Feature Flags Web — Agent Skill by PostHog

From the author

PostHog feature flags for Web (JavaScript) 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 code patterns for implementing PostHog feature flags within JavaScript web applications. It covers installation, flag evaluation, handling asynchronous loading, and best practices for maintaining clean, performant code. The skill emphasizes strategies to minimize UI flicker, ensure consistent user experiences through proper identification, and improve performance via local evaluation and bootstrapping.

What it does

Provides code snippets for implementing boolean and multivariate feature flags.
Explains how to handle asynchronous flag loading using callbacks.
Offers techniques for bootstrapping flags to ensure immediate availability.
Details methods for reloading flags and overriding server-side properties.
Outlines best practices for flag naming, targeting, and architectural organization.
Supports management of flags via PostHog MCP tools if connected.

When to use it

When you need to perform feature rollouts or A/B testing in a web application.
When you want to decouple feature deployment from code deployment.
When you need to ensure consistent user experiences across sessions and devices.
When you are looking to optimize flag performance and reduce network latency in your app.

Advantages

Reduces the risk of deploying new features by allowing instant toggling.
Improves application performance through local evaluation and bootstrapping.
Provides clear patterns for maintaining clean code when using flags.
Helps prevent UI flicker by leveraging server-side evaluation or bootstrapping.

Usage examples

“How do I check if a boolean feature flag is enabled in my JavaScript app?”: The agent provides the posthog.isFeatureEnabled('flag-key') code snippet and explains how to use it within your application logic.
“How can I ensure my feature flags are ready before my page renders?”: The agent explains the use of the posthog.onFeatureFlags callback to wait for flag definitions to load before executing dependent code.

Install

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

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

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

Documentation by PostHog

PostHog feature flags for Web (JavaScript)

This skill helps you add PostHog feature flags to Web (JavaScript) applications.

Reference files

references/web.md - Web 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 AutoGineer951 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/web.md6.8 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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