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Omnibus Instrument Feature Flags

PostHogOfficialCreated by PostHog

  • Skill
  • Tool integration
  • Data and AI
  • MIT
  • Low risk
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From the author

Add PostHog feature flags to gate new functionality. Use after implementing features or reviewing PRs to ensure safe rollouts with feature flag controls. Also handles initial PostHog SDK setup if not yet installed.
— the description by PostHog

AutoGineer summary

Written by AutoGineer from the skill’s own files, not by the author

This skill provides a structured approach to instrumenting PostHog feature flags across a wide range of platforms and languages. It guides the user through detecting their current environment, setting up the PostHog SDK if necessary, and implementing the logic required to gate new functionality. By following these steps, developers can manage phased rollouts, target specific user groups, and perform multivariate testing without hardcoding sensitive configuration values.

What it does

  • Detects the project platform and framework to provide relevant SDK setup instructions.
  • Automates or guides the initialization of the PostHog SDK.
  • Provides standardized code patterns for evaluating boolean and multivariate feature flags.
  • Ensures secure configuration by enforcing the use of environment variables for API keys.
  • Supports a broad range of languages including Python, JavaScript, Go, Java, and mobile frameworks.
  • Offers guidance on best practices for feature flag implementation and lifecycle management.

When to use it

  • When you need to gate new features to perform a phased or canary rollout.
  • When you want to run A/B tests or experiments on specific user segments.
  • When you need to implement a kill-switch for new functionality in production.
  • When setting up PostHog for the first time in a new or existing codebase.

Advantages

  • Promotes safe deployment practices by decoupling code deployment from feature release.
  • Reduces risk by allowing immediate feature toggling without requiring a new deployment.
  • Supports consistent implementation patterns across diverse tech stacks.
  • Encourages secure development by prioritizing environment variables over hardcoded secrets.

Usage examples

“I want to gate my new checkout button with a PostHog feature flag in my React app.”
The agent will analyze your React project, verify the PostHog SDK installation, and provide the specific code snippet to wrap your component logic with a feature flag check.
“How do I set up PostHog feature flags in my Android project?”
The agent will guide you through adding the dependency to your build.gradle, initializing the SDK in your Application class, and implementing the flag evaluation logic.

Install

  1. Download the skill as a ZIP:

    https://autogineer.com/agent-skills/posthog/omnibus-instrument-feature-flags/download

  2. Unzip it into the cross-client skills folder of your project:

    mkdir -p .agents/skills && unzip omnibus-instrument-feature-flags.zip -d .agents/skills

Documentation by PostHog

Add PostHog feature flags

Use this skill to add PostHog feature flags that gate new or changed functionality. Use it after implementing features or reviewing PRs to ensure safe rollouts with feature flag controls. If PostHog is not yet installed, this skill also covers initial SDK setup. Supports any platform or language.

Supported platforms: React, Next.js, React Native, Web (JavaScript), Node.js, Python, PHP, Ruby, Go, Java, Rust, .NET, Elixir, Android, iOS, Flutter, and the REST API.

Instructions

Follow these steps IN ORDER:

STEP 1: Analyze the codebase and detect the platform.

  • Look for dependency files (package.json, requirements.txt, go.mod, Gemfile, composer.json, etc.) to determine the language and framework.

  • Look for lockfiles (pnpm-lock.yaml, package-lock.json, yarn.lock, bun.lockb) to determine the package manager.

  • Check for existing PostHog setup (SDK initialization, env vars, etc.). If PostHog is already installed and initialized, skip to STEP 3.

STEP 2: Research instrumentation. (Skip if PostHog is already set up.) 2.1. Find the reference file below that matches the detected platform — it is the source of truth for SDK initialization, flag evaluation methods, and framework-specific patterns. Read it now. 2.2. If no reference matches, fall back to your general knowledge and web search. Use posthog.com/docs as the primary search source.

STEP 3: Create or find the feature flag.

  • Check if a PostHog MCP server is connected. If available, use its tools to search for an existing feature flag the user wants to instrument, or create a new one.

  • If no MCP server is available, instruct the user to create the flag in the PostHog dashboard.

STEP 4: Plan release conditions.

  • Determine the rollout strategy (percentage rollout, user targeting, group targeting, etc.).

  • Plan how the feature flag will gate the new functionality in code.

STEP 5: Instrument the feature.

  • Add the feature flag code following the platform-specific reference patterns.

  • Use server-side evaluation when possible to avoid UI flicker.

  • Do not alter the fundamental architecture of existing files. Make additions minimal and targeted.

  • You must read a file immediately before attempting to write it.

STEP 6: Set up environment variables.

  • If an env-file-tools MCP server is connected, use check_env_keys to see which keys already exist, then use set_env_values to create or update the PostHog API key and host.

