Two-sided marketplace: what to build it with and what it costs

Sellers list, buyers buy, and you take a cut, with payouts, reviews, search and messaging.

Sample PRD

Seller and buyer accounts
Listings with photos
Search
Messaging
Reviews
Payouts to sellers

What it needs

Marketplace payouts to third parties: pay sellers and keep a fee
Email and password sign-in: buyers and sellers have accounts
Postgres: listings, orders and reviews
Realtime subscriptions (nice to have): messages arrive live
Transactional email: order and message notifications

MVP: about 100 users, $0/mo

Someone with an idea or a solo founder. Built with an AI app builder: describe it and it builds and hosts it.

What	Pick	Monthly
AI coding agent	Base44 Starter	$16
Email	Mailgun Free	$0
Payments	Stripe Standard (US cards)	$43.80
Analytics & errors	PostHog Free	$0

First cost jump: Mailgun: Free limits reached, upgrade to Basic

Open the full MVP plan · Use the MVP stage in Claude

Growth: about 10,000 users, $23.05/mo

A funded team or one with traction. Built with an AI coding agent for each of about 3 developers.

Error tracking: know when something breaks
Daily backups: daily backups once real people depend on it

What	Pick	Monthly
AI coding agent	Augment Code Standard	$20
Hosting	Heroku Basic dyno	$7
Database	Neon Launch	$1.05
Sign-in	Auth0 Free	$0
Email	Amazon SES A la carte	$15
Payments	Stripe Standard (US cards)	$4,380
Analytics & errors	PostHog Pay as you go	$0

First cost jump: Auth0: Free limits reached, upgrade to B2C Essentials

Open the full Growth plan · Use the Growth stage in Claude

Scale: about 100,000 users, $260.64/mo

An established product. Built with an AI coding agent with team billing and admin for about 10 developers.

Error tracking: know when something breaks
Daily backups: daily backups
Point-in-time recovery: restore to any minute after a bad deploy
Multi-factor authentication: two-factor sign-in for accounts worth stealing

What	Pick	Monthly
AI coding agent	Augment Code Standard	$20
Hosting	Fly.io Machine, shared-cpu-1x with 256MB RAM	$62.19
Database	DigitalOcean Managed PostgreSQL Single node (1 vCPU, 1 GiB RAM, 10 GiB disk)	$19.45
Sign-in	WorkOS AuthKit	$0
Email	Amazon SES A la carte	$150
Payments	Stripe Standard (US cards)	$43,800
Analytics & errors	Sentry Team	$29

First cost jump: DigitalOcean Managed PostgreSQL: Single node (1 vCPU, 1 GiB RAM, 10 GiB disk) limits reached, upgrade to Single node (1 vCPU, 2 GiB RAM, 30 GiB disk)

Open the full Scale plan · Use the Scale stage in Claude

What drives the cost

Payment and payout fees on every order
Search and media as listings grow
Messaging volume

Lock-in

Connected seller accounts live with the payment processor; moving them means sellers onboard again.

Use this in Claude (with Kong Reviews connected at https://kongreviews.com/mcp)

What do I use to build this?
And how much will it cost?What do you want to build?

Describe it in a sentence, like “an app that tracks the beans in my pantry”. You get what to build it with, what it runs on, and what it costs now and as it grows, with a source for every price.Describe it and press Plan. You get what to build it with, what it runs on, and what it costs now and as you grow, after the credits you qualify for.

Prices read from each vendor’s own pricing page

Vercel
Supabase
Stripe
Clerk
Resend
Neon
Cloudflare
PostHog

317 services listed across 36 categories. 70 priced in full, plan by plan.

One place
for every stack decision.

Describe it. Get one pick per category, and why.

See where the bill jumps before your users do.

Free tiers, plans and limits, side by side.

Already built? Find what to keep and what to change.

What you actually pay, next to what you planned.

See what real products are built on.

Recordings of the actual app. Inputs are illustrative; Billing shows an example account.

Give your AI assistant
access to Kong Reviews.

It plans the stack, prices it at your scale, and hands back package names, environment variables and docs. Your assistant writes the code.

Then keep going in the same chat. Pick up a saved project, price a change before it is built, track setup step by step, and ask why the bill went up.

Free while in preview.

Claude
ChatGPT
Cursor
VS Code

I’m building a booking app for yoga studios with sign-in, payments and email reminders. What should it run on, and what will it cost at 20,000 users?

Example prompt. The answer is a live result from recommend_stack, the tool your assistant calls, at today’s prices.

No vendor pays to be listed or ranked higher, and there are no referral links.

Every price change is public: who changed what, when and why.

Already built?
Start from what you run.

Point it at your files, repository or website to see what to keep and what to change. Then bring in what you actually pay, next to what you estimated.

Sign-in required for billing and saved stacks.

Spend less time collecting bills

Import a CSV, upload a text-based PDF, paste an invoice or enter an amount. Recurring subscriptions add completed months automatically.

