convex-backend – Coding skill for AI agents

Convex Backend

Use Convex to build type-safe backend logic with realtime data sync.

When to Use This Skill

Use this skill when:

• Building real-time collaborative apps (chat, dashboards, multiplayer)
• Need a backend with zero infrastructure management
• Want type-safe server functions with automatic caching
• Building AI apps that need reactive data (agent status, streaming results)
• Prototyping quickly with a managed database + functions

Prerequisites

• Node.js 18+
• npm or pnpm
• Convex account (free tier: 1M function calls/month)

Quick Start

# Initialize Convex in an existing project
npm install convex
npx convex dev     # Start local development (syncs with cloud)

# In a new project
npm create convex@latest

Schema Definition

// convex/schema.ts
import { defineSchema, defineTable } from "convex/server";
import { v } from "convex/values";

export default defineSchema({
  users: defineTable({
    name: v.string(),
    email: v.string(),
    role: v.union(v.literal("admin"), v.literal("member")),
    avatarUrl: v.optional(v.string()),
    createdAt: v.number(),
  })
    .index("by_email", ["email"])
    .index("by_role", ["role"]),

  messages: defineTable({
    userId: v.id("users"),
    channelId: v.id("channels"),
    body: v.string(),
    attachments: v.optional(v.array(v.string())),
    createdAt: v.number(),
  })
    .index("by_channel", ["channelId", "createdAt"])
    .index("by_user", ["userId"]),

  channels: defineTable({
    name: v.string(),
    description: v.optional(v.string()),
    isPrivate: v.boolean(),
  }),
});

Security completeness

The snippets below omit the application membership/ownership model and are not deployable authorization examples. Implement a shared server-side access check before listByChannel, send, paid generateResponse, upload URL generation and file URL reads. Validate identity using a stable provider subject/token identifier, not an unchecked/non-unique email. Bound body/prompt/limit values, reject missing channels and cross-tenant IDs, check external HTTP status/content shape and avoid duplicate paid requests. An isPrivate field alone enforces nothing. Use an approved dev deployment; convex dev may synchronize to cloud. Verify current quotas/pricing rather than assuming the stated free allowance.

Queries (Real-Time Reads)

// convex/messages.ts
import { query } from "./_generated/server";
import { v } from "convex/values";

export const listByChannel = query({
  args: {
    channelId: v.id("channels"),
    limit: v.optional(v.number()),
  },
  handler: async (ctx, args) => {
    const messages = await ctx.db
      .query("messages")
      .withIndex("by_channel", (q) => q.eq("channelId", args.channelId))
      .order("desc")
      .take(args.limit ?? 50);

    // Resolve user data for each message
    return Promise.all(
      messages.map(async (msg) => {
        const user = await ctx.db.get(msg.userId);
        return { ...msg, user: user ? { name: user.name, avatarUrl: user.avatarUrl } : null };
      })
    );
  },
});

Mutations (Writes)

// convex/messages.ts
import { mutation } from "./_generated/server";
import { v } from "convex/values";

export const send = mutation({
  args: {
    channelId: v.id("channels"),
    body: v.string(),
  },
  handler: async (ctx, args) => {
    const identity = await ctx.auth.getUserIdentity();
    if (!identity) throw new Error("Not authenticated");

    // Find or create user
    const user = await ctx.db
      .query("users")
      .withIndex("by_email", (q) => q.eq("email", identity.email!))
      .unique();
    if (!user) throw new Error("User not found");

    return await ctx.db.insert("messages", {
      userId: user._id,
      channelId: args.channelId,
      body: args.body,
      createdAt: Date.now(),
    });
  },
});

Actions (External APIs, AI)

// convex/ai.ts
import { action } from "./_generated/server";
import { v } from "convex/values";
import { api } from "./_generated/api";

export const generateResponse = action({
  args: { prompt: v.string(), channelId: v.id("channels") },
  handler: async (ctx, args) => {
    // Call external AI API
    const response = await fetch("https://api.anthropic.com/v1/messages", {
      method: "POST",
      headers: {
        "Content-Type": "application/json",
        "x-api-key": process.env.ANTHROPIC_API_KEY!,
        "anthropic-version": "2023-06-01",
      },
      body: JSON.stringify({
        model: "claude-sonnet-4-6",
        max_tokens: 1024,
        messages: [{ role: "user", content: args.prompt }],
      }),
    });

    const data = await response.json();
    const aiMessage = data.content[0].text;

