Convex Backend Guidelines
When to Load
- Trigger: Convex-specific development, writing Convex functions, schemas, queries, mutations, actions, or real-time subscriptions
- Skip: Project does not use Convex as its backend
Comprehensive guide for building Convex backends with TypeScript. Covers function syntax, validators, schemas, queries, mutations, actions, scheduling, and file storage.
When to Apply
Reference these guidelines when:
- Writing new Convex functions (queries, mutations, actions)
- Defining database schemas and validators
- Implementing real-time data fetching
- Setting up cron jobs or scheduled functions
- Working with file storage
- Designing API structure
Rule Categories
| Category | Impact | Description |
|---|---|---|
| Function Syntax | CRITICAL | New function syntax with args/returns/handler |
| Validators | CRITICAL | Type-safe argument and return validation |
| Schema Design | HIGH | Table definitions, indexes, system fields |
| Query Patterns | HIGH | Efficient data fetching with indexes |
| Mutation Patterns | MEDIUM | Database writes, patch vs replace |
| Action Patterns | MEDIUM | External API calls, Node.js runtime |
| Scheduling | MEDIUM | Crons and delayed function execution |
| File Storage | LOW | Blob storage and metadata |
Quick Reference
Function Registration
// Public functions (exposed to clients)
import { query, mutation, action } from "./_generated/server";
// Internal functions (only callable from other Convex functions)
import {
internalQuery,
internalMutation,
internalAction,
} from "./_generated/server";Function Syntax (Always Use This)
export const myFunction = query({
args: { name: v.string() },
returns: v.string(),
handler: async (ctx, args) => {
return "Hello " + args.name;
},
});Common Validators
| Type | Validator | Example |
|---|---|---|
| String | v.string() | "hello" |
| Number | v.number() | 3.14 |
| Boolean | v.boolean() | true |
| ID | v.id("tableName") | doc._id |
| Array | v.array(v.string()) | ["a", "b"] |
| Object | v.object({...}) | {name: "x"} |
| Optional | v.optional(v.string()) | undefined |
| Union | v.union(v.string(), v.number()) | "x" or 1 |
| Literal | v.literal("status") | "status" |
| Null | v.null() | null |
Function References
// Public functions
import { api } from "./_generated/api";
api.example.myQuery; // convex/example.ts → myQuery
// Internal functions
import { internal } from "./_generated/api";
internal.example.myInternalMutation;Query with Index
// Schema
messages: defineTable({...}).index("by_channel", ["channelId"])
// Query
await ctx.db
.query("messages")
.withIndex("by_channel", (q) => q.eq("channelId", channelId))
.order("desc")
.take(10);Key Rules
- Always include
argsandreturnsvalidators on all functions - Use
v.null()for void returns - never omit return validator - Use
withIndex()notfilter()- define indexes in schema - Use
internalQuery/Mutation/Actionfor private functions - Actions cannot access
ctx.db- use runQuery/runMutation instead - Include type annotations when calling functions in same file
Full Compiled Document
For the complete guide with all rules and detailed code examples, see: AGENTS.md