Introduction

Python API surface for Nexus instrumentation

Nexus exposes a Python-first API for trace logging.

Core modules

• NexusClient and Span for manual instrumentation.
• LangHandler for LangChain callback instrumentation.
• config helpers for DB and trigger URLs.

Data model written to storage

Both manual spans and LangChain callbacks map to rows with these key fields:

• run_id
• user_id
• trace_id
• parent_run_id
• event_type
• name
• input
• output
• error

Reference pages

NexusClient + Span

Constructor behavior, span lifecycle, flush, and tree helpers.

LangHandler

Callback hooks, event mapping, and root-chain trigger behavior.