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

# 02 basic setup

# Basic Setup

The smallest useful setup is:

1. create a `TraceRegistry`
2. create an exporter
3. create `Telemetry`
4. open a root span
5. add logs or child spans
6. complete the span
7. call `flush()`

## Minimal Example

```php theme={null}
use Cognesy\Telemetry\Adapters\OTel\OtelExporter;
use Cognesy\Telemetry\Application\Registry\TraceRegistry;
use Cognesy\Telemetry\Application\Telemetry;
use Cognesy\Telemetry\Domain\Value\AttributeBag;

$telemetry = new Telemetry(
    registry: new TraceRegistry(),
    exporter: new OtelExporter(),
);

$telemetry->openRoot(
    key: 'run',
    name: 'demo.run',
    attributes: AttributeBag::fromArray([
        'component' => 'demo',
    ]),
);

$telemetry->log(
    key: 'run',
    name: 'demo.step',
    attributes: AttributeBag::fromArray([
        'status' => 'ok',
    ]),
);

$telemetry->complete('run');
$telemetry->flush();
// @doctest id="a9fc"
```

## Adding Child Spans

Use `openChild()` when a unit of work should sit under another span:

```php theme={null}
$telemetry->openRoot('request', 'http.request');
$telemetry->openChild('llm', 'request', 'llm.inference');

$telemetry->complete('llm');
$telemetry->complete('request');
$telemetry->flush();
// @doctest id="6a60"
```

The keys `request` and `llm` are local registry keys. They do not have to match
the span name.

## Exporting To More Than One Backend

Use `CompositeTelemetryExporter` when you want more than one output:

```php theme={null}
use Cognesy\Telemetry\Adapters\OTel\OtelExporter;
use Cognesy\Telemetry\Application\Exporter\CompositeTelemetryExporter;
use Cognesy\Telemetry\Application\Registry\TraceRegistry;
use Cognesy\Telemetry\Application\Telemetry;

$telemetry = new Telemetry(
    registry: new TraceRegistry(),
    exporter: new CompositeTelemetryExporter([
        new OtelExporter(),
        $logfireExporter,
        $langfuseExporter,
    ]),
);
// @doctest id="3536"
```

## Notes

* `flush()` matters. Exporters buffer observations until you call it.
* `OtelExporter()` without a transport is useful for local debugging and tests.