Launch Ready for marketplace products: The API security Founder Playbook for a founder who built in Cursor and needs production hardening.

Launch Ready for marketplace products: The API security Founder Playbook for a founder who built in Cursor and needs production hardening

You built the marketplace in Cursor, the core flows work, and now the dangerous part starts: real users, real payments, real data, and real failure modes.

The usual problem is not "the app does not exist." It is that the app can be reached, abused, scraped, misrouted, or taken down before it has a chance to convert. If you ignore that, the business cost is ugly: broken onboarding, failed email delivery, bad SEO from missing redirects, support tickets from domain confusion, app downtime during launch, and exposed customer data if secrets or auth are handled badly.

What This Sprint Actually Fixes

Launch Ready is my 48-hour production hardening sprint for founders who built a marketplace product in Cursor and need the public-facing stack made safe enough to launch.

I focus on the boring but expensive parts that usually get skipped during AI-built development:

• Domain setup and DNS
• Redirects and subdomains
• Cloudflare configuration
• SSL setup
• Caching and basic performance protection
• DDoS protection
• SPF, DKIM, and DMARC for email deliverability
• Production deployment checks
• Environment variables and secrets handling
• Uptime monitoring
• Handover checklist

For marketplace products, this matters more than most founders realize. You are not just shipping a landing page. You are shipping trust between buyers and sellers, so one broken checkout route or one leaked API key can damage both sides of the marketplace at once.

If you want me to look at your current stack before you commit to anything, book a discovery call at https://cal.com/cyprian-aarons/discovery.

The Production Risks I Look For

I do not start with design tweaks. I start with failure points that can cost revenue or create a security incident.

| Risk | What I check | Business impact | | --- | --- | --- | | Broken auth on API routes | Missing session checks, weak token validation, role bypasses | Unauthorized access to user accounts or listings | | Overexposed endpoints | Public routes that should be private, weak CORS rules | Data scraping, abuse, higher infra costs | | Secret leakage | Keys in Cursor output, env files in repo history, client-side leaks | Account takeover, billing abuse, vendor lockout | | Bad rate limiting | No throttling on login, search, signup, or messaging APIs | Bot abuse, spam sellers/buyers, downtime | | Weak input validation | Untrusted payloads in create/update endpoints | Injection bugs, corrupted listings, failed orders | | Missing observability | No logs for auth failures or webhook errors | Slow incident response and longer outages | | Poor email authentication | SPF/DKIM/DMARC not configured correctly | Emails land in spam or get spoofed |

For marketplace products built in Cursor or similar tools like Lovable or v0, I also look for AI-generated shortcuts that create hidden risk:

• Prompt-injected admin tools that trust user content too much.
• Webhook handlers that accept any payload without signature verification.
• Server actions that assume frontend validation is enough.
• Public storage buckets attached to user uploads.
• Search or recommendation endpoints with no abuse controls.
• Admin-only routes exposed through predictable URLs.

If there is any AI-assisted moderation or seller onboarding flow, I test for prompt injection and unsafe tool use. A marketplace is a good place for attackers to hide malicious instructions inside product descriptions, support messages, or uploaded content.

The Sprint Plan

Here is how I usually run this sprint.

Day 1: Audit and stabilize

I start by mapping the live path from domain to app to backend. That means checking DNS records, hosting config, environment variables, Cloudflare settings if present, and every public endpoint tied to the marketplace.

Then I review:

• Auth flows for buyers and sellers
• Admin access paths
• Webhooks from Stripe or other payment tools
• Email sending setup
• File upload paths
• Any API route exposed by the frontend

I also check whether your current deployment can survive first traffic. If your app is on Vercel, Netlify, Firebase Hosting, Supabase Edge Functions, Render, Railway, or a similar stack used after building in Cursor or Bolt-like tools, I verify the deployment settings instead of assuming they are correct.

Day 2: Hardening and handover

I lock down the production surface area.

