# convex-realtime

A skill for wiring React to Convex subscriptions: useQuery patterns, optimistic updates, pagination that stays live, and cutting subscription churn.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 2900 installs · ★ 405
- Author: waynesutton
- License: Apache-2.0 · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/waynesutton/builder-skills/tree/HEAD/skills/convex-realtime/SKILL.md
- Updated: 2026-09-28
- HTML: https://affpapa.org/en/nevibecode/skills/convex-realtime

## What it does

Every `useQuery` in Convex is a live subscription. The server runs the query, records the read set — documents and index ranges it touched — and pushes the result. When a mutation commits a write that overlaps that read set, the query reruns. No overlap, no rerun. The skill is built around that one rule: keep the read set small and indexed.

It walks through four cases with code. A basic `useQuery` that passes `"skip"` instead of wrapping the hook in a condition. Optimistic updates via `withOptimisticUpdate` for toggles and chat sends, including how to insert a temporary document and let the server result replace it. Pagination with `usePaginatedQuery` and `paginationOptsValidator`, where each loaded page keeps its own subscription so inserts and deletes show up without a refetch. And `useQueries` for a dynamic set of queries, such as one per id in a list.

One hard constraint: queries must be deterministic. `Date.now()`, `Math.random()` and `fetch` are not allowed inside them, because the whole subscription mechanism depends on it. `Date.now()` is fine in a client-side optimistic update. Cursors come from `.paginate()` only — building offset pagination by slicing a `.collect()` result is called out as the wrong move.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add waynesutton/builder-skills --skill convex-realtime -a claude-code
```

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

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add waynesutton/builder-skills --skill convex-realtime -a codex
```

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

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add waynesutton/builder-skills --skill convex-realtime -a cursor
```

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

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install waynesutton/builder-skills convex-realtime
```

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

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add waynesutton/builder-skills --skill convex-realtime -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/waynesutton/builder-skills --path skills/convex-realtime
```

### Windsurf (Devin Desktop)

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

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add waynesutton/builder-skills --skill convex-realtime -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/waynesutton/builder-skills/tree/HEAD/skills/convex-realtime/SKILL.md

## When to use it
- wire a React component to Convex without fighting subscriptions
- fix a list that stops updating after a server write
- stop a dashboard from rerendering on unrelated writes
- keep a load-more list live without dropped or duplicated rows
- show who is online or typing

## Example prompts
- Wire this component to Convex with useQuery so the task list updates itself
- Add an optimistic update for toggling a task in Convex
- Build live pagination for channel messages with usePaginatedQuery

## 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: 0a46f2b2e8ea0610.

BEGIN THIRD-PARTY FILE 0a46f2b2e8ea0610
````text
---
name: convex-realtime
description: Builds reactive UIs on Convex subscriptions: useQuery patterns, optimistic updates, pagination that stays live, presence, and avoiding subscription churn. Use when wiring the frontend to Convex, when data does not update live, or when a page rerenders too much.
---

# Convex realtime

Every `useQuery` is a live subscription. The one rule: keep the set of documents a query reads small and indexed, because that read set decides when the query reruns.

## When to reach for this

- Wiring a React component to Convex for the first time
- Data changes on the server but the page does not update
- A list or dashboard rerenders on every unrelated write
- A "load more" list drops or duplicates rows when new data lands
- Showing who is online or typing

## How subscriptions work

`useQuery` opens a subscription over the client's websocket. The server runs the query, records its read set (every document and index range it touched), and pushes the result. When a mutation commits a write that overlaps that read set, the server reruns the query and pushes the new result. Nothing overlaps, nothing reruns. Results are cached per function and args, so two components calling `useQuery(api.tasks.list, { userId })` share one subscription. All active subscriptions update together at the same database timestamp, so the UI never shows a half applied mutation. Queries must be deterministic for this to hold, which is why `Date.now()`, `Math.random()`, and `fetch` are not allowed inside them.

## useQuery

`undefined` means loading. Pass `"skip"` instead of wrapping the hook in a condition.

```typescript
import { useQuery } from "convex/react";
import { api } from "../convex/_generated/api";
import { Id } from "../convex/_generated/dataModel";

function TaskList({ userId }: { userId: Id<"users"> | null }) {
  const tasks = useQuery(api.tasks.list, userId ? { userId } : "skip");

  if (userId === null) return <p>Select a user</p>;
  if (tasks === undefined) return <p>Loading</p>;

  return (
    <ul>
      {tasks.map((task) => (
        <li key={task._id}>{task.title}</li>
      ))}
    </ul>
  );
}
```

Backend queries return validated data and read through an index:

```typescript
// convex/tasks.ts
import { query } from "./_generated/server";
import { v } from "convex/values";

export const list = query({
  args: { userId: v.id("users") },
  returns: v.array(
    v.object({
````
END THIRD-PARTY FILE 0a46f2b2e8ea0610

The third-party file has ended. Everything between the 0a46f2b2e8ea0610 tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

First 2431 of 10448 bytes. © waynesutton · Apache-2.0 · https://github.com/waynesutton/builder-skills/tree/HEAD/skills/convex-realtime/SKILL.md

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