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Next.js SaaS MVP rules: AGENTS.md, CLAUDE.md & Cursor rules
A SaaS MVP has three places where AI shortcuts hurt: auth, payments, and secrets. These rules keep the AI on the boring, safe path for all three.
Stack these rules assume: Next.js (App Router), TypeScript, a hosted auth provider, Stripe for payments. Different stack? Customize it in the generator.
Want the full step-by-step kit?
MVP Spec-to-Build Pack ($7): A fill-in 1-page spec, a landing page prompt, a 7-prompt build sequence in the right order, a "did I leak user data?" checklist, and cheap fix-it prompts.
Get the kit for $7 on Gumroad → See what's inside
or get all 5 kits for $25 (save $14) →
One markdown file, instant download. 7-day refund, no questions asked.
Quick start
- Copy the
AGENTS.mdbelow into your project's root folder. - Fill in the three
[bracketed]lines under "Project". Delete any rule that doesn't fit. - Start your first chat with: "Read AGENTS.md and follow it for this whole session."
AGENTS.md (works across tools)
Read by OpenAI Codex, Cursor, GitHub Copilot, Claude Code (when there's no CLAUDE.md) and many other agents.
# AGENTS.md: Next.js SaaS MVP
Instructions for AI coding agents working on this project. Replace anything in [brackets].
## Project
- What it is: [one sentence: what you are building and who it is for]
- Stack: Next.js (App Router), TypeScript, a hosted auth provider, Stripe for payments
- Version 1 only needs to: [the ONE thing it must do]
## Commands
- Create the project: `npx create-next-app@latest`
- Run locally: `npm run dev`
- Production build (catches type errors): `npm run build`
- Lint: `npm run lint`
## Project rules
- Use the App Router (the app/ directory). Don't mix in the old pages/ router unless I ask.
- Never build our own password storage or session system. Use the auth provider we chose.
- Only variables prefixed NEXT_PUBLIC_ may be used in client components. Everything else stays server-side.
- Payments use Stripe Checkout or Stripe-hosted pages. Prices come from the server, never from the client.
- Run npm run build before saying a task is done.
- Keep v1 to the core loop: sign up, do the one main thing, pay. Ask before adding settings pages, teams, or admin panels.
## How to work
- Do one task per request. If my request is really several tasks, list them and do only the first.
- Before writing code, give a 3-line plan: what you'll change, which files, and how I'll test it.
- Make the smallest change that works. Don't refactor, rename, or reformat code I didn't ask about.
- Ask before adding a dependency, deleting or moving files, changing the data/database structure, or touching more than 3 files.
- If you're not sure a library, API, or setting exists in the version we use, say so and check the installed package or the docs instead of guessing.
- Never say something works unless you ran it or I confirmed it. Report errors exactly.
- Secrets (API keys, tokens, passwords) live only in environment variables or a .env file listed in .gitignore. Never print, hardcode, or commit them.
- Never run destructive commands (rm -rf, git reset --hard, force-push, dropping tables) without asking first.
## Finish every task with
1. What changed (list the files).
2. How to run or test it in under a minute, and what I should see.
3. A suggested git commit message.
Want the full step-by-step kit?
MVP Spec-to-Build Pack ($7): A fill-in 1-page spec, a landing page prompt, a 7-prompt build sequence in the right order, a "did I leak user data?" checklist, and cheap fix-it prompts.
Get the kit for $7 on Gumroad → See what's inside
or get all 5 kits for $25 (save $14) →
One markdown file, instant download. 7-day refund, no questions asked.
Why each rule exists
- Next.js SaaS MVP ruleUse the App Router (the app/ directory). Don't mix in the old pages/ router unless I ask.Why: Mixing routers gives you two ways of doing everything, and the AI will use both.
- Next.js SaaS MVP ruleNever build our own password storage or session system. Use the auth provider we chose.Why: Hand-rolled auth is where serious security bugs live. Providers have already solved it.
- Next.js SaaS MVP ruleOnly variables prefixed NEXT_PUBLIC_ may be used in client components. Everything else stays server-side.Why: Next.js inlines NEXT_PUBLIC_ variables into the browser bundle. A secret with that prefix is public.
