What values can the observation level have?

The level of an observation is one of four strings: DEBUG, DEFAULT, WARNING, or ERROR. Langfuse stores and returns these strings, not numbers, in the API, exports, and the UI. Filter by level with the level query parameter of the Observations API v2.

When you ingest OpenTelemetry spans, Langfuse sets the level as follows:

• From the langfuse.observation.level attribute, if present. Common aliases are mapped case-insensitively: TRACE and VERBOSE become DEBUG; INFO, LOG, NOTICE, OK, and SUCCESS become DEFAULT; WARN becomes WARNING; FATAL and CRITICAL become ERROR.
• Otherwise from the span status: a span with status ERROR gets level ERROR, every other span gets DEFAULT.

See Log levels.

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