Feature Flags Nodejs — Agent Skill by PostHog

From the author

PostHog feature flags for Node.js 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 Node.js environments. It covers installation, code implementation patterns, and architectural strategies to ensure efficient and reliable feature management. The skill emphasizes server-side evaluation, the use of environment variables for security, and maintaining clean code by centralizing flag logic.

What it does

Provides patterns for implementing boolean and multivariate feature flags in Node.js.
Outlines best practices for flag naming and organization to improve maintainability.
Advises on using server-side evaluation to prevent UI flickering.
Recommends strategies like reverse proxies to ensure flag reliability against ad blockers.
Suggests wrapping flag checks in helper functions to minimize code duplication.
Integrates with PostHog MCP tools for direct flag management via the agent.

When to use it

When you need to perform controlled feature rollouts or experiments in a Node.js backend.
When you want to manage feature flags programmatically rather than manually in the dashboard.
When you need to ensure consistent user experiences across sessions by identifying users or groups.
When you are looking to optimize flag evaluation performance using local evaluation techniques.

Advantages

Reduces code clutter by encouraging centralized flag logic.
Improves performance by supporting local flag evaluation.
Enhances security by enforcing the use of environment variables for API keys.
Increases reliability by providing strategies to bypass ad-blocking interference.

Usage examples

“How do I check a boolean feature flag in my Node.js service?”: The agent will provide a code snippet using the appropriate PostHog method to evaluate the flag and explain how to wrap it in a function for cleaner code.
“Can you help me create a new feature flag for my beta users?”: The agent will check for a connected PostHog MCP server and use the available tools to create the flag directly in your PostHog project.

Install

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

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

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

Documentation by PostHog

PostHog feature flags for Node.js

This skill helps you add PostHog feature flags to Node.js applications.

Reference files

references/nodejs.md - Node.js 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/nodejs.md5.3 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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