- Next.js SaaS MVP rulePayments use Stripe Checkout or Stripe-hosted pages. Prices come from the server, never from the client.Why: If the browser can send the price, someone will send $0.
- Next.js SaaS MVP ruleRun npm run build before saying a task is done.Why: next dev forgives type errors that will fail your deploy. The build doesn't.
- Next.js SaaS MVP ruleKeep v1 to the core loop: sign up, do the one main thing, pay. Ask before adding settings pages, teams, or admin panels.Why: MVPs die from scope creep, not from missing features.
- How to workDo one task per request. If my request is really several tasks, list them and do only the first.Why: Big multi-part requests are where AI tools change 12 files and you can't tell which change broke things.
- How to workBefore writing code, give a 3-line plan: what you'll change, which files, and how I'll test it.Why: A plan you can read in 10 seconds catches the wrong approach before it costs you an hour or a pile of credits.
- How to workMake the smallest change that works. Don't refactor, rename, or reformat code I didn't ask about.Why: Drive-by "cleanups" are the #1 cause of "it was working yesterday".
- How to workAsk before adding a dependency, deleting or moving files, changing the data/database structure, or touching more than 3 files.Why: These are the changes that are hard to undo. One quick question is cheaper than a rollback.
- How to workIf you're not sure a library, API, or setting exists in the version we use, say so and check the installed package or the docs instead of guessing.Why: AI tools confidently invent functions and config options. Making it check is the cure.
- How to workNever say something works unless you ran it or I confirmed it. Report errors exactly.Why: "Should work now" isn't a test result. You want facts, not optimism.
- How to workSecrets (API keys, tokens, passwords) live only in environment variables or a .env file listed in .gitignore. Never print, hardcode, or commit them.Why: Leaked keys get found by bots within minutes of a public push. This rule is the cheapest insurance you'll ever buy.
- How to workNever run destructive commands (rm -rf, git reset --hard, force-push, dropping tables) without asking first.Why: One bad command can delete the only copy of your work.
- Finish every task withWhat changed, how to test it, and a commit message.Why: This turns every task into a checkpoint: you test it, you commit it, and you always have a last good version to go back to.
Use it as CLAUDE.md (Claude Code)
Pick one:
- Do nothing. Current Claude Code versions read
AGENTS.mdwhen the project has noCLAUDE.md. Run/memoryin a session to check it loaded. - Import it (best if you want Claude-only extras, or you're on an older Claude Code). Create
CLAUDE.mdnext toAGENTS.md:
@AGENTS.md
## Claude Code
- Use plan mode before any change that touches more than 3 files.
- Claude only? Save the same AGENTS.md text as
CLAUDE.mdinstead. Don't keep two separate copies; they drift apart.
Heads-up: if a project has both files and CLAUDE.md doesn't import AGENTS.md, Claude Code reads only CLAUDE.md by default. More in AGENTS.md vs CLAUDE.md.
Use it as Cursor rules (.cursor/rules/*.mdc)
Cursor reads AGENTS.md too, so the file above already works. If you prefer Cursor's own Project Rules, split it into two .mdc files. The .mdc extension and frontmatter are required; Cursor ignores plain .md files in .cursor/rules.
---
description: Project overview and working rules for Next.js SaaS MVP
alwaysApply: true
---
# Next.js SaaS MVP
Instructions for AI coding agents working on this project. Replace anything in [brackets].
## Project
- What it is: [one sentence: what you are building and who it is for]
- Stack: Next.js (App Router), TypeScript, a hosted auth provider, Stripe for payments
- Version 1 only needs to: [the ONE thing it must do]
## Commands
- Create the project: `npx create-next-app@latest`
- Run locally: `npm run dev`
- Production build (catches type errors): `npm run build`
- Lint: `npm run lint`
## How to work
- Do one task per request. If my request is really several tasks, list them and do only the first.
- Before writing code, give a 3-line plan: what you'll change, which files, and how I'll test it.
- Make the smallest change that works. Don't refactor, rename, or reformat code I didn't ask about.
- Ask before adding a dependency, deleting or moving files, changing the data/database structure, or touching more than 3 files.
