I Spent 30 Days “Vibe Coding” an MVP — Burned $127, Broke Everything, and Still Found Product-Market

I have recently been diving into the world of vibe coding and I thought of cataloging my experience for the benefit of others. My coding skills are 25 years old (from early 2000s). Even though I did learn “modern” coding for my startup in 2018, I don’t consider myself anything more than a beginner. So when the phenomenon of AI powered coding came up, I had to try it! TL;DR I spent 30 days building a financial planning tool for founders by “vibe coding”. Made every mistake possible. Burned through $127 in Replit credits. Got calculations wrong by 20%. Watched 23 "interested" founders become 2 signups. $127 in Replit credits 20% 23 "interested" founders become 2 signups But I also learned that: (1) AI struggles with precision calculations, (2) founders don't want another spreadsheet—they want advice, and (3) sometimes less is more. One founder offered $50/month for the simplified version. That's validation enough to keep going. $50/month This was a great learning experience for me as I go to be on the other side of the table so to say. I spend time working with founders at accelerators and advising them about getting from zero to 1. This was a good opportunity for me to “eat my own dog food”! Here's the full story and what I'd do differently. Building a Financial Planning Tool for Founders: 3 … Table of Contents The Problem That Obsessed Me Week 1: The Honeymoon Phase (Days 1-7) Day 1: The Dream Begins Days 2-7: Early Mistakes The Magic Incantation Week 2: Reality Check (Days 8-14) Day 8-14: Travel and Trouble Day 15: Existential Dread Day 16: The Credit Crisis The Stack Choices Week 3: User Feedback Changes Everything (Days 15- … Day 17: Time for Feedback Day 18: The Humbling Day 20: Six Hours of Hell Critical Lesson Learned Day 21: The Lightbulb Moment Week 4: The Pivot (Days 22-30) Day 22: Language Regrets Day 23: The "Intuitive" Disaster Day 24: The Harsh Reality of User Acquisition Day 25: The API Awakening Day 26: Precision in Prompts Day 27: Rollback Appreciation Day Day 28: The Hard Truth Day 29: The Best Feedback Day 30: One Founder Who'd Pay The 30-Day Scorecard (Being Brutally Honest) Month 1 Statistics What I Learned About Vibe Coding The Good ✅ The Challenges ⚠️ Key Principles I Discovered 1. Be Surgically Precise with Instructions 2. One Change at a Time 3. Validate Everything 4. Use Rollback Liberally 5. Listen to Users 6. Know When to Pivot If I Started Over Tomorrow What I'd Keep ✅ What I'd Change 🔄 What I'd Skip Entirely ⛔ The One Thing I'd Do Differently What's Next? The Smart Approach: Progressive MVP Phase 1: Validate with Vibe Coding (Current - Week … Phase 2: If It Works, Go Pro (Weeks 9-24) When to Graduate Beyond Vibe Coding If You're Building with Vibe Coding: A Checklist Before You Start While Building When to Pivot Want to Help? Requirements: What You Get: Social Proof (Yes, It's Early, But It's Real) The Mission Building a Financial Planning Tool for Founders: 3 … Table of Contents The Problem That Obsessed Me Week 1: The Honeymoon Phase (Days 1-7) Day 1: The Dream Begins Days 2-7: Early Mistakes The Magic Incantation Week 2: Reality Check (Days 8-14) Day 8-14: Travel and Trouble Day 15: Existential Dread Day 16: The Credit Crisis The Stack Choices Week 3: User Feedback Changes Everything (Days 15- … Day 17: Time for Feedback Day 18: The Humbling Day 20: Six Hours of Hell Critical Lesson Learned Day 21: The Lightbulb Moment Week 4: The Pivot (Days 22-30) Day 22: Language Regrets Day 23: The "Intuitive" Disaster Day 24: The Harsh Reality of User Acquisition Day 25: The API Awakening Day 26: Precision in Prompts Day 27: Rollback Appreciation Day Day 28: The Hard Truth Day 29: The Best Feedback Day 30: One Founder Who'd Pay The 30-Day