Feature Flags Elixir — Agent Skill by PostHog

From the author

PostHog feature flags for Elixir applications

— the description by PostHog

AutoGineer summary

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

This skill provides guidance and best practices for implementing PostHog feature flags within Elixir applications. It covers the core principles of flag management, including the use of environment variables, server-side evaluation, and strategies for maintaining clean codebases. The skill also highlights how to leverage PostHog MCP tools to manage flags directly, reducing the need for manual dashboard interaction.

What it does

Provides patterns for integrating PostHog feature flags into Elixir code.
Outlines best practices for flag naming, targeting, and lifecycle management.
Recommends server-side evaluation to prevent UI flickering.
Supports the use of PostHog MCP tools for programmatic flag management.
Advises on using environment variables for secure configuration.

When to use it

When you need to perform controlled feature rollouts in an Elixir application.
When you want to manage feature flags programmatically via an AI agent.
When you need to implement A/B testing or canary releases.
When you want to ensure consistent flag behavior across user sessions.

Advantages

Promotes clean code by encouraging flag wrapping.
Improves performance through server-side and local evaluation strategies.
Enhances security by emphasizing environment variable usage.
Reduces manual overhead by integrating with MCP-enabled tools.

Usage examples

“How do I implement a boolean feature flag in my Elixir service?”: The agent provides a code pattern for checking the flag status server-side, ensuring the logic is encapsulated and uses environment variables for the PostHog key.
“Can you help me create a new feature flag for my beta users?”: The agent uses the connected PostHog MCP tools to create the flag directly in your project, following the recommended naming conventions.

Install

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

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

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

Documentation by PostHog

PostHog feature flags for Elixir

This skill helps you add PostHog feature flags to Elixir applications.

Reference files

references/elixir.md - Elixir feature flags installation - docs
references/adding-feature-flag-code.md - Adding feature flag code - docs
references/best-practices.md - Feature flag best practices - docs

Consult the documentation for API details and framework-specific patterns.

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.

PostHog MCP tools

Check if a PostHog MCP server is connected. If available, look for tools related to feature flag management (creating, listing, updating, deleting flags). Use these tools to manage flags directly in PostHog rather than requiring the user to do it manually in the dashboard.

Framework guidelines

No specific framework guidelines.

Files

ATTRIBUTION.mdAdded by AutoGineer960 B
LICENSELicence file added by AutoGineer1.0 KiB
SKILL.md1.3 KiB
references/adding-feature-flag-code.md108.7 KiB
references/best-practices.md7.9 KiB
references/elixir.md1.3 KiB

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

Security

No issues found by our static scan· No issues found

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

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