react-native-mmkv

Name: react-native-mmkv
Author: margelo

480installs7forks

How to install react-native-mmkv?

margelo/react-native-skills/react-native-mmkv

$npx -y skills add margelo/react-native-skills --skill react-native-mmkv

Installs into the current project.

Summary

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, AsyncStora

Files · 1

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SKILL.md

1	# react-native-mmkv
2
3	A focused reference for AI coding assistants working in a project that uses `react-native-mmkv`. Answer using the real APIs from this library — not invented ones — by routing to the matching `references/*.md` file below.
4
5	## Mental model
6
7	`react-native-mmkv` is a high-performance, synchronous key-value storage library for React Native, backed by Tencent's [MMKV](https://github.com/Tencent/MMKV) C++ engine via Nitro Modules (JSI). It is ~30x faster than AsyncStorage.
8
9	The three things that trip people up:
10
11	1. Everything is synchronous. No `await`, no Promises. `storage.getString('key')` returns the value immediately. This is the whole point — MMKV memory-maps files and reads/writes in-process.
12	2. It's a key-value store, not a database. All data is cached in memory. Keep total size under ~100 MB; for larger datasets use [react-native-nitro-sqlite](https://github.com/margelo/react-native-nitro-sqlite) or WatermelonDB. There is no fixed storage limit — but memory warnings will fire if you go too large.
13	3. V4 is a breaking rewrite. The constructor changed from `new MMKV()` to `createMMKV()`, `.delete()` became `.remove()`, and `react-native-nitro-modules` is now a required peer dependency. See the [upgrade guide](./references/upgrade-v4.md).
14
15	> V4 requires React Native 0.75+. It works on both the New Architecture and the old architecture (Nitro is backwards compatible).
16
17	## Routing table — problem to reference
18
19	Load the matching file from `references/` before writing code. Each reference cites real APIs from the library.
20
21	\| User is asking about… \| Read \|
22	\|---\|---\|
23	\| Creating an MMKV instance, configuration options (`id`, `path`, `encryptionKey`, `mode`, `readOnly`, `compareBeforeSet`), the `createMMKV()` factory \| [`references/create-instance.md`](./references/create-instance.md) \|
24	\| Getting/setting values, all data types (string, number, boolean, buffer, objects via JSON), key management (`contains`, `getAllKeys`, `remove`, `clearAll`), `size`, `trim`, `importAllFrom` \| [`references/crud-operations.md`](./references/crud-operations.md) \|
25	\| React hooks (`useMMKVString`, `useMMKVNumber`, `useMMKVBoolean`, `useMMKVBuffer`, `useMMKVObject`, `useMMKV`, `useMMKVListener`, `useMMKVKeys`), reactive UI \| [`references/hooks.md`](./references/hooks.md) \|
26	\| Listening for value changes outside of React, `addOnValueChangedListener`, cleaning up listeners \| [`references/listeners.md`](./references/listeners.md) \|
27	\| Encryption (`encrypt`, `decrypt`, `recrypt`), AES-128 vs AES-256, `encryptionKey` config \| [`references/encryption.md`](./references/encryption.md) \|
28	\| Migrating from AsyncStorage, data transfer pattern, completion flag \| [`references/migrate-from-async-storage.md`](./references/migrate-from-async-storage.md) \|
29	\| zustand persist middleware, redux-persist, jotai `atomWithMMKV`, react-query persister, MobX \| [`references/state-management.md`](./references/state-management.md) \|
30	\| V4 upgrade, breaking changes from V3, `new MMKV()` → `createMMKV()`, `.delete()` → `.remove()` \| [`references/upgrade-v4.md`](./references/upgrade-v4.md) \|
31	\| Storage size limits, memory warnings, when to use a database instead \| [`references/limits-and-gotchas.md`](./references/limits-and-gotchas.md) \|
32
33	If the question doesn't match any row, read [`references/create-instance.md`](./references/create-instance.md) first — most setup questions start there.
34
35	## Installation
36
37	```bash
38	npm install react-native-mmkv react-native-nitro-modules
39	cd ios && pod install
40	```
41
42	Expo:
43	```bash
44	npx expo install react-native-mmkv react-native-nitro-modules
45	npx expo prebuild
46	```
47
48	After install, rebuild the app. No additional native wiring is required.
49
50	## Quick reference — full MMKV instance API
51
52	```ts
53	import { createMMKV, existsMMKV, deleteMMKV } from 'react-native-mmkv'
54
55	const storage = createMMKV({ id: 'my-store' })
56
57	// Properties (read-only)
58	storage.id // string
59	storage.length // number of keys
60	storage.byteSize // total file size in bytes
61	storage.size // (deprecated — use byteSize)
62	storage.isReadOnly // boolean
63	storage.isEncrypted // boolean
64
65	// Write
66	storage.set('key', 'string' \| 42 \| true \| arrayBuffer)
67
68	// Read
69	storage.getString('key') // string \| undefined
70	storage.getNumber('key')

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react-native-mmkv

480installs7forks

View on GitHub

How to install react-native-mmkv?

margelo/react-native-skills/react-native-mmkv

$npx -y skills add margelo/react-native-skills --skill react-native-mmkv

Installs into the current project.

