: run_evaluators,
    metadata: metadata,
    description: description,
    run_name: run_name
  ).execute
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 339

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 365

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 392

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, nil) —

    URL to view the trace, or nil if project ID unavailable



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

def trace_url(trace_id)
  project_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 233

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

  build_prompt_client(prompt_data)
end