  • Reference these environment variables in code instead of hardcoding them.

Reference files

  • references/react.md - React feature flags installation - docs

  • references/react-native.md - React native feature flags installation - docs

  • references/web.md - Web feature flags installation - docs

  • references/nodejs.md - Node.js feature flags installation - docs

  • references/python.md - Python feature flags installation - docs

  • references/php.md - Php feature flags installation - docs

  • references/ruby.md - Ruby feature flags installation - docs

  • references/go.md - Go feature flags installation - docs

  • references/java.md - Java feature flags installation - docs

  • references/rust.md - Rust feature flags installation - docs

  • references/dotnet.md - .net feature flags installation - docs

  • references/elixir.md - Elixir feature flags installation - docs

  • references/android.md - Android feature flags installation - docs

  • references/ios.md - Ios feature flags installation - docs

  • references/flutter.md - Flutter feature flags installation - docs

  • references/api.md - API feature flags installation - docs

  • references/next-js.md - Next.js - docs

  • references/adding-feature-flag-code.md - Adding feature flag code - docs

  • references/best-practices.md - Feature flag best practices - docs

Each platform reference contains SDK-specific installation, flag evaluation, and code examples. Find the one matching the user's stack. If unlisted, use the API reference as a fallback.

Key principles

  • Environment variables: Always use environment variables for PostHog keys. Never hardcode them.

  • Minimal changes: Add feature flag code alongside existing logic. Don't replace or restructure existing code.

  • Boolean flags first: Default to boolean flag checks unless the user specifically asks for multivariate flags.

  • Server-side when possible: Prefer server-side flag evaluation to avoid UI flicker.

Files

references/java.md

Java feature flags installation - Docs

The best way to install the PostHog Java SDK is with a build system like Gradle or Maven. This ensures you can easily upgrade to the latest versions.

Look up the latest version of com.posthog.posthog-server.

Gradle

All you need to do is add the posthog-server module to your build.gradle:

build.gradle

PostHog AI

dependencies {
  implementation 'com.posthog:posthog-server:2.+'
}
Maven

All you need to do is add the posthog-server module to your pom.xml:

pom.xml

PostHog AI

<dependency>
  <groupId>com.posthog</groupId>
  <artifactId>posthog-server</artifactId>
  <version>LATEST</version>
</dependency>
Other

See com.posthog.posthog-server in the Maven Central Repository. Clicking on the latest version shows you options for adding dependencies for other build systems.

Setup

Java

PostHog AI

import com.posthog.server.PostHog;
import com.posthog.server.PostHogConfig;
import com.posthog.server.PostHogInterface;
class Sample {
  private static final String POSTHOG_API_KEY = "<ph_project_token>";
  private static final String POSTHOG_HOST = "https://us.i.posthog.com";
  public static void main(String args[]) {
    PostHogConfig config = PostHogConfig
            .builder(POSTHOG_API_KEY)
            .host(POSTHOG_HOST)
            .build();
    PostHogInterface posthog = PostHog.with(config);
    posthog.flush(); // send any remaining events
    posthog.close(); // shut down the client
  }
}

Integrating with Spring

To see how to integrate the PostHog SDK with Spring, check out this sample project.

Debug mode

If you're not seeing the expected events being captured, or the feature flags being evaluated, you can enable debug mode to see what's happening.

To see detailed logging, set the debug configuration option to true.

Java

PostHog AI

PostHogConfig config = PostHogConfig
          .builder(POSTHOG_API_KEY)
          .host(POSTHOG_HOST)
          .debug(true)
          .build();
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Requirements and compatibility

Works with: Claude Code, Claude apps, OpenAI Codex, GitHub Copilot, Cursor, Gemini CLI, Kiro, OpenCode, Goose, Amp, Roo Code, JetBrains Junie, Factory Droid, Devin (ex-Windsurf), Mistral Vibe, OpenHands, Letta

“Works with” means the tool reads the open Agent Skills format; a skill written for one tool may use features others lack.

Needs: Needs an MCP server, Needs an API key, Needs Python, Needs Node.js

Security

What our scanner noticed· Low risk

  • Instructions that use the network

A static scan is not a guarantee. Skills are third-party content: review a skill before you let an agent use it.

Attribution and licence

Created by
PostHog
Publisher
PostHog (Official)
Source
PostHog/skills · skills/posthog/feature-flags/skills/all · commit a5d30e7
Licence
MIT License (redistribution allowed)
  • LICENSE (added by AutoGineer from LICENSE)
  • ATTRIBUTION.md (written by AutoGineer)
Synced
Also distributed in
PostHog/skills

AutoGineer is not affiliated with or endorsed by PostHog or PostHog.

Download ZIP

The ZIP holds the skill’s files, its licence files and an ATTRIBUTION.md. Download omnibus-instrument-feature-flags.zip