Summary

Files · 1

View on GitHub

SKILL.md

1	# react-native-mmkv
2
3	A focused reference for AI coding assistants working in a project that uses `react-native-mmkv`. Answer using the real APIs from this library — not invented ones — by routing to the matching `references/*.md` file below.
4
5	## Mental model
6
7	`react-native-mmkv` is a high-performance, synchronous key-value storage library for React Native, backed by Tencent's [MMKV](https://github.com/Tencent/MMKV) C++ engine via Nitro Modules (JSI). It is ~30x faster than AsyncStorage.
8
9	The three things that trip people up:
10
11	1. Everything is synchronous. No `await`, no Promises. `storage.getString('key')` returns the value immediately. This is the whole point — MMKV memory-maps files and reads/writes in-process.
12	2. It's a key-value store, not a database. All data is cached in memory. Keep total size under ~100 MB; for larger datasets use [react-native-nitro-sqlite](https://github.com/margelo/react-native-nitro-sqlite) or WatermelonDB. There is no fixed storage limit — but memory warnings will fire if you go too large.
13	3. V4 is a breaking rewrite. The constructor changed from `new MMKV()` to `createMMKV()`, `.delete()` became `.remove()`, and `react-native-nitro-modules` is now a required peer dependency. See the [upgrade guide](./references/upgrade-v4.md).
14
15	> V4 requires React Native 0.75+. It works on both the New Architecture and the old architecture (Nitro is backwards compatible).
16
17	## Routing table — problem to reference
18
19	Load the matching file from `references/` before writing code. Each reference cites real APIs from the library.
20
21	\| User is asking about… \| Read \|
22	\|---\|---\|
23	\| Creating an MMKV instance, configuration options (`id`, `path`, `encryptionKey`, `mode`, `readOnly`, `compareBeforeSet`), the `createMMKV()` factory \| [`references/create-instance.md`](./references/create-instance.md) \|
24	\| Getting/setting values, all data types (string, number, boolean, buffer, objects via JSON), key management (`contains`, `getAllKeys`, `remove`, `clearAll`), `size`, `trim`, `importAllFrom` \| [`references/crud-operations.md`](./references/crud-operations.md) \|
25	\| React hooks (`useMMKVString`, `useMMKVNumber`, `useMMKVBoolean`, `useMMKVBuffer`, `useMMKVObject`, `useMMKV`, `useMMKVListener`, `useMMKVKeys`), reactive UI \| [`references/hooks.md`](./references/hooks.md) \|
26	\| Listening for value changes outside of React, `addOnValueChangedListener`, cleaning up listeners \| [`references/listeners.md`](./references/listeners.md) \|
27	\| Encryption (`encrypt`, `decrypt`, `recrypt`), AES-128 vs AES-256, `encryptionKey` config \| [`references/encryption.md`](./references/encryption.md) \|
28	\| Migrating from AsyncStorage, data transfer pattern, completion flag \| [`references/migrate-from-async-storage.md`](./references/migrate-from-async-storage.md) \|
29	\| zustand persist middleware, redux-persist, jotai `atomWithMMKV`, react-query persister, MobX \| [`references/state-management.md`](./references/state-management.md) \|
30	\| V4 upgrade, breaking changes from V3, `new MMKV()` → `createMMKV()`, `.delete()` → `.remove()` \| [`references/upgrade-v4.md`](./references/upgrade-v4.md) \|
31	\| Storage size limits, memory warnings, when to use a database instead \| [`references/limits-and-gotchas.md`](./references/limits-and-gotchas.md) \|
32
33	If the question doesn't match any row, read [`references/create-instance.md`](./references/create-instance.md) first — most setup questions start there.
34
35	## Installation
36
37	```bash
38	npm install react-native-mmkv react-native-nitro-modules
39	cd ios && pod install
40	```
41
42	Expo:
43	```bash
44	npx expo install react-native-mmkv react-native-nitro-modules
45	npx expo prebuild
46	```
47
48	After install, rebuild the app. No additional native wiring is required.
49
50	## Quick reference — full MMKV instance API
51
52	```ts
53	import { createMMKV, existsMMKV, deleteMMKV } from 'react-native-mmkv'
54
55	const storage = createMMKV({ id: 'my-store' })
56
57	// Properties (read-only)
58	storage.id // string
59	storage.length // number of keys
60	storage.byteSize // total file size in bytes
61	storage.size // (deprecated — use byteSize)
62	storage.isReadOnly // boolean
63	storage.isEncrypted // boolean
64
65	// Write
66	storage.set('key', 'string' \| 42 \| true \| arrayBuffer)
67
68	// Read
69	storage.getString('key') // string \| undefined
70	storage.getNumber('key')

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Type