- If you're not sure a library, API, or setting exists in the version we use, say so and check the installed package or the docs instead of guessing.
- Never say something works unless you ran it or I confirmed it. Report errors exactly.
- Secrets (API keys, tokens, passwords) live only in environment variables or a .env file listed in .gitignore. Never print, hardcode, or commit them.
- Never run destructive commands (rm -rf, git reset --hard, force-push, dropping tables) without asking first.
## Finish every task with
1. What changed (list the files).
2. How to run or test it in under a minute, and what I should see.
3. A suggested git commit message.
The project rules only attach when a matching file is in the chat (globs with alwaysApply: false). Want them on all the time? Change it to alwaysApply: true.
---
globs: app/**/*.tsx, app/**/*.ts, src/**/*.ts, src/**/*.tsx
alwaysApply: false
---
# Project rules: Next.js SaaS MVP
- Use the App Router (the app/ directory). Don't mix in the old pages/ router unless I ask.
- Never build our own password storage or session system. Use the auth provider we chose.
- Only variables prefixed NEXT_PUBLIC_ may be used in client components. Everything else stays server-side.
- Payments use Stripe Checkout or Stripe-hosted pages. Prices come from the server, never from the client.
- Run npm run build before saying a task is done.
- Keep v1 to the core loop: sign up, do the one main thing, pay. Ask before adding settings pages, teams, or admin panels.
Use either AGENTS.md or these .mdc files, not both, so you don't send the same rules twice. See Cursor rules vs AGENTS.md.
Use it in Lovable or Bolt
Browser builders don't read files from your computer, so paste the rules into the project's persistent instructions:
- Lovable: Project settings → Knowledge (up to 10,000 characters). This version is 2,042 characters. If your Lovable project is connected to GitHub, Lovable's docs say it also reads a root-level
AGENTS.md. - Bolt: Project settings → Knowledge.
This version drops the Commands section, since the builder runs the project for you.
# Project rules: Next.js SaaS MVP
Instructions for AI coding agents working on this project. Replace anything in [brackets].
## Project
- What it is: [one sentence: what you are building and who it is for]
- Stack: Next.js (App Router), TypeScript, a hosted auth provider, Stripe for payments
- Version 1 only needs to: [the ONE thing it must do]
## Project rules
- Use the App Router (the app/ directory). Don't mix in the old pages/ router unless I ask.
- Never build our own password storage or session system. Use the auth provider we chose.
- Only variables prefixed NEXT_PUBLIC_ may be used in client components. Everything else stays server-side.
- Payments use Stripe Checkout or Stripe-hosted pages. Prices come from the server, never from the client.
- Run npm run build before saying a task is done.
- Keep v1 to the core loop: sign up, do the one main thing, pay. Ask before adding settings pages, teams, or admin panels.
## How to work
- Do one task per request. If my request is really several tasks, list them and do only the first.
- Before writing code, give a 3-line plan: what you'll change, which files, and how I'll test it.
- Make the smallest change that works. Don't refactor, rename, or reformat code I didn't ask about.
- Ask before adding a dependency, deleting or moving files, changing the data/database structure, or touching more than 3 files.
- If you're not sure a library, API, or setting exists in the version we use, say so and check the installed package or the docs instead of guessing.
- Never say something works unless you ran it or I confirmed it. Report errors exactly.
- Secrets (API keys, tokens, passwords) live only in environment variables or a .env file listed in .gitignore. Never print, hardcode, or commit them.
- Never run destructive commands (rm -rf, git reset --hard, force-push, dropping tables) without asking first.
## Finish every task with
1. What changed (list the files).
2. How to run or test it in under a minute, and what I should see.
3. A suggested git commit message.
Building this in a browser app builder? These rules work as Project Knowledge in both. Try Bolt · Try Lovable
Disclosure: the Bolt link is an affiliate (referral) link. If you sign up or buy through it, VibeKits may earn a commission at no extra cost to you. The Lovable link is a plain link. It never changes our pick.
Related
- Best AI tool to build a web app MVP (which tool to use, real prices)
- Lovable vs Bolt vs Replit for beginners (honest picks, real prices)
- AGENTS.md, CLAUDE.md and Cursor rules formats explained