# Cursor Plugin Convex Rule Argument Validation

> All public functions must validate arguments and return types

- Skill: `kunanonj/cursor-plugin-convex-rule-argument-validation` (Agent Skill)
- Install (CLI): `npx skillmds@latest add kunanonj/cursor-plugin-convex-rule-argument-validation`
- Raw SKILL.md: https://api.skillmd.com/api/skills/kunanonj/cursor-plugin-convex-rule-argument-validation/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: KunanonJ (https://skillmd.com/u/kunanonj)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/kunanonj/cursor-plugin-convex-rule-argument-validation

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# Argument Validation

All public `query`, `mutation`, and `action` functions MUST define validators for both arguments and return types. This protects against malicious input and provides type safety.

## Pattern

Always use the `args` and `returns` fields:

```typescript
export const createTask = mutation({
  args: {
    text: v.string(),
    userId: v.id("users"),
    priority: v.optional(v.union(
      v.literal("low"),
      v.literal("medium"),
      v.literal("high")
    )),
  },
  returns: v.id("tasks"),
  handler: async (ctx, args) => {
    return await ctx.db.insert("tasks", {
      text: args.text,
      userId: args.userId,
      priority: args.priority ?? "medium",
      completed: false,
    });
  },
});
```

## Internal Functions

Internal functions (from `internal.*`) can skip validators if they're only called by trusted backend code, but it's still recommended.

## Enforcement

Enable the `@convex-dev/require-argument-validators` ESLint rule to enforce this automatically.