agent-observability

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---
name: agent-observability
description: Instrument AI agents with tracing, token metrics, latency, and cost visibility. Use for reliability and debugging.
license: MIT
metadata:
  author: devops-skills
  version: "2.0"
---

# Agent Observability

Monitor AI agent behavior with logs, traces, metrics, and cost telemetry. This skill covers the full observability stack for LLM-powered applications: from raw Prometheus counters to Grafana dashboards, OpenTelemetry tracing, structured logging, cost tracking, SLO definition, and PII redaction.

---

## When to Use

Apply this skill whenever you operate:

- **Autonomous AI agents** that make multi-step tool calls (e.g., coding agents, support agents, data-pipeline agents).
- **LLM-backed APIs** serving chat completions, summarisation, or classification behind a REST or gRPC gateway.
- **RAG pipelines** where a retriever fetches context from a vector store before prompting a model.
- **Multi-agent orchestrations** (crew-style or graph-based) where several agents collaborate on a single task.
- **Batch inference jobs** that process thousands of prompts against a model endpoint.

Key signals that you need this skill:

1. You cannot answer "what is p95 latency for agent responses this week?"
2. You have no per-request cost attribution.
3. Debugging a bad agent response requires grepping raw application logs.
4. You have no alerting on token-usage spikes or elevated error rates.

---

## Core Metrics

Define these metrics at the application layer. All examples use the Prometheus client library naming conventions.

### Latency

```python
from prometheus_client import Histogram

# Total end-to-end latency for a full agent turn (user prompt -> final response)
AGENT_LATENCY = Histogram(
    "agent_request_duration_seconds",
    "End-to-end latency of an agent request",
    labelnames=["agent_name", "model", "status"],
    buckets=(0.25, 0.5, 1, 2, 5, 10, 30, 60, 120),
)

# Latency of a single LLM API call (one completion request)
LLM_CALL_LATENCY = Histogram(
    "llm_call_duration_seconds",
    "Latency of an individual LLM API call",
    labelnames=["model", "provider", "stream"],
    buckets=(0.1, 0.25, 0.5, 1, 2, 5, 10, 30),
)

# Latency of tool/function calls executed by the agent
TOOL_CALL_LATENCY = Histogram(
    "agent_tool_call_duration_seconds",
    "Latency of a tool call executed by the agent",
    labelnames=["tool_name", "agent_name", "status"],
    buckets=(0.05, 0.1, 0.25, 0.5, 1, 2, 5, 10),
)
```

### Token Usage

```python
from prometheus_client import Counter, Histogram

PROMPT_TOKENS = Counter(
    "llm_prompt_tokens_total",
    "Total prompt tokens sent to the model",
    labelnames=["model", "agent_name"],
)

COMPLETION_TOKENS = Counter(
    "llm_completion_tokens_total",
    "Total completion tokens received from the model",
    labelnames=["model", "agent_name"],
)

CACHED_TOKENS = Counter(
    "llm_cached_tokens_total",
    "Prompt tokens served from KV-cache (provider-reported)",
    labelnames=["model", "agent_name"],
)

TOKENS_PER_REQUEST = Histogram(
    "llm_tokens_per_request",
    "Total tokens (prompt + completion) per request",
    labelnames=["model", "agent_name"],
    buckets=(100, 500, 1000, 2000, 4000, 8000, 16000, 32000, 64000, 128000),
)
```

### Cost

```python
from prometheus_client import Counter

LLM_COST = Counter(
    "llm_cost_dollars_total",
    "Estimated cost in USD for LLM usage",
    labelnames=["model", "agent_name", "cost_type"],  # cost_type: prompt | completion
)
```

### Tool Calls

```python
from prometheus_client import Counter

TOOL_CALLS_TOTAL = Counter(
    "agent_tool_calls_total",
    "Total tool calls made by agents",
    labelnames=["tool_name", "agent_name", "status"],  # status: success | error | timeout
)
```

### Errors and Retries

```python
from prometheus_client import Counter, Gauge

LLM_ERRORS = Counter(
    "llm_errors_total",
    "Errors returned by the LLM provider",
    labelnames=["model", "provider", "error_ty