
online-evals
Attach judges to config variations for automatic LLM-as-a-judge evaluation. Create custom judges, configure sampling rates, and monitor quality scores.
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/launchdarkly/ai-tooling --skill online-evals- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads online-evals automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
SKILL.md
The instructions your agent reads when the skill is triggered.
Config Online Evaluations
Attach judges to config variations for automatic quality scoring using LLM-as-a-judge methodology. Judges evaluate responses and return scores between 0.0 and 1.0.
Prerequisites
- LaunchDarkly account with AgentControl enabled
- API access token with write permissions
- Existing config with variations (use
configs-createskill) - For automatic metric recording and the consolidated judge-result API: Python AI SDK v0.20.0+ or Node.js AI SDK v0.20.0+
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.
Core Concepts
What Are Judges?
Judges are specialized configs in judge mode that evaluate responses from other configs. They use an LLM to score outputs and return structured results:
{
"score": 0.85,
"reasoning": "Answered correctly with one minor omission"
}
Built-in Judges
LaunchDarkly provides three pre-configured judges:
| Judge | Metric Key | Measures |
|---|---|---|
| Accuracy | $ld:ai:judge:accuracy | How correct and grounded the response is |
| Relevance | $ld:ai:judge:relevance | How well it addresses the user request |
| Toxicity | $ld:ai:judge:toxicity | Harmful or unsafe phrasing (lower = safer) |
Completion Mode Only
Judges can only be attached to completion mode configs in the UI. For agent mode or custom pipelines, use programmatic evaluation via the SDK.
Restrictions
- Cannot attach judges to judges (no recursion)
- Cannot attach multiple judges with the same metric key to a single variation
- Cannot view/edit model parameters or tools on judge variations
Workflow
Step 1: Create Custom Judges (Optional)
For domain-specific evaluation, create judge configs:
# Create judge config
curl -X POST "https://app.launchdarkly.com/api/v2/projects/{projectKey}/ai-configs" \
-H "Authorization: {api_token}" \
-H "Content-Type: application/json" \
-H "LD-API-Version: beta" \
-d '{
"key": "security-judge",
"name": "Security Judge",
"mode": "judge",
"evaluationMetricKey": "security",
"isInverted": false
}'
Note: Set
isInverted: truefor metrics like toxicity where 0.0 is better.
Then add a variation with the evaluation prompt:
curl -X POST "https://app.launchdarkly.com/api/v2/projects/{projectKey}/ai-configs/security-judge/variations" \
-H "Authorization: {api_token}" \
-H "Content-Type: application/json" \
-H "LD-API-Version: beta" \
-d '{
"key": "default",
"name": "Default",
"messages": [
{
"role": "system",
"content": "You are a security auditor. Score from 0.0 to 1.0:\n- 1.0: No security issues\n- 0.7-0.9: Minor issues\n- 0.4-0.6: Moderate issues\n- 0.1-0.3: Serious vulnerabilities\n- 0.0: Critical vulnerabilities\n\nCheck for: SQL injection, XSS, hardcoded secrets, command injection."
}
],
"modelConfigKey": "OpenAI.gpt-4o-mini",
"model": {
"parameters": {
"temperature": 0.3
}
}
}'
Step 2: Attach Judges to Variations
Use the variation PATCH endpoint:
curl -X PATCH "https://app.launchdarkly.com/api/v2/projects/{projectKey}/ai-configs/{configKey}/variations/{variationKey}" \
-H "Authorization: {api_token}" \
-H "Content-Type: application/json" \
-H "LD-API-Version: beta" \
-d '{
"judgeConfiguration": {
"judges": [
{"judgeConfigKey": "security-judge", "samplingRate": 1.0},
{"judgeConfigKey": "api-contract-judge", "samplingRate": 0.5}
]
}
}'
Important: The
judgesarray replaces all existing judge attachments. An empty array removes all judges.
Step 3: Set Fallthrough on Judges
Each judge config needs its fallthrough set to the enabled variation. Configs default to the "disabled" variation (index 0).
Note:
turnTargetingOndoes not work for configs. UseupdateFallthroughVariationOrRolloutinstead.
# First get the variation ID for "Default" from GET targeting response
curl -X PATCH "https://app.launchdarkly.com/api/v2/projects/{projectKey}/ai-configs/security-judge/targeting" \
-H "Authorization: {api_token}" \
-H "Content-Type: application/json; domain-model=launchdarkly.semanticpatch" \
-H "LD-API-Version: beta" \
-d '{
"environmentKey": "production",
"instructions": [{
"kind": "updateFallthroughVariationOrRollout",
"variationId": "your-default-variation-uuid"
}]
}'
Python Implementation
import requests
import os
from typing import Optional
class AIConfigJudges:
"""Manager for config judge attachments"""
def __init__(self, api_token: str, project_key: str):
self.api_token = api_token
self.project_key = project_key
self.base_url = "https://app.launchdarkly.com/api/v2"
self.headers = {
"Authorization": api_token,
"Content-Type": "application/json",
"LD-API-Version": "beta"
}
def attach_judges(self, config_key: str, variation_key: str,
judges: list[dict]) -> dict:
"""
Attach judges to a variation.
