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posthog-core-workflow-b Implement PostHog feature flags, A/B experiments, and cohort management.
Use when rolling out features with flags, running A/B tests, creating cohorts,
or evaluating multivariate experiments with PostHog.
Trigger: "posthog feature flag", "posthog experiment", "posthog A/B test",
"posthog cohort", "feature rollout posthog", "posthog multivariate".
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name posthog-core-workflow-b description Implement PostHog feature flags, A/B experiments, and cohort management.
Use when rolling out features with flags, running A/B tests, creating cohorts,
or evaluating multivariate experiments with PostHog.
Trigger: "posthog feature flag", "posthog experiment", "posthog A/B test",
"posthog cohort", "feature rollout posthog", "posthog multivariate".
allowed-tools Read, Write, Edit, Bash(npm:*), Grep version 1.12.0 license MIT author Jeremy Longshore <jeremy@intentsolutions.io> tags ["saas","posthog","workflow","feature-flags","experiments"] compatibility Designed for Claude Code
PostHog Core Workflow B — Feature Flags & Experiments
Overview
Feature flag management, A/B experiment evaluation, and cohort analysis with PostHog. Covers boolean and multivariate flags, local evaluation for performance, experiment setup and statistical significance, and cohort creation via the API.
Prerequisites
Completed posthog-install-auth setup
Familiarity with posthog-core-workflow-a (event capture)
Personal API key (phx_...) for flag management API
Instructions
Step 1: Evaluate Feature Flags (Browser)
import posthog from 'posthog-js' ;
if (posthog.isFeatureEnabled ('new-checkout-flow' )) {
renderNewCheckout ();
} else {
renderLegacyCheckout ();
}
const variant = posthog.getFeatureFlag ('pricing-page-experiment' );
switch (variant) {
case 'control' :
renderOriginalPricing ();
break ;
case 'annual-first' :
renderAnnualFirstPricing ();
break ;
case 'social-proof' :
renderSocialProofPricing ();
break ;
default :
renderOriginalPricing ();
}
const payload = posthog.getFeatureFlagPayload ('banner-config'
onFeatureFlags
() =>
const
isFeatureEnabled
'new-feature'
setFeatureEnabled
false
Step 2: Evaluate Feature Flags (Server — posthog-node) import { PostHog } from 'posthog-node' ;
const posthog = new PostHog (process.env .NEXT_PUBLIC_POSTHOG_KEY !, {
host : 'https://us.i.posthog.com' ,
personalApiKey : process.env .POSTHOG_PERSONAL_API_KEY ,
});
async function checkFlag (userId : string Promise <boolean > {
const enabled = await posthog.isFeatureEnabled ('new-api-version' , userId);
return enabled ?? false ;
}
async function getVariant (userId : string Promise <string > {
const variant = await posthog.getFeatureFlag ('onboarding-experiment' , userId, {
personProperties : { plan : 'pro' , country : 'US' },
});
return (variant as string ) || 'control' ;
}
async function getUserFlags (userId : string const flags = await posthog.getAllFlags (userId, {
personProperties : { plan : 'enterprise' },
groupProperties : { company : { name : 'Acme' } },
});
return flags;
}
async function getFlagsAndPayloads (userId : string const result = await posthog.getAllFlagsAndPayloads (userId);
return result;
}
Step 3: Create Feature Flags via API set -euo pipefail
curl -X POST "https://app.posthog.com/api/projects/$POSTHOG_PROJECT_ID /feature_flags/" \
-H "Authorization: Bearer $POSTHOG_PERSONAL_API_KEY " \
-H "Content-Type: application/json" \
-d '{
"key": "new-dashboard-v2",
"name": "New Dashboard V2",
"active": true,
"filters": {
"groups": [{
"rollout_percentage": 25,
"properties": []
}]
}
}'
curl -X POST "https://app.posthog.com/api/projects/$POSTHOG_PROJECT_ID /feature_flags/" \
-H "Authorization: Bearer $POSTHOG_PERSONAL_API_KEY " \
-H "Content-Type: application/json" \
-d '{
"key": "checkout-experiment",
"name": "Checkout Flow Experiment",
"active": true,
"filters": {
"multivariate": {
"variants": [
{"key": "control", "rollout_percentage": 50},
{"key": "streamlined", "rollout_percentage": 50}
]
},
"groups": [{"rollout_percentage": 100, "properties": []}]
}
}'
Step 4: Set Up an Experiment
async function runExperiment (userId : string const posthog = new PostHog (process.env .NEXT_PUBLIC_POSTHOG_KEY !);
const variant = await posthog.getFeatureFlag ('checkout-experiment' , userId);
posthog.capture ({
distinctId : userId,
event : 'purchase_completed' ,
properties : {
variant,
order_value : 49.99 ,
},
});
await posthog.flush ();
return variant;
}
Step 5: Query Experiment Results via API set -euo pipefail
curl "https://app.posthog.com/api/projects/$POSTHOG_PROJECT_ID /experiments/" \
-H "Authorization: Bearer $POSTHOG_PERSONAL_API_KEY " | \
jq '.results[] | {id, name, start_date, end_date, feature_flag_key}'
curl "https://app.posthog.com/api/projects/$POSTHOG_PROJECT_ID /experiments/EXPERIMENT_ID/results/" \
-H "Authorization: Bearer $POSTHOG_PERSONAL_API_KEY " | \
jq '{
variants: [.result.variants[] | {key, count, conversion_rate: .absolute_exposure}],
significance: .result.significance_code,
probability: .result.probability
}'
Step 6: Manage Cohorts via API set -euo pipefail
curl -X POST "https://app.posthog.com/api/projects/$POSTHOG_PROJECT_ID /cohorts/" \
-H "Authorization: Bearer $POSTHOG_PERSONAL_API_KEY " \
-H "Content-Type: application/json" \
-d '{
"name": "Recent Signups (30d)",
"is_calculating": true,
"filters": {
"properties": {
"type": "AND",
"values": [{
"type": "AND",
"values": [{
"key": "user_signed_up",
"type": "behavioral",
"value": "performed_event",
"time_value": 30,
"time_interval": "day"
}]
}]
}
}
}'
curl "https://app.posthog.com/api/projects/$POSTHOG_PROJECT_ID /cohorts/" \
-H "Authorization: Bearer $POSTHOG_PERSONAL_API_KEY " | \
jq '.results[] | {id, name, count, is_calculating}'
Error Handling Error Cause Solution Flag always returns undefined Flags not loaded yet Use posthog.onFeatureFlags() callback Flag returns default on server No personalApiKey set Add personal API key for local evaluation Experiment not tracking Goal event name mismatch Verify event name matches experiment config Cohort stuck is_calculating Large dataset Wait for calculation; check PostHog status getAllFlags slowNo local evaluation Set personalApiKey in PostHog constructor
Output
Feature flag evaluation (boolean and multivariate)
Server-side local evaluation for low-latency flag checks
A/B experiment setup with goal metric tracking
Cohort creation and management via API
Experiment results with statistical significance
Resources
Next Steps For common errors, see posthog-common-errors.
