# caching

Use this skill to plan or review caching, from TTL choices and cache keys to invalidation. It fits work on API, service, and client-side caches.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · ★ 4679
- Author: zebbern
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/zebbern/claude-code-guide/tree/HEAD/skills/caching/SKILL.md
- Updated: 2026-10-24
- HTML: https://affpapa.org/en/nevibecode/skills/zebbern-caching

## What it does

The skill helps choose between in-memory storage, Redis, CDN, and HTTP cache headers, then match TTLs to how quickly the underlying data changes. It covers cache keys that account for query parameters and namespaces that reduce collisions between services.

Every cache needs an invalidation plan; expiry alone can leave changed data stale. The guidance also covers stale-while-revalidate, error responses, and cache stampedes. Shared caches should not hold sensitive user-specific data such as payment information or auth tokens.

Examples cover a TTL-backed Map, Redis with `ioredis`, Express/Hono headers, and TanStack Query. The Redis example imports `ioredis`, so that dependency matters if you adapt its code.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add zebbern/claude-code-guide --skill caching -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/caching/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/caching/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add zebbern/claude-code-guide --skill caching -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/caching/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add zebbern/claude-code-guide --skill caching -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/caching/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install zebbern/claude-code-guide caching
```

2. **Manually: put the files in place**
- File: `.github/skills/caching/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add zebbern/claude-code-guide --skill caching -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/zebbern/claude-code-guide --path skills/caching
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/caching/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add zebbern/claude-code-guide --skill caching -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/zebbern/claude-code-guide/tree/HEAD/skills/caching/SKILL.md

## When to use it
- match cache TTLs to data volatility
- include result-changing parameters in cache keys
- invalidate cached entries when source data changes
- trace stale responses and cache stampedes
- configure `staleTime` and `gcTime` in TanStack Query

## Example prompts
- Review this API's cache keys and flag any missing query parameters.
- Design an invalidation plan for cached user profiles.
- Set TanStack Query's `staleTime` and `gcTime` based on how often these results change.

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 2dba7742fef581d7.

BEGIN THIRD-PARTY FILE 2dba7742fef581d7
````text
---
name: caching
description: Caching strategies — invalidation, TTL guidelines, cache keys, cache layers, and when not to cache. Use when implementing or reviewing caching logic.
---
## WHEN_TO_USE

- When implementing a cache layer (in-memory, Redis, CDN) for an API or service.
- When choosing TTL values or invalidation strategies for cached data.
- When designing cache key schemas to avoid collisions or stale-data bugs.
- When reviewing code that reads from or writes to any cache.
- When debugging stale data, cache stampedes, or inconsistent responses.
- When configuring TanStack Query `staleTime`/`gcTime` for client-side caching.

## INVALIDATION

- [P0-MUST] Define an invalidation strategy for every cache. Stale data is worse than no cache.
- [P0-MUST] Invalidate caches when the underlying data changes — do not rely solely on TTL expiry.
- [P1-SHOULD] Prefer event-driven invalidation (on write/update/delete) over time-based expiry alone.
- [P1-SHOULD] Use cache versioning (include a version key) when data schemas change.

## TTL_GUIDELINES

- [P1-SHOULD] Set TTLs based on data volatility: static config (hours/days), user profiles (minutes), real-time data (seconds or no cache).
- [P1-SHOULD] Use stale-while-revalidate: serve stale data immediately while refreshing in the background.
- [P2-MAY] Use shorter TTLs in development and longer TTLs in production.

## CACHE_KEYS

- [P0-MUST] Include all query parameters that affect the result in the cache key.
- [P1-SHOULD] Use a consistent key format: `<entity>:<id>:<variant>` (e.g., `user:123:profile`, `products:list:page=2`).
- [P1-SHOULD] Namespace keys by service or module to prevent collisions.
- [P2-MAY] Hash long or complex keys to keep storage efficient.

## CACHE_LAYERS

- [P1-SHOULD] Use the appropriate cache layer for the use case:

| Layer | Best For | TTL Range |
|-------|----------|-----------|
| In-memory (Map, LRU) | Hot data, single-instance apps | Seconds to minutes |
| Redis / Memcached | Shared cache across instances, sessions | Minutes to hours |
| CDN / Edge | Static assets, public API responses | Hours to days |
| HTTP cache headers | Browser caching, API responses | Varies by resource |

- [P1-SHOULD] Layer caches: check memory → Redis → origin. Write-through on miss.

## WHEN_NOT_TO_CACHE

- [P0-MUST] Do not cache user-specific sensitive data (auth tokens, payment info) in shared caches.
- [P1-SHOULD] Do not cache rapidly changing data where staleness causes incorrect behavior (inventory counts, real-time pricing).
- [P1-SHOULD] Do not cache error responses — use short TTL or skip caching on failure.
- [P2-MAY] Avoid caching when the computation is cheap and the data set is small.

## CODE_EXAMPLES

### In-memory LRU cache with TTL

```ts
const cache = new Map<string, { value: unknown; expires: number }>();
const MAX_SIZE = 500;

export function getOrSet<T>(key: string, ttlMs: number, compute: () => T): T {
  const entry = cache.get(key);
  if (entry && entry.expires > Date.now()) return entry.value as T;

  const value = compute();
  if (cache.size >= MAX_SIZE) {
    // Evict oldest entry (first inserted)
````
END THIRD-PARTY FILE 2dba7742fef581d7

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