Enable Guardrails Metrics#

Use this minimal setup to enable metrics from IORails with the OpenTelemetry SDK and console output. LLMRails does not support OpenTelemetry metrics. Use this to verify metric emission locally before wiring up a production exporter.

Experimental Feature

Metrics currently require the opt-in IORails engine. Enable it either by constructing Guardrails(config, use_iorails=True) (the form used in this quickstart) or by setting NEMO_GUARDRAILS_IORAILS_ENGINE=1, which aliases the top-level LLMRails import to Guardrails. IORails is an early-release feature, and metric names can change as the OpenTelemetry GenAI semantic conventions evolve.

  1. Install the NeMo Guardrails library and the OpenTelemetry SDK.

    pip install "nemoguardrails[tracing]" opentelemetry-sdk

    The [tracing] extra installs opentelemetry-api, which is the only OpenTelemetry dependency the library itself takes.

  2. Save the following to metrics_example.py. The script issues a single request and exports metrics once per second to both stdout and metrics.json. The provider.shutdown() call flushes the metrics to disk. Long-running services typically do not need this call.

    # metrics_example.py
import asyncio

from opentelemetry import metrics
from opentelemetry.sdk.metrics import MeterProvider
from opentelemetry.sdk.metrics.export import (
    ConsoleMetricExporter,
    PeriodicExportingMetricReader,
)
from opentelemetry.sdk.resources import Resource

from nemoguardrails import Guardrails, RailsConfig
# Configure the OpenTelemetry MeterProvider BEFORE constructing Guardrails so
# the engine resolves a real meter on first metric emission.  Two readers
# are attached to the same provider: one writes to stdout for live
# inspection, the other writes to ``metrics.json``.
resource = Resource.create({"service.name": "guardrails-quickstart"})
metrics_file = open("metrics.json", "w")
console_reader = PeriodicExportingMetricReader(
    ConsoleMetricExporter(),
    export_interval_millis=1000,
)
file_reader = PeriodicExportingMetricReader(
    ConsoleMetricExporter(out=metrics_file),
    export_interval_millis=1000,
)
provider = MeterProvider(
    resource=resource,
    metric_readers=[console_reader, file_reader],
)
metrics.set_meter_provider(provider)

# Use Configuration with metrics enabled.
config_yaml = """
models:
  - type: main
    engine: openai
    model: gpt-4o-mini

metrics:
  enabled: true
"""

config = RailsConfig.from_content(yaml_content=config_yaml)

async def main() -> None:
    # use_iorails=True selects the IORails engine (the only engine that emits
    # metrics). require_iorails=True raises a ValueError if the config is
    # incompatible with IORails.
    async with Guardrails(config, use_iorails=True, require_iorails=True) as rails:
        response = await rails.generate_async(
            messages=[{"role": "user", "content": "Write an essay with historical context on NVIDIA"}],
        )
        print(f"Response: {response}")

try:
    asyncio.run(main())
finally:
    # Flush and tear down the reader so the final batch reaches the exporter
    # before the process exits, then close the metrics file.
    provider.shutdown()
    metrics_file.close()

  3. Run the script.

    python metrics_example.py

  4. Post-process the metrics JSON file.

    metrics.json contains one JSON document per export interval, concatenated. The following command reads every interval into an array and returns the final object, which is the cumulative state after the request completed.

    jq -s 'last | .resource_metrics[].scope_metrics[].metrics[]
       | select(.name=="gen_ai.client.token.usage")
       | .data.data_points[]
       | {type: .attributes."gen_ai.token.type", count, sum}' metrics.json

    Example output (exact output token counts can vary):

    {
  "type": "input",
  "count": 1,
  "sum": 15
}
{
  "type": "output",
  "count": 1,
  "sum": 1033
}

    Each object is one aggregation of the gen_ai.client.token.usage histogram. The fields are:

    • type: Value of the required gen_ai.token.type label. Values are either input or output.

    • count: Number of observations recorded for this token type. Each LLM call records one input observation and one output observation, giving count: 1 per type.

    • sum: Total tokens across those observations.

Important

The host application is responsible for configuring a MeterProvider. If you construct LLMRails(config) with metrics.enabled: true but no MeterProvider is set, the OpenTelemetry API returns a no-op meter and silently discards every metric emission. The library does not log a warning. Always set the MeterProvider before constructing LLMRails.

Next Steps#

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