Convex Best Practices

Build production-ready Convex applications by following established patterns for function organization, query optimization, validation, TypeScript usage, and error handling.

Code Quality

All patterns in this skill comply with @convex-dev/eslint-plugin. Install it for build-time validation:

npm i @convex-dev/eslint-plugin --save-dev

// eslint.config.js
import { defineConfig } from "eslint/config";
import convexPlugin from "@convex-dev/eslint-plugin";

export default defineConfig([
  ...convexPlugin.configs.recommended,
]);

The plugin enforces four rules:

Docs: https://docs.convex.dev/eslint

Documentation Sources

Before implementing, do not assume; fetch the latest documentation:

• Primary: https://docs.convex.dev/understanding/best-practices/
• Error Handling: https://docs.convex.dev/functions/error-handling
• Write Conflicts: https://docs.convex.dev/error#1
• For broader context: https://docs.convex.dev/llms.txt

Instructions

The Zen of Convex

1. Convex manages the hard parts - Let Convex handle caching, real-time sync, and consistency
2. Functions are the API - Design your functions as your application's interface
3. Schema is truth - Define your data model explicitly in schema.ts
4. TypeScript everywhere - Leverage end-to-end type safety
5. Queries are reactive - Think in terms of subscriptions, not requests

Function Organization

Organize your Convex functions by domain:

// convex/users.ts - User-related functions
import { query, mutation } from "./_generated/server";
import { v } from "convex/values";

export const get = query({
  args: { userId: v.id("users") },
  returns: v.union(
    v.object({
      _id: v.id("users"),
      _creationTime: v.number(),
      name: v.string(),
      email: v.string(),
    }),
    v.null(),
  ),
  handler: async (ctx, args) => {
    return await ctx.db.get("users", args.userId);
  },
});

Argument and Return Validation

Always define validators for arguments AND return types:

export const createTask = mutation({
  args: {
    title: v.string(),
    description: v.optional(v.string()),
    priority: 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", {
      title: args.title,
      description: args.description,
      priority: args.priority,
      completed: false,
      createdAt: Date.now(),
    });
  },
});

Query Patterns

Use indexes instead of filters for efficient queries:

// Schema with index
export default defineSchema({
  tasks: defineTable({
    userId: v.id("users"),
    status: v.string(),
    createdAt: v.number(),
  })
    .index("by_user", ["userId"])
    .index("by_user_and_status", ["userId", "status"]),
});

// Query using index
export const getTasksByUser = query({
  args: { userId: v.id("users") },
  returns: v.array(
    v.object({
      _id: v.id("tasks"),
      _creationTime: v.number(),
      userId: v.id("users"),
      status: v.string(),
      createdAt: v.number(),
    }),
  ),
  handler: async (ctx, args) => {
    return await ctx.db
      .query("tasks")
      .withIndex("by_user", (q) => q.eq("userId", args.userId))
      .order("desc")
      .collect();
  },
});

Error Handling

Use ConvexError for user-facing errors:

import { ConvexError } from "convex/values";

export const updateTask = mutation({
  args: {
    taskId: v.id("tasks"),
    title: v.string(),
  },
  returns: v.null(),
  handler