Supported OpenAI, Anthropic, Vercel, Stripe, AWS and DigitalOcean connections sync completed months nightly. Billing access depends on the provider; personal Claude API keys cannot read organization costs.

Forward receipts when they arrive

When receipt forwarding is enabled, send receipts to your private billing address and review the service, month and amount in Billing. It reads the email body, not attachments; upload PDFs separately.

Revisit decisions when things change

Save a stack or audit and enable alerts for price changes, approaching cost jumps, expiring credits and bills above estimates. Checks run daily using saved usage assumptions and require a confirmed email.

Pick what works.
Build what’s next.

Free while in preview. Create a free account to plan, no card needed.

See pricing

Audit Your Stack

Already built? See what your app runs on, what it costs now and as you grow, what it's missing, and what to change.

What's it built on?

Drop files or a project folder package.json, requirements.txt, .env.example, vercel.json, fly.toml, Dockerfile… Only names of services are read; nothing is kept. Choose Files

Or paste a package.json, .env.example or a list of services

Your audit appears here: a grade, what to change first, and what each service costs as you grow.

Plan your stack for free.

Every tool, on this website and in your AI app, is free while Kong Reviews is in preview. There's nothing to buy.

Free

Preview

For founders, product managers and AI coding agents

$0no card needed

Stack recommendations from a PRD or a short description
Cost now, as you grow, and in year one after startup credits
Cost cliffs, and stay, optimise or switch comparisons
70 vendors priced in full, with every plan and what it includes, and more being added
317 developer services on Vendors, 70 priced in full and the rest with free tiers and starting prices, growing as we research more
Audits of apps already built: what they run on, what to change
MCP server with 34 tools for Claude, ChatGPT, Cursor and more
Saved stacks with price re-checks (sign in with email or GitHub)
Share links for any plan

Paid Plans

Not available yet

We may add paid plans later, for things like tracking real bills and team accounts. Nothing is for sale today.

Questions

What is Kong Reviews?

It scopes what you build next, a new product or a feature for the app you already have: which services to use (hosting, database, sign-in, email, payments, analytics and more), how to set them up, and what they will cost now, as you grow and after startup credits. Use it on this website with a free account, or from your AI assistant over MCP each time you plan a feature.

Where do the prices come from?

From each vendor's own pricing page. 70 of the 70 vendors in the cost engine were checked against their pricing pages in October 2026; any others are marked unverified. The other services on Vendors were read in October 2026 for their free tier and lowest paid price; the ones we couldn't read are marked Not Priced Yet. Both keep growing: we add vendors and services as we research them. Every answer lists its sources and the date each price was checked, and a price counts as out of date after 14 days. Check the vendor's page before you commit to anything.

Is it really free?

Yes. Every tool is free during the preview, within fair rate limits. There are no paid plans yet.

Do I need an account?

Yes, a free one, to plan or audit on this website. It also keeps your stacks and sends price alerts. Create it with your email address (we send a 6-digit code, no password) or with GitHub, which asks for no permissions beyond your public profile.

How do I use it from Claude or ChatGPT?

Open Connect AI and pick your app for the setup steps. Then ask in plain language, for example "Here's my PRD, what should I use?"

Do vendors pay to be listed or ranked higher?

No. Rankings come only from fit and cost, and there are no affiliate or referral links. See How we make money.

What happens to the PRD I paste?

It is read on our server with keyword rules to find requirements, then discarded. It is not stored and not sent to an AI provider. See Privacy.

How do I delete my data?

Sign in and go to Settings → Account → Delete account. That removes your account, your saved stacks and every sign-in straight away.

Can you add a vendor?

Yes, and we'll look at adding it.

Still have questions? Email [email protected].

Two-sided marketplace: what to build it with and what it costs

Sample PRD

What it needs

MVP: about 100 users, $0/mo

Growth: about 10,000 users, $23.05/mo

Scale: about 100,000 users, $260.64/mo

What drives the cost

Lock-in

What do I use to build this?And how much will it cost?What do you want to build?

What Are You Building?

Prices read from each vendor’s own pricing page

One placefor every stack decision.

Plan

Cost as you grow

Vendors

Audit

Billing

Showcase

Give your AI assistantaccess to Kong Reviews.

See what real productsare built on.

How services are ranked

See what startups build on.

Already built?Start from what you run.

Pick what works.Build what’s next.

Audit Your Stack

What's it built on?

What it runs on

What matters

Build Library

My Stacks

Billing

Vendors

Missing a Vendor?

Showcase

Built Something?

New startups, daily

Use Kong Reviews from your AI assistant.

Prices, Kept Honest by Everyone

Settings

Admin

Don't miss the next startup.

What an Issue Looks Like

What's in It

Recently Featured

Plan your stack for free.

Free

Paid Plans

Missing a Vendor?

Questions

Pick what works.Build what’s next.

What do I use to build this?
And how much will it cost?What do you want to build?

One place
for every stack decision.

Give your AI assistant
access to Kong Reviews.

See what real products
are built on.

Already built?
Start from what you run.

Pick what works.
Build what’s next.

Pick what works.
Build what’s next.