That usually includes:

• Setting proper redirects so old URLs do not break SEO or user flow
• Enabling SSL everywhere
• Applying Cloudflare protections where appropriate
• Setting caching rules for static assets and safe pages
• Verifying SPF/DKIM/DMARC so transactional email does not fail silently
• Moving secrets into environment variables correctly
• Rotating exposed keys if needed
• Adding uptime monitoring on homepage plus critical API routes
• Writing a handover checklist so you know what was changed

If there is time-sensitive risk like an exposed key or an open admin route issue with active traffic potential p95 latency spikes above 800 ms under load then I treat that as launch-blocking and fix it first.

What You Get at Handover

You should leave this sprint with assets you can actually use.

Deliverables include:

• Domain connected correctly with clean DNS records
• SSL live across all relevant subdomains
• Cloudflare configured for protection and caching where it makes sense
• Redirect map for primary URLs and legacy paths
• SPF/DKIM/DMARC records verified where mail is part of your product flow
• Production deployment validated against the live environment
• Secrets moved out of unsafe places and documented properly
• Uptime monitoring set up for core pages or APIs
• A handover checklist with next steps and known limits
• Notes on any remaining risks I found but did not change because they need product decisions

I also give you practical guidance on what to watch after launch. For example: if your checkout conversion drops below target after deployment because of redirect mistakes or email deliverability issues then we catch that early instead of learning about it from lost revenue.

If your marketplace uses AI features such as automated listing summaries or seller support replies I will note where red-team testing should continue after handover. That includes prompt injection tests using malicious listing text and jailbreak attempts against any internal assistant workflow.

When You Should Not Buy This

Do not buy Launch Ready if you are still changing core product logic every few hours. If your marketplace model is unstable then production hardening will just force rework later.

This sprint is also not right if:

• You have no deployable build yet.
• Your backend architecture is still being rewritten.
• You need full feature development rather than launch safety.
• Your team expects me to own ongoing engineering after handover without a separate scope.
• You have legal/compliance questions that need counsel rather than engineering judgment.

The DIY alternative is simple: freeze feature work for 24 hours and do a minimum viable hardening pass yourself. Check DNS records at your registrar and host. Turn on SSL. Verify email authentication. Move secrets into env vars. Add basic uptime alerts. Review every public API route for auth checks and rate limits. If you can do all of that confidently without breaking launch timing then you may not need me yet.

Founder Decision Checklist

Answer these yes/no questions before you launch:

1. Is your custom domain pointing to the correct production app? 2. Do all major pages redirect cleanly from old URLs? 3. Is SSL active on every public subdomain? 4. Are SPF/DKIM/DMARC set up so emails reach inboxes? 5. Are production secrets stored outside source control? 6. Do login signup checkout messaging or webhook endpoints have auth checks? 7. Have you limited repeated requests with rate limiting? 8. Can you see uptime alerts if the site goes down? 9. Have you tested buyer seller admin flows on mobile? 10. Would losing access to one API key today stop your launch?

If you answered "no" to two or more of those questions then Launch Ready will probably save you time.

References

1. roadmap.sh API Security Best Practices - https://roadmap.sh/api-security-best-practices 2. OWASP API Security Top 10 - https://owasp.org/www-project-api-security/ 3. Cloudflare SSL/TLS documentation - https://developers.cloudflare.com/ssl/ 4. Google Email sender guidelines - https://support.google.com/a/answer/81126 5. RFC 7489 DMARC - https://www.rfc-editor.org/rfc/rfc7489

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Take the next step

If this is a problem in your product right now, here is what to do next:

• [Use the free Cyprian tools](/tools) - estimate cost, score app risk, check launch readiness, or pick the right service sprint.

• [Book a discovery call](/contact) - I will tell you honestly whether you need a sprint or if you can DIY the next step.

*Written by Cyprian Tinashe Aarons - senior full-stack and AI engineer helping founders rescue, launch, automate, and scale AI-built products.*