security

A set of security, error-handling, and debugging rules for the Keymoji application. The rules cover user-input validation, browser attack prevention, API protection, secure storage, and consistent failure handling.

In plain words
What is it for?
Use it when writing or reviewing Keymoji code that handles user input, API calls, OTP or magic-link login, stored data, critical components, localized errors, or development-only logging.
Why use it?
It gives development work a shared checklist for reducing common security and reliability problems. It also requires async failures to be caught, explained to users, and given fallback values.

Cursor rule for Cursor

Install

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.

agentmods
npx agentmods add rules/chooomedia/keymoji/security
Clone the repo
git clone --depth 1 https://github.com/chooomedia/keymoji

Made for: Cursor.

Per session 11 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 376 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00011 $0.00376
Opus 5 $0.00005 $0.00188
Sonnet 5 $0.00002 $0.00075
Haiku 4.5 $0.00001 $0.00038

Measured yesterday against content hash 494b100a6f42, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

security 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 yesterday.

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.

.cursor/rules/security.mdc · 55 lines

What it actually says

Security & Error Handling

Sicherheit

  • Input Validation für alle User-Eingaben
  • XSS Prevention — keine direkte DOM-Manipulation mit User-Daten
  • CSRF Protection via X-Requested-With Header
  • Rate Limiting für alle API Calls
  • Secure Storage — keine sensitiven Daten im Klartext in localStorage
  • OTP/Magic-Link: Single-Use Tokens, Token Expiry prüfen, Rate Limiting

Error Handling (Pflicht-Pattern)

try {
  const result = await apiCall();
  return result;
} catch (error) {
  console.error('API Error:', error);
  showError('Failed to load data. Please try again.');
  return defaultValue;
}
  • IMMER try/catch für async Operations
  • IMMER user-freundliche Error Messages (lokalisiert via $translations)
  • IMMER Fallback Values
  • Error Boundaries für kritische Komponenten

Debugging

  • isDevelopment() aus utils/environment.js für Debug-Code
  • Console Logs nur in Development — nie in Production-Pfaden
  • Console Logs mit Emojis für Kategorisierung:
    • Erfolg, Fehler, ⚠️ Warning, 📊 Data, 🔄 Sync, 📡 API

JSDoc für Funktionen

/**
 * Loads account data from backend
 * @param userId - The user ID
 * @param options - Optional parameters
 * @returns Promise with account data
 */
async function loadAccount(userId: string, options?: LoadOptions): Promise<Account> {
  // ...
}
Changes

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.

  1. yesterday First seen · 55 lines · 11 tokens per session scan A 494b100a6f42

Subscribe to this mod's changes

security is a cursor rule published in the GitHub repository chooomedia/keymoji (2 stars, last pushed 1mo ago), licensed MIT. It adds 11 tokens to every session and 376 once invoked, about $0.0001 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 2026-08-31.