---
title: Observability
description: Metrics, tracing, and monitoring for your AI gateway.
---

## Metrics Extension

The built-in metrics extension tracks operational counters:

```go
import "github.com/xraph/nexus/observability"

metrics := observability.NewMetricsExtension()
gw := nexus.New(
    nexus.WithExtension(metrics),
)

// Read counters
metrics.RequestsCompleted.Value() // int64
metrics.ProviderFailures.Value()
metrics.GuardrailBlocks.Value()
```

## Tracing

Add OpenTelemetry spans to every request:

```go
nexus.WithTracer(otelTracer)
```

The tracing middleware (priority 10) creates spans with:
- Request model and provider
- Tenant ID
- Token counts
- Cache hit/miss status

## Response Headers

Every response includes diagnostic headers:

| Header | Value |
|--------|-------|
| `X-Nexus-Request-ID` | Unique request identifier |
| `X-Nexus-Provider` | Provider that served the request |
| `X-Nexus-Cache` | `HIT` or `MISS` |
| `X-Nexus-Latency` | Processing time in milliseconds |