Scorecard (Being Brutally Honest) Month 1 Statistics What I Learned About Vibe Coding The Good ✅ The Challenges ⚠️ Key Principles I Discovered 1. Be Surgically Precise with Instructions 2. One Change at a Time 3. Validate Everything 4. Use Rollback Liberally 5. Listen to Users 6. Know When to Pivot If I Started Over Tomorrow What I'd Keep ✅ What I'd Change 🔄 What I'd Skip Entirely ⛔ The One Thing I'd Do Differently What's Next? The Smart Approach: Progressive MVP Phase 1: Validate with Vibe Coding (Current - Week … Phase 2: If It Works, Go Pro (Weeks 9-24) When to Graduate Beyond Vibe Coding If You're Building with Vibe Coding: A Checklist Before You Start While Building When to Pivot Want to Help? Requirements: What You Get: Social Proof (Yes, It's Early, But It's Real) The Mission Building a Financial Planning Tool for Founders: 3 … Table of Contents The Problem That Obsessed Me Week 1: The Honeymoon Phase (Days 1-7) Day 1: The Dream Begins Days 2-7: Early Mistakes The Magic Incantation Week 2: Reality Check (Days 8-14) Day 8-14: Travel and Trouble Day 15: Existential Dread Day 16: The Credit Crisis The Stack Choices Week 3: User Feedback Changes Everything (Days 15- … Day 17: Time for Feedback Day 18: The Humbling Day 20: Six Hours of Hell Critical Lesson Learned Day 21: The Lightbulb Moment Week 4: The Pivot (Days 22-30) Day 22: Language Regrets Day 23: The "Intuitive" Disaster Day 24: The Harsh Reality of User Acquisition Day 25: The API Awakening Day 26: Precision in Prompts Day 27: Rollback Appreciation Day Day 28: The Hard Truth Day 29: The Best Feedback Day 30: One Founder Who'd Pay The 30-Day Scorecard (Being Brutally Honest) Month 1 Statistics What I Learned About Vibe Coding The Good ✅ The Challenges ⚠️ Key Principles I Discovered 1. Be Surgically Precise with Instructions 2. One Change at a Time 3. Validate Everything 4. Use Rollback Liberally 5. Listen to Users 6. Know When to Pivot If I Started Over Tomorrow What I'd Keep ✅ What I'd Change 🔄 What I'd Skip Entirely ⛔ The One Thing I'd Do Differently What's Next? The Smart Approach: Progressive MVP Phase 1: Validate with Vibe Coding (Current - Week … Phase 2: If It Works, Go Pro (Weeks 9-24) When to Graduate Beyond Vibe Coding If You're Building with Vibe Coding: A Checklist Before You Start While Building When to Pivot Want to Help? Requirements: What You Get: Social Proof (Yes, It's Early, But It's Real) The Mission Table of Contents Table of Contents The Problem That Obsessed Me The Problem That Obsessed Me Week 1: The Honeymoon Phase (Days 1-7) Day 1: The Dream Begins Days 2-7: Early Mistakes The Magic Incantation Week 1: The Honeymoon Phase (Days 1-7) Day 1: The Dream Begins Days 2-7: Early Mistakes The Magic Incantation Day 1: The Dream Begins Day 1: The Dream Begins Days 2-7: Early Mistakes Days 2-7: Early Mistakes The Magic Incantation The Magic Incantation Week 2: Reality Check (Days 8-14) Day 8-14: Travel and Trouble Day 15: Existential Dread Day 16: The Credit Crisis The Stack Choices Week 2: Reality Check (Days 8-14) Day 8-14: Travel and Trouble Day 15: Existential Dread Day 16: The Credit Crisis The Stack Choices Day 8-14: Travel and Trouble Day 8-14: Travel and Trouble Day 15: Existential Dread Day 15: Existential Dread Day 16: The Credit Crisis Day 16: The Credit Crisis The Stack Choices The Stack Choices Week 3: User Feedback Changes Everything (Days 15- … Day 17: Time for Feedback Day 18: The Humbling Day 20: Six Hours of Hell Critical Lesson Learned Day 21: The Lightbulb Moment Week 3: User Feedback Changes Everything (Days 15- … Day 17: Time for Feedback Day 18: The Humbling Day 20: Six Hours of Hell Critical Lesson Learned Day 21: The Lightbulb Moment Day 17: Time for Feedback Day 17: Time for Feedback Day 18: The Humbling Day 18: The Humbling Day 20: Six Hours of Hell Day 