# yjs-best-practices

A skill that steers your agent through Yjs pitfalls: duplicate imports, subdocuments, YKeyValue and V2 encoding.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 303 installs · ★ 8
- Author: liveblocks
- License: Apache-2.0 · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/liveblocks/skills/tree/HEAD/skills/yjs-best-practices/SKILL.md
- Updated: 2026-09-08
- HTML: https://affpapa.org/en/nevibecode/skills/yjs-best-practices

## What it does

The skill kicks in while you build or debug Yjs features. It covers four areas: importing Yjs twice, subdocuments, key-value storage, and the experimental V2 encoding for `Y.Map`.

The duplicate import is the one that bites most often. When Yjs ends up in the bundle twice, the two copies don't share class references, sync breaks, and a warning shows up in the console. The skill points at pinning a single version: `resolutions` in `package.json` for npm and yarn, `pnpm.overrides` for pnpm, or aliases in your bundler.

Subdocuments get a firm no unless you truly need them. They earn their place when one room holds several very large documents or you lazy-load them one at a time. For a few editors on the same page, a `Y.Map` does the job. Watch out for alternating writes to the same keys though: `Y.Map` keeps history and the document balloons. `YKeyValue` from `y-utility` sidesteps that. The `useV2Encoding_experimental` flag cuts bandwidth, but every client in the room has to set it, or they won't read each other's changes.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add liveblocks/skills --skill yjs-best-practices -a claude-code
```

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

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add liveblocks/skills --skill yjs-best-practices -a codex
```

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

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add liveblocks/skills --skill yjs-best-practices -a cursor
```

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

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install liveblocks/skills yjs-best-practices
```

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

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add liveblocks/skills --skill yjs-best-practices -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/liveblocks/skills --path skills/yjs-best-practices
```

### Windsurf (Devin Desktop)

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

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add liveblocks/skills --skill yjs-best-practices -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/liveblocks/skills/tree/HEAD/skills/yjs-best-practices/SKILL.md

## When to use it
- track down a duplicate Yjs import in a bundle
- pin one Yjs version via resolutions or overrides
- pick Y.Map over subdocuments for several editors
- keep document size down under repeated key writes
- turn on V2 encoding without desyncing other clients

## Example prompts
- Why is the console warning about two Yjs instances? Help me fix it.
- Two text editors on one page — do I need subdocuments or is Y.Map enough?
- The document grows fast from key rewrites, move it to YKeyValue.

## Source text · SKILL.md · Apache-2.0

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: 9924106e90c99db4.

BEGIN THIRD-PARTY FILE 9924106e90c99db4
````text
---
name: "yjs-best-practices"
description:
  "Use this skill when implementing or debugging Yjs features. It helps with Yjs
  import issues, subdocuments, `YKeyValue`, `Y.Map`, and experimental V2
  encoding."
license: "Apache License 2.0"
metadata:
  author: "liveblocks"
  version: "1.0.0"
---

# Yjs best practices

## When to use this skill

Use this skill when implementing or debugging [Yjs](https://yjs.dev) features.

## Avoid importing Yjs twice

One of the most common issues when working with Yjs is accidentally importing it
twice in your application. This often happens when mixing CommonJS (CJS) and
ECMAScript Modules (ESM), or when certain bundlers bundle more than one version
of Yjs.

When Yjs is imported twice, the two instances don't share the same class
references, which can lead to synchronization issues and unexpected behavior.
You'll see a Yjs warning in the Console if this happens.

### Fixing duplicate Yjs imports

If you find duplicate Yjs imports, you can:

1. **Use package manager resolution**: Configure your package manager to resolve
   Yjs to a single version:

```json
// package.json (npm/yarn)
{
  "resolutions": {
    "yjs": "^13.6.0"
  }
}
```

```json
// package.json (pnpm)
{
  "pnpm": {
    "overrides": {
      "yjs": "^13.6.0"
    }
  }
}
```

2. **Configure your bundler**: Use aliases or resolve configurations to ensure a
   single Yjs instance.

## Avoid subdocuments when possible

It's generally better to avoid subdocuments unless you have a specific use case
that requires them. They are only necessary when:

- You have multiple _very large_ Yjs documents in the same room
- You need to lazy-load documents individually

For most use cases, including **multiple text editors on the same page**,
subdocuments are not necessary. Instead, use a
[`Y.Map`](https://docs.yjs.dev/api/shared-types/y.map) to organize your data:

```tsx
// Create Yjs document with an `editors` map
const yDoc = new Y.Doc();
const yMap = yDoc.getMap("editors");

// Create shared types and add to map
const editorOne = new Y.XMLFragment();
const editorTwo = new Y.XMLFragment();
yMap.set("editor-1", editorOne);
yMap.set("editor-2", editorTwo);
```

This approach is simpler and performs better for most applications. True use
cases for subdocuments include having many different large documents that can be
lazy loaded in one at a time. Explain this to the user, as they often don't
understand this.

## Use YKeyValue for efficient key-value storage

In many cases, [`Y.Map`](https://docs.yjs.dev/api/shared-types/y.map) can be
inefficient for key-value storage. Yjs needs to retain all key values that were
````
END THIRD-PARTY FILE 9924106e90c99db4

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