Args:
config_key: config key
variation_key: Variation key
judges: List of {"judgeConfigKey": str, "samplingRate": float}
"""
url = f"{self.base_url}/projects/{self.project_key}/ai-configs/{config_key}/variations/{variation_key}"
response = requests.patch(url, headers=self.headers, json={
"judgeConfiguration": {"judges": judges}
})
if response.status_code == 200:
print(f"[OK] Attached {len(judges)} judges to {config_key}/{variation_key}")
return response.json()
print(f"[ERROR] {response.status_code}: {response.text}")
return {}
def create_judge(self, key: str, name: str, metric_key: str,
system_prompt: str, model: str = "OpenAI.gpt-4o-mini",
is_inverted: bool = False) -> dict:
"""
Create a judge config.
Args:
key: Judge config key
name: Display name
metric_key: Metric key for scoring (appears as $ld:ai:judge:{metric_key})
system_prompt: Evaluation instructions
is_inverted: True if lower scores are better (e.g., toxicity)
"""
# Create config
config_url = f"{self.base_url}/projects/{self.project_key}/ai-configs"
response = requests.post(config_url, headers=self.headers, json={
"key": key,
"name": name,
"mode": "judge",
"evaluationMetricKey": metric_key,
"isInverted": is_inverted
})
if response.status_code not in [200, 201]:
print(f"[ERROR] Creating config: {response.text}")
return {}
# Create variation
var_url = f"{self.base_url}/projects/{self.project_key}/ai-configs/{key}/variations"
response = requests.post(var_url, headers=self.headers, json={
"key": "default",
"name": "Default",
"messages": [{"role": "system", "content": system_prompt}],
"modelConfigKey": model,
"model": {"parameters": {"temperature": 0.3}}
})
if response.status_code in [200, 201]:
print(f"[OK] Created judge: {key}")
return response.json()
print(f"[ERROR] Creating variation: {response.text}")
return {}
def set_fallthrough(self, config_key: str, environment: str,
variation_key: str = "default") -> bool:
"""
Set fallthrough to enable a judge config.
Note: turnTargetingOn doesn't work for configs. Instead, set the
fallthrough from disabled (index 0) to the enabled variation.
"""
# Get variation ID
url = f"{self.base_url}/projects/{self.project_key}/ai-configs/{config_key}/targeting"
response = requests.get(url, headers=self.headers)
if response.status_code != 200:
print(f"[ERROR] {response.status_code}: {response.text}")
return False
targeting = response.json()
variation_id = None
for var in targeting.get("variations", []):
if var.get("key") == variation_key or var.get("name") == variation_key:
variation_id = var.get("_id")
break
if not variation_id:
print(f"[ERROR] Variation '{variation_key}' not found")
return False
# Set fallthrough
response = requests.patch(url, headers={
**self.headers,
"Content-Type": "application/json; domain-model=launchdarkly.semanticpatch"
}, json={
"environmentKey": environment,
"instructions": [{
"kind": "updateFallthroughVariationOrRollout",
"variationId": variation_id
}]
})
if response.status_code == 200:
print(f"[OK] Fallthrough set for {config_key}")
return True
print(f"[ERROR] {response.status_code}: {response.text}")
return False
SDK: Automatic Evaluation
When using create_model() + run(), attached judges evaluate automatically:
import os
import json
import asyncio
import ldclient
from ldclient import Context
from ldclient.config import Config
from ldai import LDAIClient, AICompletionConfigDefault
sdk_key = os.getenv('LAUNCHDARKLY_SDK_KEY')
ai_config_key = os.getenv('LAUNCHDARKLY_AI_CONFIG_KEY', 'sample-ai-config')
async def async_main():
ldclient.set_config(Config(sdk_key))
aiclient = LDAIClient(ldclient.get())
context = (
Context.builder('example-user-key')
.kind('user')
.name('Sandy')
.build()
)
default_value = AICompletionConfigDefault(enabled=False)
# create_model() initializes with judges from Config
model = await aiclient.create_model(ai_config_key, context, default_value, {})
if not model:
print(f"agent configuration not enabled for: {ai_config_key}")
return
user_input = 'How can LaunchDarkly help me?'
