Attach user feedback and custom quality scores (numeric, categorical, boolean, text) to a Langfuse trace or observation via the Scores API and SDK

Documented steps

1. Decide the score's scope. Always pass `trace_id`/`traceId`; add `observation_id`/`observationId` only when the score applies to one specific span or generation rather than the whole interaction.
2. Optionally create a Score Config first in the UI under Settings > Scores. This enforces a schema (min/max for numeric, allowed category labels), is required for the score to appear in the UI Annotate flow, and gives you a `config_id` for server-side validation.
3. Numeric score in Python: `langfuse.create_score(name="correctness", value=0.9, trace_id="trace_id_here", data_type="NUMERIC")`. The value must respect any min/max on the linked config.
4. Boolean score: `langfuse.create_score(trace_id=trace_id, name="is_correct", value=1, data_type="BOOLEAN")`. Boolean scores must be provided as a float where 1 is true and 0 is false; the v3 Scores API returns them as an actual boolean on read.
5. Categorical score: `langfuse.create_score(trace_id=trace_id, name="tone", value="friendly", data_type="CATEGORICAL")`. The string must match one of the config's defined category labels when a config is attached. A separate TEXT data type exists for free-form qualitative notes.
6. From inside an active span or generation, prefer the shorthand helpers over rebuilding IDs: `langfuse.score_current_span(name="helpfulness", value=1, data_type="BOOLEAN")` or `langfuse.score_current_trace(...)`, or call `.score()`/`.score_trace()` on the span object.
7. In JS/TS: `langfuse.score.create({ traceId: message.traceId, name: "correctness", value: 0.9, dataType: "NUMERIC" })`. In serverless or edge runtimes, `await langfuse.flush()` afterwards so the score is sent before the process exits.
8. For feedback pipelines outside your app backend, call the REST API directly: `curl -X POST https://cloud.langfuse.com/api/public/scores -u "$PUBLIC_KEY:$SECRET_KEY" -H 'Content-Type: application/json' -d '{"traceId":"...","name":"user_feedback","value":1,"dataType":"BOOLEAN"}'`. Use the regional host that matches your project.
9. Verified against current official docs on 2026-07-29: https://langfuse.com/docs/evaluation/evaluation-methods/custom-scores , https://langfuse.com/docs/evaluation/evaluation-methods/data-model