custom-metrics — Claude Code skill: what it does, how to install

---
name: custom-metrics
description: "Create, track, retrieve, update, and delete custom business metrics for configs. Covers full lifecycle: define metric kinds via API, emit events via SDK, and query results."
license: Apache-2.0
compatibility: Requires the LaunchDarkly server SDK and a LaunchDarkly API token with the `writer` role for metric management.
metadata:
  author: launchdarkly
  version: "1.0.0-experimental"
---

# Custom Metrics for Configs

Full lifecycle management of custom business metrics: create metric definitions via API, track events via SDK, retrieve metric data, and manage metrics programmatically.

## Prerequisites

- LaunchDarkly SDK initialized (see `sdk`)
- LaunchDarkly API token with `writer` role for metric management
- Understanding of built-in agent metrics (see `built-in-metrics`)

## API Access

Prefer the LaunchDarkly MCP server tools: they authenticate via OAuth and need no token. If a step has no MCP equivalent and you must call the REST API directly, ask the user to paste an API access token for this session and substitute it for `{api_token}` in the examples below. Do not search environment variables, `.env` files, or agent/MCP config files for credentials.

## Metrics Lifecycle Overview

| Step | Method | Purpose |
|------|--------|---------|
| 1. Create | API | Define metric in LaunchDarkly |
| 2. Track | SDK | Send events to the metric |
| 3. Get | API | Retrieve metric definition/data |
| 4. Update | API | Modify metric properties |
| 5. Delete | API | Remove metric |

## 1. Create Metric (API)

**Required fields for numeric custom metrics:**
- `successCriteria` - Must be one of: `"HigherThanBaseline"`, `"LowerThanBaseline"`
- `unit` - e.g., `"count"`, `"percent"`, `"milliseconds"`

The API will return `400 Bad Request` if these are missing for numeric metrics.

```python
import requests
import os

def create_metric(
    project_key: str,
    metric_key: str,
    name: str,
    kind: str = "custom",
    is_numeric: bool = True,
    unit: str = "count",
    success_criteria: str = "HigherThanBaseline",
    event_key: str = None,
    description: str = None
):
    """Create a new metric definition in LaunchDarkly."""
    API_TOKEN = "{api_token}"  # token the user provided for this session

    url = f"https://app.launchdarkly.com/api/v2/metrics/{project_key}"

    payload = {
        "key": metric_key,
        "name": name,
        "kind": kind,
        "isNumeric": is_numeric,
        "eventKey": event_key or metric_key
    }

    # Unit and successCriteria are required for numeric custom metrics
    if is_numeric and kind == "custom":
        payload["unit"] = unit
        payload["successCriteria"] = success_criteria

    if description:
        payload["description"] = description

    headers = {
        "Authorization": API_TOKEN,
        "Content-Type": "application/json"
    }

    response = requests.post(url, json=payload, headers=headers)

    if response.status_code == 201:
        print(f"[OK] Created metric: {metric_key}")
        return response.json()
    elif response.status_code == 409:
        print(f"[INFO] Metric already exists: {metric_key}")
        return None
    else:
        print(f"[ERROR] Failed to create metric: {response.status_code}")
        print(f"        {response.text}")
        return None
```

**Metric Kinds:**
- `custom` - Track any event (most common for agent metrics)
- `pageview` - Track page views
- `click` - Track click events

**Success Criteria** (for numeric metrics):
- `HigherThanBaseline` - Higher values are better (e.g., revenue, satisfaction)
- `LowerThanBaseline` - Lower values are better (e.g., errors, latency)

**Common Units:**
- `count` - Generic count
- `milliseconds` - Time duration
- `percent` - Percentage values
- `dollars` - Currency

## 2. Track Events (SDK)

Once the metric is created, track events using the SDK:

```python
from ldclient import Context
from ldclient.config import Config
import ldclient

# Initialize (see sdk for details)
ldclient.set_config(Config("your-sdk-key"))
ld_client = ldclient.get()

def track_metric(ld_client, user_id: str, metric_key: str, value: float, data: dict = None):
    """Track an event to a metric."""
    context = Context.builder(user_id).build()

    ld_client.track(
        metric_key,
        context,
        data=data,
        metric_value=value
    )
```

