supabase-hello-worldClaude Skill

Supabase Hello World — First Query

Overview

Execute your first real Supabase query: create a todos table in the dashboard, insert a row with the JS client, and read it back. This validates that your project URL, anon key, and Row Level Security are configured correctly before you build anything else.

Prerequisites

• Completed supabase-install-auth setup (project URL + anon key in .env)
• @supabase/supabase-js v2+ installed (npm install @supabase/supabase-js)
• A Supabase project at supabase.com/dashboard

Instructions

Step 1: Create the todos Table

Open your Supabase dashboard SQL Editor and run:

-- Create a simple todos table
create table public.todos (
  id bigint generated always as identity primary key,
  task text not null,
  is_complete boolean default false,
  inserted_at timestamptz default now()
);

-- Enable Row Level Security (required for anon key access)
alter table public.todos enable row level security;

-- Allow anyone with the anon key to read and insert
-- (permissive for hello-world; lock down before production)
create policy "Allow public read" on public.todos
  for select using (true);

create policy "Allow public insert" on public.todos
  for insert with check (true);

Verify the table appears under Table Editor in the dashboard before continuing.

Step 2: Insert a Row

import { createClient } from '@supabase/supabase-js'

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

// Insert a row and return it with .select()
const { data, error } = await supabase
  .from('todos')
  .insert({ task: 'Hello from Supabase!' })
  .select()

if (error) {
  console.error('Insert failed:', error.message)
  // e.g. "new row violates row-level security policy"
  process.exit(1)
}

console.log('Inserted:', data)
// [{ id: 1, task: "Hello from Supabase!", is_complete: false, inserted_at: "2026-03-22T..." }]

Key detail: .insert() alone returns { data: null }. You must chain .select() to get the inserted row back.

Step 3: Read It Back

// Select all rows from todos
const { data: todos, error: selectError } = await supabase
  .from('todos')
  .select('*')

if (selectError) {
  console.error('Select failed:', selectError.message)
  process.exit(1)
}

console.log('Todos:', todos)
// [{ id: 1, task: "Hello from Supabase!", is_complete: false, inserted_at: "2026-03-22T..." }]

// Verify the round-trip
if (todos && todos.length > 0) {
  console.log('Round-trip verified — row exists in database')
} else {
  console.error('No rows returned. Check RLS policies.')
}

Open the Table Editor in the Supabase dashboard to visually confirm the row is there.

Output

• todos table created with RLS enabled
• One row inserted via the JS client
• Same row read back with .select('*')
• Dashboard confirms the data round-trip

Error Handling

Error	Cause	Solution
relation "public.todos" does not exist	Table not created	Run the Step 1 SQL in the dashboard SQL Editor
new row violates row-level security policy	RLS blocks the insert	Add the permissive insert policy from Step 1
Invalid API key	Wrong anon key in .env	Copy from Settings > API in the dashboard
FetchError: request to https://... failed	Wrong project URL	Verify SUPABASE_URL matches dashboard URL
data is null after insert	Missing .select() chain	Add .select() after .insert()
Empty array returned from select	RLS blocks reads	Add the select policy from Step 1

Examples

TypeScript (Complete Script)

import { createClient } from '@supabase/supabase-js'

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

async function helloSupabase() {
  // Insert
  const { data: inserted, error: insertErr } = await supabase
    .from('todos')
    .insert({ task: 'Hello from TypeScript!' })
    .select()
    .single()

  if (insertErr) throw new Error(`Insert: ${insertErr.message}`)
  console.log('Inserted:', inserted)

  // Read back
  const { data: rows, error: selectErr } = await supabase
    .from('todos')
    .select('*')
    .order('inserted_at', { ascending: false })
    .limit(5)

  if (selectErr) throw new Error(`Select: ${selectErr.message}`)
  console.log('Recent todos:', rows)
}

helloSupabase().catch(console.error)

Python

from supabase import create_client
import os

supabase = create_client(
    os.environ["SUPABASE_URL"],
    os.environ["SUPABASE_ANON_KEY"]
)

# Insert a row
result = supabase.table("todos").insert({"task": "Hello from Python!"}).execute()
print("Inserted:", result.data)
# [{"id": 2, "task": "Hello from Python!", "is_complete": False, ...}]

# Read it back
result = supabase.table("todos").select("*").execute()
print("All todos:", result.data)

Install the Python client with: pip install supabase

Resources

• Supabase Getting Started
• JS Client — Insert
• JS Client — Select
• Python Client
• Row Level Security

Next Steps

Proceed to supabase-local-dev-loop for local development workflow with the Supabase CLI.