Convex + TanStack Start Skill

Convex + TanStack Start

Overview

This skill provides guidance for building reactive, real-time full-stack applications using Convex (reactive backend-as-a-service) with TanStack Start (full-stack React meta-framework). The stack provides live-updating queries, type-safe end-to-end development, SSR support, and automatic cache invalidation.

When to Use This Skill

Implementing Convex queries, mutations, or actions
Setting up or troubleshooting Better Auth authentication
Configuring TanStack Router routes and loaders
Writing schema definitions and indexes
Implementing data fetching patterns (useQuery, useSuspenseQuery)
Working with file storage, scheduling, or cron jobs
Building AI agents with @convex-dev/agent
Debugging SSR or hydration issues

Quick Reference

Essential Imports

// Data fetching (always use cached version)
import { useQuery } from 'convex-helpers/react/cache'
import { useMutation, useAction } from 'convex/react'

// SSR with React Query
import { useSuspenseQuery } from '@tanstack/react-query'
import { convexQuery } from '@convex-dev/react-query'

// API and types
import { api } from '~/convex/_generated/api'
import type { Id, Doc } from '~/convex/_generated/dataModel'

// Backend functions
import { query, mutation, action } from "./_generated/server"
import { v } from "convex/values"

The Skip Pattern

Never call hooks conditionally. Use "skip" instead:

const user = useQuery(api.users.get, userId ? { userId } : "skip")
const org = useQuery(api.orgs.get, user?.orgId ? { orgId: user.orgId } : "skip")

Three-State Query Handling

if (data === undefined) return <Skeleton />  // Loading
if (data === null) return <NotFound />       // Not found
return <Content data={data} />               // Success

Function Syntax (Always Include Returns Validator)

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

Index Best Practices

// Schema - name includes all fields
.index("by_organizationId_status", ["organizationId", "status"])

// Query - fields in same order as index
.withIndex("by_organizationId_status", (q) =>
  q.eq("organizationId", orgId).eq("status", "published")
)

Auth Check (Backend)

import { authComponent } from "./auth"

const user = await authComponent.getAuthUser(ctx)
if (!user) throw new Error("Not authenticated")

Core Principles

Use queries for reads - Queries are reactive, cacheable, and consistent
Keep functions fast - Finish in < 100ms, work with < a few hundred records
Prefer queries/mutations over actions - Actions are for external API calls only
Always use indexes - Never do table scans with .filter()
Minimize client state - Rely on Convex's real-time sync

Common Anti-Patterns

| Wrong | Correct | |-------|---------| | import { useQuery } from 'convex/react' | import { useQuery } from 'convex-helpers/react/cache' | | if (id) useQuery(...) | useQuery(..., id ? {...} : "skip") | | .filter(x => x.field === val) | .withIndex("by_field", q => q.eq("field", val)) | | Action with ctx.db | Use ctx.runQuery/runMutation | | count || 0 | count ?? 0 (0 is falsy) |

Reference Files

Load the appropriate reference file based on the task:

| File | Use When | |------|----------| | references/01-setup.md | Project setup, config files, environment variables | | references/02-router.md | Router setup, root route, file-based routing, layouts | | references/03-auth.md | Better Auth setup, sign up/in/out, protected routes, SSR auth | | references/04-data-fetching.md | useQuery, useSuspenseQuery, mutations, loaders, prefetching | | references/05-backend.md | Schema, queries, mutations, actions, internal functions, HTTP endpoints | | references/06-types.md | TypeScript patterns, validators, type mapping | | references/07-storage.md | File upload, download, metadata, deletion | | references/08-scheduling.md | scheduler.runAfter, cron jobs | | references/09-agents.md | AI agents, tools, RAG setup | | references/10-frontend.md | Component patterns, loading states, Tailwind/shadcn | | references/11-permissions.md | Role hierarchy, feature access patterns | | references/12-deployment.md | Dev commands, Convex CLI, Vercel deployment | | references/13-quick-reference.md | Import cheatsheet, common patterns summary |

When to Load References

Starting a new project: Load 01-setup.md
Adding authentication: Load 03-auth.md
Writing backend functions: Load 05-backend.md
Implementing data fetching: Load 04-data-fetching.md
Building UI components: Load 10-frontend.md
Need quick syntax: Load 13-quick-reference.md

Agent Skills: Convex + TanStack Start

Install this agent skill to your local

Skill Files