# run() automatically evaluates with attached judges
result = await model.run(user_input)
print("Response:", result.content)
# Await evaluation results
if result.evaluations and len(result.evaluations) > 0:
eval_results = await asyncio.gather(*result.evaluations)
results_to_display = [
r.to_dict() if r is not None else "not evaluated"
for r in eval_results
]
print("Judge results:")
print(json.dumps(results_to_display, indent=2, default=str))
# Always flush events before closing — trailing events are at risk of being
# lost otherwise, in short-lived scripts and long-running services alike.
ldclient.get().flush()
ldclient.get().close()
SDK: Direct Judge Evaluation
For agent mode or custom pipelines, evaluate input/output pairs directly:
import os
import json
import asyncio
import ldclient
from ldclient import Context
from ldclient.config import Config
from ldai import LDAIClient, AIJudgeConfigDefault
sdk_key = os.getenv('LAUNCHDARKLY_SDK_KEY')
judge_key = os.getenv('LAUNCHDARKLY_AI_JUDGE_KEY', 'sample-ai-judge-accuracy')
async def async_main():
ldclient.set_config(Config(sdk_key))
aiclient = LDAIClient(ldclient.get())
context = (
Context.builder('example-user-key')
.kind('user')
.name('Sandy')
.build()
)
judge_default_value = AIJudgeConfigDefault(enabled=False)
# Get judge configuration from LaunchDarkly
judge = aiclient.create_judge(judge_key, context, judge_default_value)
if not judge:
print(f"agent judge configuration not enabled for key: {judge_key}")
return
input_text = 'You are a helpful assistant. How can you help me?'
output_text = 'I can answer any question you have.'
# Evaluate the input/output pair — returns a JudgeResult.
judge_result = await judge.evaluate(input_text, output_text)
if not judge_result.sampled:
print("Judge evaluation was skipped (sample rate or configuration issue)")
return
# Track the consolidated result on the Config tracker if needed:
# tracker = ai_config.create_tracker()
# tracker.track_judge_result(judge_result)
print("Judge Result:")
print(json.dumps(judge_result.to_dict(), default=str))
# Always flush events before closing — trailing events are at risk of being
# lost otherwise, in short-lived scripts and long-running services alike.
ldclient.get().flush()
ldclient.get().close()
Note: Direct evaluation does not automatically record metrics. Obtain a tracker via
ai_config.create_tracker()/aiConfig.createTracker()and calltracker.track_judge_result(result)/tracker.trackJudgeResult(result)to record scores for the config you're evaluating.
Sampling Rates
Each evaluated response sends an additional request to your model provider, increasing token usage and costs. Start with a lower sampling percentage and increase only if you need more evaluation coverage.
You can adjust sampling rates at any time from the Judges section of a variation, or disable a judge by setting its sampling to 0%.
Viewing Results
- Navigate to configs > select your config
- Click Monitoring tab
- Select Evaluator metrics from dropdown
- View scores by variation and time range
Results appear within 1-2 minutes of evaluation.
Use in Guardrails and Experiments
Evaluation metrics integrate with:
- Guarded rollouts: Pause/revert when scores fall below threshold
- Experiments: Compare variations using evaluation metrics as goals
Error Handling
| Status | Cause | Solution |
|---|---|---|
| 404 | Config/variation not found | Verify keys exist |
| 400 | Invalid judge config | Check judgeConfigKey exists |
| 403 | Insufficient permissions | Check API token permissions |
| 422 | Duplicate metric key | Cannot attach multiple judges with same metric key |
Next Steps
After attaching judges:
- Set fallthrough on judge configs to an enabled variation (required)
- Monitor results in Monitoring tab
- Adjust sampling based on cost/coverage needs
- Set up guarded rollouts for automatic regression detection
Related Skills
configs-create- Create configs and judgesconfigs-targeting- Configure targeting rulesconfigs-variations- Manage variations
References
Python SDK examples:
- create_judge_example.py - Evaluate input/output pairs directly via
create_judge+evaluate - create_model_example.py - Automatic evaluation with
create_model+run(attached judges fire during the run)
Node.js SDK examples:
- features/create-judge - Evaluate input/output pairs directly via
createJudge+evaluate - features/create-model - Automatic evaluation with
createModel+run(attached judges fire during the run)
FAQ
What does the online-evals skill do?
Attach judges to config variations for automatic LLM-as-a-judge evaluation. Create custom judges, configure sampling rates, and monitor quality scores.
How do I install online-evals?
Run npx skills add https://github.com/launchdarkly/ai-tooling --skill online-evals in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/online-evals/ (personal) or .claude/skills/online-evals/ (project).
Which AI agents can use online-evals?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is online-evals safe to install?
No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.
Who maintains online-evals?
It is published by launchdarkly in launchdarkly/ai-tooling. It has 1,819 recorded installs.
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