### Common Tracking Patterns

```python
def track_conversion(ld_client, user_id: str, amount: float, config_key: str):
    """Track a conversion event with revenue."""
    context = Context.builder(user_id).build()

    ld_client.track(
        "business.conversion",
        context,
        data={"configKey": config_key, "category": "electronics"},
        metric_value=amount
    )

def track_task_success(ld_client, user_id: str, task_type: str, success: bool):
    """Track task completion success/failure."""
    context = Context.builder(user_id).build()

    ld_client.track(
        "task.success_rate",
        context,
        data={"taskType": task_type},
        metric_value=1.0 if success else 0.0
    )

def track_satisfaction(ld_client, user_id: str, score: float, feedback_type: str):
    """Track user satisfaction (0-100 scale)."""
    context = Context.builder(user_id).build()

    ld_client.track(
        "user.satisfaction",
        context,
        data={"feedbackType": feedback_type},
        metric_value=score
    )

    # Track negative feedback separately for alerts
    if score < 50:
        ld_client.track(
            "user.negative_feedback",
            context,
            metric_value=1.0
        )

def track_revenue(ld_client, user_id: str, revenue: float, source: str):
    """Track revenue generated after agent interaction."""
    context = Context.builder(user_id).set("tier", "premium").build()

    if revenue > 0:
        ld_client.track(
            "revenue.impact",
            context,
            data={"source": source},
            metric_value=revenue
        )
```

## 3. Get Metrics (API)

### Get Single Metric

```python
def get_metric(project_key: str, metric_key: str):
    """Get a single metric definition."""
    API_TOKEN = "{api_token}"  # token the user provided for this session

    url = f"https://app.launchdarkly.com/api/v2/metrics/{project_key}/{metric_key}"

    headers = {"Authorization": API_TOKEN}

    response = requests.get(url, headers=headers)

    if response.status_code == 200:
        metric = response.json()
        print(f"[OK] Metric: {metric['key']}")
        print(f"     Name: {metric.get('name', 'N/A')}")
        print(f"     Kind: {metric.get('kind', 'N/A')}")
        print(f"     Numeric: {metric.get('isNumeric', False)}")
        print(f"     Event Key: {metric.get('eventKey', 'N/A')}")
        return metric
    elif response.status_code == 404:
        print(f"[INFO] Metric not found: {metric_key}")
        return None
    else:
        print(f"[ERROR] Failed to get metric: {response.status_code}")
        return None
```

### List All Metrics

```python
def list_metrics(project_key: str, limit: int = 20):
    """List all metrics in a project."""
    API_TOKEN = "{api_token}"  # token the user provided for this session

    url = f"https://app.launchdarkly.com/api/v2/metrics/{project_key}"

    headers = {"Authorization": API_TOKEN}
    params = {"limit": limit}

    response = requests.get(url, headers=headers, params=params)

    if response.status_code == 200:
        data = response.json()
        metrics = data.get("items", [])
        print(f"[OK] Found {len(metrics)} metrics:")
        for metric in metrics:
            numeric = "numeric" if metric.get("isNumeric") else "non-numeric"
            print(f"     - {metric['key']} ({metric.get('kind', 'custom')}, {numeric})")
        return metrics
    else:
        print(f"[ERROR] Failed to list metrics: {response.status_code}")
        return None
```

## 4. Update Metric (API)

```python
def update_metric(project_key: str, metric_key: str, updates: list):
    """
    Update a metric using JSON Patch operations.

    Args:
        updates: List of patch operations, e.g.:
            [{"op": "replace", "path": "/name", "value": "New Name"}]
    """
    API_TOKEN = "{api_token}"  # token the user provided for this session

    url = f"https://app.launchdarkly.com/api/v2/metrics/{project_key}/{metric_key}"

    headers = {
        "Authorization": API_TOKEN,
        "Content-Type": "application/json"
    }

    response = requests.patch(url, json=updates, headers=headers)

    if response.status_code == 200:
        print(f"[OK] Updated metric: {metric_key}")
        return response.json()
    elif response.status_code == 404:
        print(f"[ERROR] Metric not found: {metric_key}")
        return None
    else:
        print(f"[ERROR] Failed to update metric: {response.status_code}")
        print(f"        {response.text}")
        return None

# Example: Update metric name and description
def rename_metric(project_key: str, metric_key: str, new_name: str, new_description: str = None):
    """Rename a metric and optionally update description."""
    updates = [
        {"op": "replace", "path": "/name", "value": new_name}
    ]
    if new_description:
        updates.append({"op": "replace", "path": "/description", "value": new_description})

    return update_metric(project_key, metric_key, updates)
```

## 5. Delete Metric (API)

```python
def delete_metric(project_key: str, metric_key: str):
    """Delete a metric from the project."""
    API_TOKEN = "{api_token}"  # token the user provided for this session

    url = f"https://app.launchdarkly.com/api/v2/metrics/{project_key}/{metric_key}"

    headers = {"Authorization": API_TOKEN}

    response = requests.delete(url, headers=headers)

    if response.status_code == 204:
        print(f"[OK] Deleted metric: {metric_key}")
        return True
    elif response.status_code == 404:
        print(f"[INFO] Metric not found: {metric_key}")
        return False
    else:
        print(f"[ERROR] Failed to delete metric: {response.status_code}")
        return False
```

