OpenTelemetry Tracing

Export distributed traces from Mellea using OpenTelemetry semantic conventions.

Prerequisites: Metrics and Telemetry introduces the environment variables and trace scopes. This page focuses on exporting traces to external backends and interpreting the span data they contain.

Mellea instruments both user-facing operations and LLM backend calls using the OpenTelemetry Gen-AI Semantic Conventions. When tracing is enabled, every m.act(), @generative call, and LLM request produces spans you can inspect in Jaeger, Grafana Tempo, Honeycomb, or any OTLP-compatible backend.

Note: Tracing is an optional feature. Mellea works normally without it. All telemetry calls are no-ops when the [telemetry] extra is not installed.

Install and enable tracing

Install the telemetry extra:

pip install "mellea[telemetry]"

Enable one or both trace scopes via environment variables:

export MELLEA_TRACE_APPLICATION=true   # user-facing operations
export MELLEA_TRACE_BACKEND=true       # LLM calls and token usage

Run your script. If no OTLP endpoint is configured, spans are silently discarded. To verify instrumentation immediately, add console output:

export MELLEA_TRACE_CONSOLE=true
python your_script.py

Spans print to stdout in OpenTelemetry’s default text format.

Configuring an OTLP exporter

Set OTEL_EXPORTER_OTLP_ENDPOINT to any OTLP-compatible endpoint. Mellea uses the gRPC OTLP exporter, so the endpoint must accept gRPC (default port 4317).

Jaeger

docker run -d --name jaeger \
  -p 4317:4317 \
  -p 16686:16686 \
  jaegertracing/all-in-one:latest

export MELLEA_TRACE_APPLICATION=true
export MELLEA_TRACE_BACKEND=true
export OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4317
export OTEL_SERVICE_NAME=my-mellea-app

python your_script.py

Open http://localhost:16686 to browse traces.

Grafana Tempo

export MELLEA_TRACE_APPLICATION=true
export MELLEA_TRACE_BACKEND=true
export OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4317
export OTEL_SERVICE_NAME=my-mellea-app

python your_script.py

Grafana Tempo accepts OTLP on port 4317 by default. Point a Grafana datasource at Tempo’s HTTP endpoint (http://localhost:3200) and use the Explore panel to query by service name.

Other backends

Any OTLP-compatible backend works with the same environment variables: Honeycomb, Datadog, New Relic, AWS X-Ray (via the OTEL collector), and Google Cloud Trace all accept OTLP over gRPC.

Checking trace status programmatically

from mellea.telemetry import (
    is_application_tracing_enabled,
    is_backend_tracing_enabled,
)

print(f"Application tracing: {is_application_tracing_enabled()}")
print(f"Backend tracing:     {is_backend_tracing_enabled()}")

What spans Mellea emits

Mellea has two independent trace scopes. Enable them separately to reduce noise during debugging.

Application spans (mellea.application)

Application spans cover user-facing Mellea operations. They appear whenever you call m.act(), m.instruct(), m.chat(), or a @generative function.

Attribute	Description
mellea.backend	Backend class name (e.g., OllamaModelBackend)
mellea.action_type	Component class being executed (e.g., Instruction)
mellea.context_size	Length of the context at call time
mellea.has_format	Whether a format constraint was specified
sampling_success	Whether the sampling strategy succeeded
num_generate_logs	Number of generation attempts (>1 means retries occurred)
response	Model response truncated to 500 characters

Backend spans (mellea.backend)

Backend spans cover individual LLM API calls. They follow the OpenTelemetry Gen-AI Semantic Conventions.

Attribute	Description
gen_ai.system	Backend system name mapped from class (e.g., ollama, openai)
gen_ai.request.model	Model ID requested
gen_ai.operation.name	"chat" for generate_from_context; "text_completion" for generate_from_raw
gen_ai.usage.input_tokens	Input tokens consumed
gen_ai.usage.output_tokens	Output tokens generated
gen_ai.usage.total_tokens	Total tokens (input + output)
gen_ai.response.finish_reasons	List of finish reasons (e.g., ["stop"])
gen_ai.response.id	Response identifier from the backend

Span hierarchy

When both scopes are active, backend spans nest inside application spans:

session_context           (mellea.application)
├── aact                  (mellea.application)
│   │                     [mellea.action_type=Instruction]
│   │                     [mellea.backend=OllamaModelBackend]
│   ├── chat              (mellea.backend)
│   │                     [gen_ai.system=ollama]
│   │                     [gen_ai.request.model=granite4:micro]
│   │                     [gen_ai.usage.input_tokens=150]
│   │                     [gen_ai.usage.output_tokens=42]
│   └── requirement_validation  (mellea.application)
└── aact                  (mellea.application)
    └── chat              (mellea.backend)
                          [gen_ai.system=openai]
                          [gen_ai.request.model=gpt-4o]

Reading traces in a typical agent run

When you open a trace in your backend, look for these patterns:

High input token counts on early spans. A single aact span with gen_ai.usage.input_tokens much larger than expected usually means the context has accumulated many previous messages. Use prefix caching to reduce cost.

Repeated requirement_validation spans beneath one aact. The value of num_generate_logs in the parent span tells you how many retries occurred. If the model keeps retrying, read the response attribute on each attempt to understand why validation is failing.

Long gaps between spans. A gap between the start of a backend chat span and the next application span usually indicates time spent waiting for the LLM. This is normal for large models but worth tracking across deploys.

gen_ai.response.finish_reasons containing "length". The model hit the maximum output token limit and was cut off. Increase max_tokens in your backend options or shorten your prompts.

Full working example

The example at docs/examples/telemetry/telemetry_example.py runs a session with instruct(), @generative, and m.chat() and prints trace status to stdout. Run it to verify your setup:

export MELLEA_TRACE_APPLICATION=true
export MELLEA_TRACE_BACKEND=true
export MELLEA_TRACE_CONSOLE=true
uv run python docs/examples/telemetry/telemetry_example.py

Disabling tracing

Tracing is disabled by default. If you have set the environment variables globally and need to turn tracing off for a test run or performance measurement, unset or set them to false:

export MELLEA_TRACE_APPLICATION=false
export MELLEA_TRACE_BACKEND=false
python your_script.py

For programmatic control in tests, override the environment before importing Mellea — Mellea reads the environment at import time:

import os

os.environ["MELLEA_TRACE_APPLICATION"] = "false"
os.environ["MELLEA_TRACE_BACKEND"] = "false"

import mellea  # noqa: E402

Warning: Setting the environment variables after mellea.telemetry has been imported has no effect. The tracing module reads the variables once at module load time and caches the result.

Tip: In pytest, use a session-scoped fixture to set environment variables before any test imports Mellea, or use monkeypatch.setenv combined with importlib.reload(mellea.telemetry.tracing) to reset state between tests.

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Next steps

• Metrics and Telemetry — enable metrics collection alongside tracing, and learn how to instrument your own code with counters and histograms.
• Evaluate with LLM-as-a-Judge — add automated quality evaluation to your pipeline and correlate evaluation results with trace data.