> ## Documentation Index
> Fetch the complete documentation index at: https://docs.trynexus.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Configuration

> Configure Nexus DB connections and trigger behavior

Nexus writes events to PostgreSQL and optionally triggers a follow-up endpoint after root-chain completion.

## Database URL

You can set the DB URL in two common ways:

* pass `db_url` directly to `NexusClient` / `LangHandler`
* rely on library config helpers (`get_db_url()` / `set_db_url()`)

```python theme={null}
from nexus_library.nexus_core import NexusClient

client = NexusClient(
    api_key="00000000-0000-0000-0000-000000000000",
    db_url="postgresql://user:pass@host/db",
)
```

## Trigger URL

LangChain tracing can call a trigger endpoint after root chain completion or failure:

* `POST {trigger_url}/catch_route_manual`

The URL is read through `get_trigger_url()`.

## Storage contract

The library expects an `agent_logs` table with at least:

* UUIDs for `run_id`, `user_id`, and optional `parent_run_id`
* text for `trace_id`, `event_type`, and `name`
* JSONB fields for `input` and `output`
* nullable text for `error`

## Security guidance

<Warning>
  Do not rely on hardcoded credentials in source code for production usage. Prefer environment-driven secrets and managed secret stores.
</Warning>

* rotate credentials regularly
* use least-privilege DB roles
* separate dev and prod storage backends