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

# Telemetry

> Emit structured logs, traces, OTLP signals, and privacy-safe audit events.

Harnest provides the same logging and tracing API for ADK and LangGraph.

| Signal            | Use it for                | Default destination         |
| ----------------- | ------------------------- | --------------------------- |
| Structured logs   | Searchable runtime events | JSON on stderr              |
| Traces            | Timing and causality      | Disabled until configured   |
| Audit events      | Durable mutation outcomes | Configured OTEL destination |
| Playground traces | Local debugging           | Process memory              |

## Add logs and spans

```python theme={null}
from harnest.logging import get_logger
from harnest.tracing import span, traced

logger = get_logger("catalog").bind(component="search")


@traced("catalog.lookup", attributes={"catalog.kind": "products"})
def lookup(query: str):
    with span("catalog.rank", candidate_count=12):
        logger.info("catalog.lookup.completed", result_count=3)
        return ["one", "two", "three"]
```

Logs inside a span carry its trace and span IDs.

## Configure OTLP

```bash theme={null}
export OTEL_SERVICE_NAME=support-agent
export OTEL_EXPORTER_OTLP_ENDPOINT=http://127.0.0.1:4318
export OTEL_EXPORTER_OTLP_PROTOCOL=http/protobuf
export HARNEST_LOG_LEVEL=INFO
harnest serve support-agent
```

| Property                      | Purpose                  |
| ----------------------------- | ------------------------ |
| `OTEL_SERVICE_NAME`           | Service identity         |
| `OTEL_EXPORTER_OTLP_ENDPOINT` | Collector endpoint       |
| `OTEL_EXPORTER_OTLP_PROTOCOL` | Export protocol          |
| `HARNEST_LOG_LEVEL`           | Minimum log level        |
| `HARNEST_LOG_CONSOLE=false`   | Disable JSON stderr logs |

Standard per-signal endpoints, headers, timeouts, compression, resources, and sampling variables also work. Keep exporter credentials in deployment secrets. Use a Collector for translation or fan-out.

## Privacy boundary

| Recorded by default                        | Not recorded by default      |
| ------------------------------------------ | ---------------------------- |
| Operation names and outcomes               | Prompts and responses        |
| Timing fields with a bounded set of values | Credentials and headers      |
| Correlated failures                        | Raw session IDs and payloads |

The playground trace inspector is bounded, process-local debug state—not an audit store. Runtime mutations emit audit signals after commit. CLI and compiler file changes are outside this runtime audit boundary.