## Complete Workflow Example

```python
import os
import requests
from ldclient import Context
from ldclient.config import Config
import ldclient

# Setup
API_TOKEN = "{api_token}"  # token the user provided for this session
SDK_KEY = os.environ.get("LAUNCHDARKLY_SDK_KEY")
PROJECT_KEY = "support-ai"

ldclient.set_config(Config(SDK_KEY))
ld_client = ldclient.get()

# 1. Create metric
create_metric(
    PROJECT_KEY,
    "ai.task.completion",
    name="Agent Task Completion Rate",
    kind="custom",
    is_numeric=True,
    description="Tracks successful agent task completions"
)

# 2. Track events
context = Context.builder("user-123").build()
ld_client.track("ai.task.completion", context, metric_value=1.0)
ld_client.track("ai.task.completion", context, metric_value=1.0)
ld_client.track("ai.task.completion", context, metric_value=0.0)  # failure
ld_client.flush()

# 3. Get metric definition
metric = get_metric(PROJECT_KEY, "ai.task.completion")

# 4. Update metric name
rename_metric(PROJECT_KEY, "ai.task.completion", "Agent Task Success Rate")

# 5. List all metrics
list_metrics(PROJECT_KEY)

# 6. Delete metric (when no longer needed)
# delete_metric(PROJECT_KEY, "ai.task.completion")
```

## Session Metrics Tracker

```python
import time
from ldclient import Context

class SessionMetricsTracker:
    """Track metrics across an entire user session."""

    def __init__(self, ld_client):
        self.ld_client = ld_client
        self.session_data = {}

    def start_session(self, user_id: str, session_id: str):
        """Initialize session tracking."""
        self.session_data[session_id] = {
            "user_id": user_id,
            "start_time": time.time(),
            "interactions": 0,
            "successful_tasks": 0
        }

    def track_interaction(self, session_id: str, success: bool):
        """Track individual interaction within session."""
        if session_id not in self.session_data:
            return
        session = self.session_data[session_id]
        session["interactions"] += 1
        if success:
            session["successful_tasks"] += 1

    def end_session(self, session_id: str):
        """Finalize and track session metrics."""
        if session_id not in self.session_data:
            return None

        session = self.session_data[session_id]
        duration = time.time() - session["start_time"]

        context = Context.builder(session["user_id"]).build()

        # Track session duration
        self.ld_client.track(
            "session.duration",
            context,
            data={"interactions": session["interactions"]},
            metric_value=duration
        )

        # Track session success rate
        if session["interactions"] > 0:
            success_rate = session["successful_tasks"] / session["interactions"]
            self.ld_client.track(
                "session.success_rate",
                context,
                metric_value=success_rate * 100
            )

        result = dict(session)
        result["duration"] = duration
        del self.session_data[session_id]
        return result
```

## Naming Conventions

```python
# Use dot notation for hierarchy
"quality.accuracy"
"quality.relevance"
"user.satisfaction"
"user.engagement"
"revenue.conversion"
"task.success_rate"
"session.duration"
"ai.task.completion"
"ai.recommendation.conversion"
```

## Best Practices

1. **Create Before Track** - Metric must exist before tracking events
2. **Use Numeric Metrics** - Set `isNumeric=True` for aggregation
3. **Consistent Keys** - Use same key in `create_metric()` and `ld_client.track()`
4. **Always flush before close** - Call `ld_client.flush()` (await in Node) before `close()`. Trailing events are at risk of being lost otherwise, in short-lived scripts and long-running services alike. This is not a serverless-only rule; it applies to any process that exits.
5. **Rate Limit** - Don't track on every keystroke

## Viewing Metrics

Custom metrics appear in:
- **Metrics** page in LaunchDarkly UI
- **Monitoring tab** of your config
- Via API using `get_metric()` or `list_metrics()`

## Related Skills

- `sdk` - SDK setup
- `built-in-metrics` - Built-in agent metrics (tokens, duration, cost)
- `online-evals` - Quality metrics via judges

## References

- [Metrics API Documentation](https://apidocs.launchdarkly.com/tag/Metrics)
- [Custom Events Documentation](https://docs.launchdarkly.com/sdk/features/events)
- [Python SDK track() Reference](https://launchdarkly-python-sdk.readthedocs.io/)