React Native Mmkv

What it does

When your agent uses it

• Tasks that involve Cross-platform mobile apps
• Tasks that involve State management

Example prompts

• “/react-native-mmkv”

Requirements

• Node.js

Workflow steps

3 steps, taken from the first numbered list in SKILL.md.

1. 1Everything is synchronous. No await, no Promises. storage.getString('key') returns the value immediately. This is the whole point — MMKV…
2. 2It's a key-value store, not a database. All data is cached in memory. Keep total size under ~100 MB; for larger datasets use…
3. 3V4 is a breaking rewrite. The constructor changed from new MMKV() to createMMKV(), .delete() became .remove(), and…

What it can do on your machine

Read from SKILL.md and the folder at commit 1e9e17b. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  Shell commands in SKILL.md call:

  • npx
  • npm

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  Links to these hosts (documentation or services it may open):

  • github.com

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

React Native Mmkv loads about 2.1k tokens when it runs, and up to ~12k if it reads all its reference files. Until then it costs about 121 tokens; SKILL.md has 600 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~121

When it runs · the whole SKILL.md, loaded when a task matches

~2.1k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~12k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from margelo/react-native-skills at commit 1e9e17b, republished under its MIT licence (© margelo). 600 words, ~2,147 tokens.

name

react-native-mmkv

description

Fast synchronous key-value storage for React Native via react-native-mmkv (Nitro-backed). Covers creating and configuring MMKV instances, reading/writing all value types (string, number, boolean, buffer), React hooks for reactive UI, value-change listeners, encryption, AsyncStorage migration, and state-management integrations (zustand, redux-persist, jotai, react-query). Also covers storage limits, multi-process mode, and the V4 upgrade from the class-based API.

license

MIT

metadata.author

margelo

metadata.scope

react-native-mmkv

metadata.tags

react-native, mmkv, storage, key-value, encryption, hooks, zustand, redux, jotai, react-query, async-storage, migration, nitro-modules

npm install react-native-mmkv react-native-nitro-modules
cd ios && pod install

npx expo install react-native-mmkv react-native-nitro-modules
npx expo prebuild

import { createMMKV, existsMMKV, deleteMMKV } from 'react-native-mmkv'

const storage = createMMKV({ id: 'my-store' })

// Properties (read-only)
storage.id          // string
storage.length      // number of keys
storage.byteSize    // total file size in bytes
storage.size        // (deprecated — use byteSize)
storage.isReadOnly  // boolean
storage.isEncrypted // boolean

// Write
storage.set('key', 'string' | 42 | true | arrayBuffer)

// Read
storage.getString('key')   // string | undefined
storage.getNumber('key')   // number | undefined
storage.getBoolean('key')  // boolean | undefined
storage.getBuffer('key')   // ArrayBuffer | undefined

// Keys
storage.contains('key')    // boolean
storage.getAllKeys()        // string[]
storage.remove('key')      // boolean  (NOTE: was .delete() in V3)
storage.clearAll()         // void

// Encryption
storage.encrypt('password')
storage.encrypt('password', 'AES-256')
storage.decrypt()
storage.recrypt('newPassword' | undefined)  // (deprecated — use encrypt()/decrypt())

// Maintenance
storage.trim()                       // free unused space
storage.importAllFrom(otherStorage)  // returns count imported

// Listeners
const sub = storage.addOnValueChangedListener((key) => { ... })
sub.remove()

// Static helpers
existsMMKV('my-store')   // boolean
deleteMMKV('my-store')   // boolean

© margelo, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 9 other files (references) in skills/react-native-mmkv of margelo/react-native-skills.

• SKILL.md
• references/create-instance.md
• references/crud-operations.md
• references/encryption.md
• references/hooks.md
• references/limits-and-gotchas.md
• references/listeners.md
• references/migrate-from-async-storage.md
• references/state-management.md
• references/upgrade-v4.md

Open the folder on GitHubat commit 1e9e17b