Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add aj-geddes/useful-ai-prompts --skill feature-flag-systemgit clone --depth 1 https://github.com/aj-geddes/useful-ai-promptsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/aj-geddes/useful-ai-prompts/feature-flag-system)<a href="https://agentmods.dev/skills/aj-geddes/useful-ai-prompts/feature-flag-system"><img src="https://agentmods.dev/badge/skills/aj-geddes/useful-ai-prompts/feature-flag-system/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/aj-geddes/useful-ai-prompts/feature-flag-system"><img src="https://agentmods.dev/badge/skills/aj-geddes/useful-ai-prompts/feature-flag-system.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- Socket pass
- Snyk pass
What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00048 | $0.00634 |
| Opus 5 | $0.00024 | $0.00317 |
| Sonnet 5 | $0.00010 | $0.00127 |
| Haiku 4.5 | $0.00005 | $0.00063 |
Grade A, and why
feature-flag-system scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 9d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 103 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Feature Flag System
Table of Contents
Overview
Implement feature flags to decouple deployment from release, enable gradual rollouts, A/B testing, and provide emergency kill switches.
When to Use
- Gradual feature rollouts
- A/B testing and experiments
- Canary deployments
- Beta features for specific users
- Emergency kill switches
- Trunk-based development
- Dark launching
- Operational flags (maintenance mode)
- User-specific features
Quick Start
Minimal working example:
interface FlagConfig {
key: string;
enabled: boolean;
description: string;
rules?: FlagRule[];
variants?: FlagVariant[];
createdAt: Date;
updatedAt: Date;
}
interface FlagRule {
type: "user" | "percentage" | "attribute" | "datetime";
operator: "in" | "equals" | "contains" | "gt" | "lt" | "between";
attribute?: string;
values: any[];
}
interface FlagVariant {
key: string;
weight: number;
value: any;
}
interface EvaluationContext {
userId?: string;
// ... (see reference guides for full implementation)
Reference Guides
Detailed implementations in the references/ directory:
| Guide | Contents |
|---|---|
| Feature Flag Service (TypeScript) | Feature Flag Service (TypeScript) |
| React Hook for Feature Flags | React Hook for Feature Flags |
| Feature Flag with Analytics | Feature Flag with Analytics |
| LaunchDarkly-Style SDK | LaunchDarkly-Style SDK |
| Admin UI for Feature Flags | Admin UI for Feature Flags |
Best Practices
✅ DO
- Use descriptive flag names
- Document flag purpose and lifecycle
- Implement gradual rollouts
- Track flag evaluations
- Clean up old flags regularly
- Use feature flags for experiments
- Implement kill switches for critical features
- Test both enabled and disabled states
- Use consistent hashing for stable rollouts
- Provide admin UI for non-technical users
What ships with it
7 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
- references/admin-ui-for-feature-flags.md 1.7 KB
- references/feature-flag-service-typescript.md 6.3 KB
- references/feature-flag-with-analytics.md 1.7 KB
- references/launchdarkly-style-sdk.md 3.8 KB
- references/react-hook-for-feature-flags.md 2.1 KB
- scripts/scaffold-tests.sh 574 B runs code
- templates/test-template.js 541 B runs code
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 9d ago First seen · 103 lines · 48 tokens per session scan A bf56a8631fd4
feature-flag-system is a skill published in the GitHub repository aj-geddes/useful-ai-prompts (338 stars, last pushed 6mo ago), licensed MIT. It adds 48 tokens to every session and 634 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.
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