Supabase Edge Functions vs Next.js Route Handlers: 6 Questions to Decide Where Your Backend Code Lives

If your app runs on Next.js with Supabase, you have two obvious places to put server-side logic: a Route Handler (app/api/.../route.ts) deployed with your Next.js app, or a Supabase Edge Function (Deno, deployed with supabase functions deploy). Both can read the database, call third-party APIs and keep secrets off the client. Picking the wrong one usually doesn't break anything on day one; it just makes the code harder to move, test and secure later.

These six questions are the checklist I use.

1. Who calls this code?

• Only your Next.js frontend? A Route Handler or a Server Action is the simplest choice. It shares your types, your env vars and your deploy.
• Other clients too (a mobile app, a cron service, a webhook from Stripe or GitHub)? An Edge Function gives you one URL that doesn't depend on your web app's deploy, and it keeps working if you later split the frontend.

2. Does it need the user's session, or does it act as the system?

Inside Next.js, create the Supabase client with @supabase/ssr and the request cookies, so queries run as the signed-in user and Row Level Security applies.

In an Edge Function, forward the user's JWT: the client sends Authorization: Bearer <access_token>, and you create the client with that header so RLS still applies. Only use the service_role key for genuinely system-level work (webhooks, admin jobs), and never return its results to a user without your own checks.

Rule of thumb: if the code needs service_role, keep it as small and as far from the UI as you can. An Edge Function is a good fence for that.

3. Where does the data live, and how chatty is the code?

Edge Functions run on Supabase's infrastructure, close to your project. A function that makes many small queries in a loop often benefits from that proximity. A Route Handler on Vercel runs wherever your Vercel functions run; set the function region near your Supabase project region, or every query pays a round trip across the world.

4. What runtime do your dependencies need?

Route Handlers default to the Node.js runtime, so most npm packages just work. Edge Functions run on Deno: many npm packages work through npm: specifiers, but anything that relies on native Node add-ons or a full filesystem may not. Check your heaviest dependency (PDF generation, image processing, an SDK with native bindings) before committing.

5. How long does it run, and is it triggered by events?

Both have execution limits, and both are a poor fit for long jobs. For anything that can take minutes (video processing, large imports), return quickly and hand the work to a queue or a background job, then report progress through a table the client watches with Supabase Realtime.

Database-triggered work (react to an insert, send an email) fits Edge Functions well, invoked from a Database Webhook or pg_net, because it doesn't depend on your web app being deployed.

6. How will you test and deploy it?

Route Handlers ship with every git push and run locally with next dev. Edge Functions have their own lifecycle: supabase functions serve locally, supabase functions deploy in CI, and their own secrets set with supabase secrets set. That separation is great for shared backend logic and annoying for code that changes with every UI tweak.

A simple default

• UI-specific reads and mutations: Server Actions or Route Handlers.
• Webhooks, cross-client APIs and anything needing service_role: Edge Functions.
• Long work: a queue, with status in a table and Realtime for progress.

Disclosure

I work on Massvai, an AI app builder that generates full-stack Next.js apps with Supabase auth and data and deploys them to Vercel. The checklist above applies whether you write the code by hand or generate it.

Written for founders shipping Next.js + Supabase apps. More guides: https://massvai.com Also live: https://slugpost.com/supabase-edge-functions-vs-nextjs-route-handlers-6-questions

— Massvai Team