    // Save AI response as a message via mutation
    await ctx.runMutation(api.messages.send, {
      channelId: args.channelId,
      body: aiMessage,
    });

    return aiMessage;
  },
});

Scheduled Functions (Cron Jobs)

// convex/crons.ts
import { cronJobs } from "convex/server";
import { internal } from "./_generated/api";

const crons = cronJobs();

// Run every hour
crons.interval("cleanup old messages", { hours: 1 }, internal.maintenance.cleanupOldMessages);

// Run daily at midnight UTC
crons.cron("daily report", "0 0 * * *", internal.reports.generateDailyReport);

export default crons;

Auth Integration

// convex/auth.config.ts
export default {
  providers: [
    {
      domain: process.env.AUTH_DOMAIN,
      applicationID: "convex",
    },
  ],
};

// React client setup
import { ConvexProviderWithClerk } from "convex/react-clerk";
import { ClerkProvider, useAuth } from "@clerk/clerk-react";

function App() {
  return (
    <ClerkProvider publishableKey={CLERK_KEY}>
      <ConvexProviderWithClerk client={convex} useAuth={useAuth}>
        <MyApp />
      </ConvexProviderWithClerk>
    </ClerkProvider>
  );
}

React Client Usage

// src/components/Chat.tsx
import { useQuery, useMutation } from "convex/react";
import { api } from "../convex/_generated/api";

import type { Id } from "../convex/_generated/dataModel";

export function Chat({ channelId }: { channelId: Id<"channels"> }) {
  // Real-time query — auto-updates when data changes
  const messages = useQuery(api.messages.listByChannel, { channelId });
  const sendMessage = useMutation(api.messages.send);

  const handleSend = async (body: string) => {
    await sendMessage({ channelId, body });
  };

  if (messages === undefined) return <div>Loading...</div>;

  return (
    <div>
      {messages.map((msg) => (
        <div key={msg._id}>
          <strong>{msg.user?.name}</strong>: {msg.body}
        </div>
      ))}
    </div>
  );
}

Deployment

# Deploy to production
npx convex deploy

# Deploy with environment variables
npx convex deploy --env-file .env.production

# Set environment variables
npx convex env set ANTHROPIC_API_KEY sk-ant-...
npx convex env list

# View logs
npx convex logs
npx convex logs --follow

# Run a function manually
npx convex run messages:listByChannel '{"channelId": "abc123"}'

File Storage

// convex/files.ts
import { mutation, query } from "./_generated/server";
import { v } from "convex/values";

export const generateUploadUrl = mutation(async (ctx) => {
  return await ctx.storage.generateUploadUrl();
});

export const getFileUrl = query({
  args: { storageId: v.id("_storage") },
  handler: async (ctx, args) => {
    return await ctx.storage.getUrl(args.storageId);
  },
});

Best Practices

• Define schema and validation before writing functions
• Keep mutations idempotent where possible
• Use auth identity checks in every privileged query/mutation
• Add indexes early for high-read collections
• Use internal functions for server-only logic (crons, webhooks)
• Store secrets in Convex environment variables, never in code
• Use optimistic updates in the React client for instant UI feedback

Troubleshooting

| Issue | Solution |

|-------|---------|

| Function timeout | Actions have 10min limit; break into smaller steps |

| Query too slow | Add database index matching your query pattern |

| Type errors | Run npx convex dev to regenerate types |

| Auth not working | Check auth.config.ts and provider domain |

| Deploy fails | Check npx convex logs, verify env vars are set |

Related Skills

• firebase-app-platform (firebase-app-platform) — Alternative managed backend
• vercel-deployments (vercel-deployments) — Frontend hosting
• agent-observability (agent-observability) — Instrument AI-driven backend flows

Limitations

• Infrastructure commands can disrupt services: confirm target host/scope and have backups/snapshots before mutating state.
• Docs-only import: upstream scripts and templates not bundled.