Building Type-Safe APIs with Next.js 15 and Drizzle ORM

In the modern web development landscape, type safety isn't just a nice-to-have — it's essential. This guide walks you through building fully type-safe API routes using Next.js 15's App Router and Drizzle ORM.

Why Type Safety Matters

When your database schema, API handlers, and frontend components all share the same type definitions, entire categories of bugs simply vanish. No more undefined is not a function in production.

Setting Up Drizzle ORM

First, let's define our schema:

import { sqliteTable, text, integer } from "drizzle-orm/sqlite-core";

export const posts = sqliteTable("posts", {
  id: text("id").primaryKey(),
  title: text("title").notNull(),
  content: text("content").notNull(),
  createdAt: integer("created_at", { mode: "timestamp" }).notNull(),
});

Creating Type-Safe API Routes

With Next.js 15 App Router, we can create API routes that leverage our Drizzle types:

import { db } from "@/lib/db";
import { posts } from "@/lib/db/schema";
import { NextResponse } from "next/server";

export async function GET() {
  const allPosts = await db.select().from(posts);
  return NextResponse.json(allPosts);
}

The beauty here is that allPosts is fully typed — your IDE knows exactly what fields are available.

Runtime Validation

While TypeScript gives us compile-time safety, we also need runtime validation for incoming data. Here's how to add that layer:

export async function POST(request: Request) {
  const body = await request.json();
  
  if (!body.title || !body.content) {
    return NextResponse.json(
      { error: "Title and content are required" },
      { status: 400 }
    );
  }

  const newPost = await db.insert(posts).values({
    id: crypto.randomUUID(),
    title: body.title,
    content: body.content,
    createdAt: new Date(),
  }).returning();

  return NextResponse.json(newPost[0], { status: 201 });
}

Conclusion

Type-safe APIs aren't just about preventing bugs — they're about developer experience. When your entire stack speaks the same type language, development becomes faster and more enjoyable.