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
args and returns validators on all functions
- Use
v.null() for void returns - never omit return validator
- Use
withIndex() not filter() - define indexes in schema
- Use
internalQuery/Mutation/Action for 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
1---2name: convex-backend3description: Convex backend development guidelines. Use when writing Convex functions, schemas, queries, mutations, actions, or any backend code in a Convex project. Triggers on tasks involving Convex database operations, real-time subscriptions, file storage, or serverless functions.4---56# Convex Backend Guidelines78### When to Load910- **Trigger**: Convex-specific development, writing Convex functions, schemas, queries, mutations, actions, or real-time subscriptions11- **Skip**: Project does not use Convex as its backend1213Comprehensive guide for building Convex backends with TypeScript. Covers function syntax, validators, schemas, queries, mutations, actions, scheduling, and file storage.1415## When to Apply1617Reference these guidelines when:1819- Writing new Convex functions (queries, mutations, actions)20- Defining database schemas and validators21- Implementing real-time data fetching22- Setting up cron jobs or scheduled functions23- Working with file storage24- Designing API structure2526## Rule Categories2728| Category | Impact | Description |29| ----------------- | -------- | --------------------------------------------- |30| Function Syntax | CRITICAL | New function syntax with args/returns/handler |31| Validators | CRITICAL | Type-safe argument and return validation |32| Schema Design | HIGH | Table definitions, indexes, system fields |33| Query Patterns | HIGH | Efficient data fetching with indexes |34| Mutation Patterns | MEDIUM | Database writes, patch vs replace |35| Action Patterns | MEDIUM | External API calls, Node.js runtime |36| Scheduling | MEDIUM | Crons and delayed function execution |37| File Storage | LOW | Blob storage and metadata |3839## Quick Reference4041### Function Registration4243```typescript44// Public functions (exposed to clients)45import { query, mutation, action } from "./_generated/server";4647// Internal functions (only callable from other Convex functions)48import {49 internalQuery,50 internalMutation,51 internalAction,52} from "./_generated/server";53```5455### Function Syntax (Always Use This)5657```typescript58export const myFunction = query({59 args: { name: v.string() },60 returns: v.string(),61 handler: async (ctx, args) => {62 return "Hello " + args.name;63 },64});65```6667### Common Validators6869| Type | Validator | Example |70| -------- | --------------------------------- | ------------- |71| String | `v.string()` | `"hello"` |72| Number | `v.number()` | `3.14` |73| Boolean | `v.boolean()` | `true` |74| ID | `v.id("tableName")` | `doc._id` |75| Array | `v.array(v.string())` | `["a", "b"]` |76| Object | `v.object({...})` | `{name: "x"}` |77| Optional | `v.optional(v.string())` | `undefined` |78| Union | `v.union(v.string(), v.number())` | `"x"` or `1` |79| Literal | `v.literal("status")` | `"status"` |80| Null | `v.null()` | `null` |8182### Function References8384```typescript85// Public functions86import { api } from "./_generated/api";87api.example.myQuery; // convex/example.ts → myQuery8889// Internal functions90import { internal } from "./_generated/api";91internal.example.myInternalMutation;92```9394### Query with Index9596```typescript97// Schema98messages: defineTable({...}).index("by_channel", ["channelId"])99100// Query101await ctx.db102 .query("messages")103 .withIndex("by_channel", (q) => q.eq("channelId", channelId))104 .order("desc")105 .take(10);106```107108### Key Rules1091101. **Always include `args` and `returns` validators** on all functions1112. **Use `v.null()` for void returns** - never omit return validator1123. **Use `withIndex()` not `filter()`** - define indexes in schema1134. **Use `internalQuery/Mutation/Action`** for private functions1145. **Actions cannot access `ctx.db`** - use runQuery/runMutation instead1156. **Include type annotations** when calling functions in same file116117## Full Compiled Document118119For the complete guide with all rules and detailed code examples, see: `AGENTS.md`120
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