Seed a Next.js + Supabase App with Realistic Test Data

The Setup

You have a Next.js App Router project with a Supabase Postgres backend. You want 100 users, 500 posts, and 2,000 comments that are relationally consistent — locally and in CI.

Seed Script

// scripts/seed.ts
import { createClient } from "@supabase/supabase-js";

const supabase = createClient(
  process.env.SUPABASE_URL!,
  process.env.SUPABASE_SERVICE_ROLE_KEY!
);

const res = await fetch("https://api.mockhero.dev/api/v1/generate", {
  method: "POST",
  headers: {
    "Content-Type": "application/json",
    "x-api-key": process.env.MOCKHERO_API_KEY!,
  },
  body: JSON.stringify({
    seed: 42,
    tables: [
      { name: "profiles", count: 100, fields: [
        { name: "id", type: "uuid" },
        { name: "full_name", type: "full_name" },
        { name: "email", type: "email" }
      ]},
      { name: "posts", count: 500, fields: [
        { name: "id", type: "uuid" },
        { name: "user_id", type: "ref", ref: "profiles.id" },
        { name: "title", type: "sentence" },
        { name: "body", type: "paragraphs" }
      ]},
      { name: "comments", count: 2000, fields: [
        { name: "id", type: "uuid" },
        { name: "post_id", type: "ref", ref: "posts.id" },
        { name: "author_id", type: "ref", ref: "profiles.id" },
        { name: "body", type: "paragraph" }
      ]}
    ]
  })
});

const data = await res.json();
await supabase.from("profiles").insert(data.profiles);
await supabase.from("posts").insert(data.posts);
await supabase.from("comments").insert(data.comments);

RLS Note

Use the service-role key in the seed script — anon key inserts will be blocked by RLS. Never ship the service-role key to the browser.

Run It

npx tsx scripts/seed.ts

Why This Is Better Than Manual INSERTs

• Foreign keys wired automatically via ref.
• Deterministic — same seed gives identical data on every run.
• One file, readable in code review.

Get Started

Sign up free and drop this script into your Next.js repo.