# convex-functions

Writes Convex queries, mutations and actions in the object form, with args and returns validators, correct ctx usage and runtime boundaries.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 3200 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-functions/SKILL.md
- Updated: 2026-09-28
- HTML: https://affpapa.org/en/nevibecode/skills/convex-functions

## What it does

The skill kicks in when you touch a file under `convex/` that exports a function, or when you are stuck choosing between query, mutation and action. It carries a table that picks the type by what the handler touches. Queries read, mutations write, actions call out. Default to query or mutation; reach for an action only when the handler has to talk to something outside Convex.

The object form is the core rule. Every function declares `args` and `returns`, and one that returns nothing declares `returns: v.null()` and returns `null`. For reads the skill pushes `withIndex` against an index from `convex/schema.ts` and rules out `.filter()` on a table query, since that scans the whole table. Which terminal method to use — `.unique()`, `.first()`, `.take(n)`, `.collect()` or `.paginate(opts)` — follows from how many documents you expect.

Internal functions get their own section. Public `query`, `mutation` and `action` can be called by anyone with the deployment URL, so crons and privileged writes belong in `internalQuery`, `internalMutation` and `internalAction`. Schedule `internal.*` only: a scheduled function runs without a client, so a public reference there skips the auth checks a client call would hit. Actions have no `ctx.db` — reads go through `ctx.runQuery`, writes through `ctx.runMutation`, and each call is its own transaction. A file starting with `"use node";` can export actions only.

## Install

### Claude Code (native platform)

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

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

### Codex

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

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

### Cursor

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

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

### GitHub Copilot

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

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

### Gemini CLI

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

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

### Windsurf (Devin Desktop)

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

### OpenCode

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

## When to use it
- decide between query, mutation and action for a new handler
- add args and returns validators to an existing function
- swap a `.filter()` call for an indexed query
- move a privileged write into an internal mutation
- figure out why an action cannot see `ctx.db`

## Example prompts
- Add a mutation to `convex/tasks.ts` that marks a task complete, with args and returns validators
- Rewrite this query to use `withIndex` instead of `.filter()` — I need the last 50 tasks for a user
- I need to call a third-party API when an order is paid: write an action and schedule an internal mutation to save the result

## 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: 340ca0bbb9c8a2cd.

BEGIN THIRD-PARTY FILE 340ca0bbb9c8a2cd
````text
---
name: convex-functions
description: Writes Convex queries, mutations, actions, and internal functions in the object form with args and returns validators, correct ctx usage, runtime boundaries, and error handling. Use when adding or changing anything in convex/*.ts that exports a function, or when deciding between query, mutation, and action.
---

# Convex functions

Every exported function in `convex/` uses the object form with `args` and `returns` validators. Pick the type by what the handler touches: queries read, mutations write, actions call out.

## Pick the function type

| Type | Database | External calls | Callable by | Use for |
| --- | --- | --- | --- | --- |
| `query` | Read | No | Clients, other functions | Reads. Cached and reactive. |
| `mutation` | Read and write | No | Clients, other functions | Writes. One transaction. |
| `action` | Only via `runQuery` and `runMutation` | Yes | Clients, scheduler, other actions | `fetch`, third party SDKs, Node APIs |
| `internalQuery`, `internalMutation`, `internalAction` | Same as the public form | Same | Only other Convex functions | Scheduled work, crons, privileged writes |
| `httpAction` | Only via `runQuery` and `runMutation` | Yes | HTTP requests in `convex/http.ts` | Webhooks, REST endpoints |

Default to query or mutation. Reach for an action only when the handler must talk to something outside Convex.

## The object form

Declare `args` and `returns` on every function. A function that returns nothing declares `returns: v.null()` and returns `null`. Hoist a shared document validator when several functions return the same shape.

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

const taskValidator = v.object({
  _id: v.id("tasks"),
  _creationTime: v.number(),
  userId: v.id("users"),
  title: v.string(),
  completed: v.boolean(),
});

export const get = query({
  args: { taskId: v.id("tasks") },
  returns: v.union(taskValidator, v.null()),
  handler: async (ctx, args) => {
    return await ctx.db.get(args.taskId);
  },
});

export const remove = mutation({
````
END THIRD-PARTY FILE 340ca0bbb9c8a2cd

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