Query Data via SDKs
Langfuse is open-source and data tracked with Langfuse is open. You can query data via: SDKs and API. For export functionality, see Export Data.
Common use cases:
- Train or fine-tune models on the production traces in Langfuse. E.g. to create a small model after having used a large model in production for a specific use case.
- Collect few-shot examples to improve quality of output.
- Programmatically create datasets.
If you are new to Langfuse, we recommend familiarizing yourself with the Langfuse data model.
New data is typically available for querying within 15-30 seconds of ingestion, though processing times may vary at times. Please visit status.langfuse.com if you encounter any issues.
SDKs
Via the SDKs for Python and JS/TS you can easily query the API without having to write the HTTP requests yourself.
If you need aggregated metrics (e.g., counts, costs, usage) rather than individual entities, consider the Metrics API. It is optimized for aggregate queries and higher rate limits.
pip install langfusefrom langfuse import get_client
langfuse = get_client() # uses environment variables to authenticateThe api namespace is auto-generated from the Public API (OpenAPI). Method names mirror REST resources and support filters and pagination.
Traces
traces = langfuse.api.trace.list(limit=100, user_id="user_123", tags=["production"]) # pagination via cursor
trace = langfuse.api.trace.get("traceId")Observations
observations = langfuse.api.observations.get_many(trace_id="abcdef1234", type="GENERATION", limit=100)
observation = langfuse.api.observations.get("observationId")Sessions
sessions = langfuse.api.sessions.list(limit=50)Scores
langfuse.api.score_v_2.get(score_ids = "ScoreId")Prompts
Please refer to the prompt management documentation on fetching prompts.
Datasets
# Namespaces:
# - langfuse.api.datasets.*
# - langfuse.api.dataset_items.*
# - langfuse.api.dataset_run_items.*Metrics
query = """
{
"view": "traces",
"metrics": [{"measure": "count", "aggregation": "count"}],
"dimensions": [{"field": "name"}],
"filters": [],
"fromTimestamp": "2025-05-01T00:00:00Z",
"toTimestamp": "2025-05-13T00:00:00Z"
}
"""
langfuse.api.metrics.metrics(query = query)Async equivalents
# All endpoints are also available as async under `async_api`:
trace = await langfuse.async_api.trace.get("traceId")
traces = await langfuse.async_api.trace.list(limit=100)Common filtering & pagination
- limit, cursor (pagination)
- time range filters (e.g., start_time, end_time)
- entity filters: user_id, session_id, trace_id, type, name, tags, level, etc.
See the Public API for the exact parameters per resource.