Langfuse Setup

The simplest Langfuse setup uses:

• LangfuseConfig
• LangfuseHttpTransport
• LangfuseExporter
• Telemetry

Minimal Example

use Cognesy\Telemetry\Adapters\Langfuse\LangfuseConfig;
use Cognesy\Telemetry\Adapters\Langfuse\LangfuseExporter;
use Cognesy\Telemetry\Adapters\Langfuse\LangfuseHttpTransport;
use Cognesy\Telemetry\Application\Registry\TraceRegistry;
use Cognesy\Telemetry\Application\Telemetry;

$telemetry = new Telemetry(
    registry: new TraceRegistry(),
    exporter: new LangfuseExporter(
        transport: new LangfuseHttpTransport(new LangfuseConfig(
            baseUrl: $_ENV['LANGFUSE_BASE_URL'],
            publicKey: $_ENV['LANGFUSE_PUBLIC_KEY'],
            secretKey: $_ENV['LANGFUSE_SECRET_KEY'],
        )),
    ),
);

Environment Variables

The examples use:

• LANGFUSE_BASE_URL
• LANGFUSE_PUBLIC_KEY
• LANGFUSE_SECRET_KEY

Reference Example

The inline reference example is:

• examples/A03_Troubleshooting/TelemetryLangfuse/run.php

Agent Runtime Example

The working agent example is:

• examples/D05_AgentTroubleshooting/TelemetryLangfuse/run.php

That example shows the full pattern:

1. create telemetry
2. create a shared event dispatcher
3. attach RuntimeEventBridge
4. install runtime projectors
5. execute the agent
6. call $hub->flush()

Subagent Example

For nested telemetry across parent and child agents, see:

• examples/D05_AgentTroubleshooting/SubagentTelemetryLangfuse/run.php

Notes

• Langfuse uses the base URL and sends traces to /api/public/otel/v1/traces
• request-scoped traces can fall back to request ids as session.id
• if you get a 4xx response, check the base URL and keys first