Omnibus Instrument Feature Flags

PostHogOfficialCreated by PostHog

Skill
Tool integration
Data and AI
MIT
Low risk

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

Download the skill as a ZIP:
https://autogineer.com/agent-skills/posthog/omnibus-instrument-feature-flags/download

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

ATTRIBUTION.mdAdded by AutoGineer966 B
LICENSELicence file added by AutoGineer1.0 KiB
SKILL.md4.7 KiB
references/adding-feature-flag-code.md108.7 KiB
references/android.md3.5 KiB
references/api.md5.6 KiB
references/best-practices.md7.9 KiB
references/dotnet.md6.8 KiB
references/elixir.md1.3 KiB
references/flutter.md5.9 KiB
references/go.md5.3 KiB
references/ios.md3.5 KiB
references/java.md2.3 KiB
references/next-js.md12.5 KiB
references/nodejs.md5.3 KiB
references/php.md4.6 KiB
references/python.md5.0 KiB
references/react-native.md4.3 KiB
references/react.md8.1 KiB
references/ruby.md4.9 KiB
references/rust.md4.3 KiB
references/web.md6.8 KiB

references/dotnet.md

.NET feature flags installation - Docs

The PostHog package supports any .NET platform that targets .NET Standard 2.1 or .NET 8+, including MAUI, Blazor, and console applications. The PostHog.AspNetCore package provides additional conveniences for ASP.NET Core applications such as streamlined registration, request-scoped caching, and integration with .NET Feature Management.

Note: We actively test with ASP.NET Core. Other platforms should work but haven't been specifically tested. If you encounter issues, please report them on GitHub.

Not supported: Classic UWP (requires .NET Standard 2.0 only). Microsoft has deprecated UWP in favor of the Windows App SDK. For Unity projects, see our dedicated Unity SDK (currently in beta).

Terminal

PostHog AI

dotnet add package PostHog.AspNetCore

In your Program.cs (or Startup.cs for ASP.NET Core 2.x) file, add the following code:

PostHog AI

using PostHog;
var builder = WebApplication.CreateBuilder(args);
// Add PostHog to the dependency injection container as a singleton.
builder.AddPostHog();

Make sure to configure PostHog with your project token, instance address, and optional personal API key. For example, in appsettings.json:

JSON

PostHog AI

{
  "PostHog": {
    "ProjectApiKey": "<ph_project_token>",
    "HostUrl": "https://us.i.posthog.com"
  }
}

Note: If the host is not specified, the default host https://us.i.posthog.com is used.

Use a secrets manager to store your personal API key. For example, when developing locally you can use the UserSecrets feature of the dotnet CLI:

Terminal

PostHog AI

dotnet user-secrets init
dotnet user-secrets set "PostHog:PersonalApiKey" "phx_..."

You can find your project token and instance address in the project settings page in PostHog.

Working with .NET Feature Management

PostHog.AspNetCore supports .NET Feature Management. This enables you to use the <feature /> tag helper and the FeatureGateAttribute in your ASP.NET Core applications to gate access to certain features using PostHog feature flags.

To use feature flags with the .NET Feature Management library, you'll need to implement the IPostHogFeatureFlagContextProvider interface. The quickest way to do that is to inherit from the PostHogFeatureFlagContextProvider class and override the GetDistinctId and GetFeatureFlagOptionsAsync methods.

PostHog AI

public class MyFeatureFlagContextProvider(IHttpContextAccessor httpContextAccessor)
    : PostHogFeatureFlagContextProvider
{
    protected override string? GetDistinctId()
        => httpContextAccessor.HttpContext?.User.Identity?.Name;
    protected override ValueTask<FeatureFlagOptions> GetFeatureFlagOptionsAsync()
    {
        // In a real app, you might get this information from a
        // database or other source for the current user.
        return ValueTask.FromResult(
            new FeatureFlagOptions
            {
                PersonProperties = new Dictionary<string, object?>
                {
                    ["email"] = "[email protected]"
                },
                OnlyEvaluateLocally = true
            });
    }
}

Then, register your implementation in Program.cs (or Startup.cs):

PostHog AI

var builder = WebApplication.CreateBuilder(args);
builder.AddPostHog(options => {
    options.UseFeatureManagement<MyFeatureFlagContextProvider>();
});

With this in place, you can now use feature tag helpers in your Razor views:

HTML

PostHog AI

<feature name="awesome-new-feature">
    <p>This is the new feature!</p>
</feature>
<feature name="awesome-new-feature" negate="true">
    <p>Sorry, no awesome new feature for you.</p>
</feature>

Multivariate feature flags are also supported:

HTML

PostHog AI

<feature name="awesome-new-feature" value="variant-a">
    <p>This is the new feature variant A!</p>
</feature>
<feature name="awesome-new-feature" value="variant-b">
    <p>This is the new feature variant B!</p>
</feature>

You can also use the FeatureGateAttribute to gate access to controllers or actions:

PostHog AI

[FeatureGate("awesome-new-feature")]
public class NewFeatureController : Controller
{
    public IActionResult Index()
    {
        return View();
    }
}

Using the core package without ASP.NET Core

If you're not using ASP.NET Core (for example, in a console application, MAUI app, or Blazor WebAssembly), install the PostHog package instead of PostHog.AspNetCore. This package has no ASP.NET Core dependencies and can be used in any .NET project targeting .NET Standard 2.1 or .NET 8+.

Terminal

PostHog AI

dotnet add package PostHog

The PostHogClient class must be implemented as a singleton in your project. For PostHog.AspNetCore, this is handled by the builder.AddPostHog(); method. For the PostHog package, you can do the following if you're using dependency injection:

PostHog AI

builder.Services.AddPostHog();

If you're not using a builder (such as in a console application), you can do the following:

PostHog AI

using PostHog;
var services = new ServiceCollection();
services.AddPostHog();
var serviceProvider = services.BuildServiceProvider();
var posthog = serviceProvider.GetRequiredService<IPostHogClient>();

The AddPostHog methods accept an optional Action<PostHogOptions> parameter that you can use to configure the client.

If you're not using dependency injection, you can create a static instance of the PostHogClient class and use that everywhere in your project:

PostHog AI

using PostHog;
public static readonly PostHogClient PostHog = new(new PostHogOptions {
    ProjectApiKey = "<ph_project_token>",
    HostUrl = new Uri("https://us.i.posthog.com"),
    PersonalApiKey = Environment.GetEnvironmentVariable(
      "PostHog__PersonalApiKey")
});

Debug mode

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

To see detailed logging, set the log level to Debug or Trace in appsettings.json:

JSON

PostHog AI

{
  "DetailedErrors": true,
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning",
      "PostHog": "Trace"
    }
  },
  ...
}

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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

2026-11-09

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

From the author

AutoGineer summary

What it does

When to use it

Advantages

Usage examples

Install

Documentation by PostHog

Add PostHog feature flags

Instructions

Reference files

Key principles

Files

references/dotnet.md

.NET feature flags installation - Docs

Working with .NET Feature Management

Using the core package without ASP.NET Core

Debug mode

Community questions

Was this page useful?

Requirements and compatibility

Security

Attribution and licence

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