20: Six Hours of Hell Critical Lesson Learned Critical Lesson Learned Day 21: The Lightbulb Moment Day 21: The Lightbulb Moment Week 4: The Pivot (Days 22-30) Day 22: Language Regrets Day 23: The "Intuitive" Disaster Day 24: The Harsh Reality of User Acquisition Day 25: The API Awakening Day 26: Precision in Prompts Day 27: Rollback Appreciation Day Day 28: The Hard Truth Day 29: The Best Feedback Day 30: One Founder Who'd Pay Week 4: The Pivot (Days 22-30) Day 22: Language Regrets Day 23: The "Intuitive" Disaster Day 24: The Harsh Reality of User Acquisition Day 25: The API Awakening Day 26: Precision in Prompts Day 27: Rollback Appreciation Day Day 28: The Hard Truth Day 29: The Best Feedback Day 30: One Founder Who'd Pay Day 22: Language Regrets Day 22: Language Regrets Day 23: The "Intuitive" Disaster Day 23: The "Intuitive" Disaster Day 24: The Harsh Reality of User Acquisition Day 24: The Harsh Reality of User Acquisition Day 25: The API Awakening Day 25: The API Awakening Day 26: Precision in Prompts Day 26: Precision in Prompts Day 27: Rollback Appreciation Day Day 27: Rollback Appreciation Day Day 28: The Hard Truth Day 28: The Hard Truth Day 29: The Best Feedback Day 29: The Best Feedback Day 30: One Founder Who'd Pay Day 30: One Founder Who'd Pay The 30-Day Scorecard (Being Brutally Honest) Month 1 Statistics The 30-Day Scorecard (Being Brutally Honest) Month 1 Statistics Month 1 Statistics Month 1 Statistics What I Learned About Vibe Coding The Good ✅ The Challenges ⚠️ Key Principles I Discovered 1. Be Surgically Precise with Instructions 2. One Change at a Time 3. Validate Everything 4. Use Rollback Liberally 5. Listen to Users 6. Know When to Pivot What I Learned About Vibe Coding The Good ✅ The Challenges ⚠️ Key Principles I Discovered 1. Be Surgically Precise with Instructions 2. One Change at a Time 3. Validate Everything 4. Use Rollback Liberally 5. Listen to Users 6. Know When to Pivot The Good ✅ The Good ✅ The Challenges ⚠️ The Challenges ⚠️ Key Principles I Discovered 1. Be Surgically Precise with Instructions 2. One Change at a Time 3. Validate Everything 4. Use Rollback Liberally 5. Listen to Users 6. Know When to Pivot Key Principles I Discovered 1. Be Surgically Precise with Instructions 2. One Change at a Time 3. Validate Everything 4. Use Rollback Liberally 5. Listen to Users 6. Know When to Pivot 1. Be Surgically Precise with Instructions 1. Be Surgically Precise with Instructions 2. One Change at a Time 2. One Change at a Time 3. Validate Everything 3. Validate Everything 4. Use Rollback Liberally 4. Use Rollback Liberally 5. Listen to Users 5. Listen to Users 6. Know When to Pivot 6. Know When to Pivot If I Started Over Tomorrow What I'd Keep ✅ What I'd Change 🔄 What I'd Skip Entirely ⛔ The One Thing I'd Do Differently If I Started Over Tomorrow What I'd Keep ✅ What I'd Change 🔄 What I'd Skip Entirely ⛔ The One Thing I'd Do Differently What I'd Keep ✅ What I'd Keep ✅ What I'd Change 🔄 What I'd Change 🔄 What I'd Skip Entirely ⛔ What I'd Skip Entirely ⛔ The One Thing I'd Do Differently The One Thing I'd Do Differently What's Next? The Smart Approach: Progressive MVP Phase 1: Validate with Vibe Coding (Current - Week … Phase 2: If It Works, Go Pro (Weeks 9-24) When to Graduate Beyond Vibe Coding What's Next? The Smart Approach: Progressive MVP Phase 1: Validate with Vibe Coding (Current - Week … Phase 2: If It Works, Go Pro (Weeks 9-24) When to Graduate Beyond Vibe Coding The Smart Approach: Progressive MVP The Smart Approach: Progressive MVP Phase 1: Validate with Vibe Coding (Current - Week … Phase 1: Validate with Vibe Coding (Current - Week … Phase 2: If It Works, Go Pro (Weeks 9-24) Phase 2: If It Works, Go Pro (Weeks 9-24) When to Graduate Beyond Vibe Coding When to Graduate Beyond Vibe Coding If You're Building with Vibe Coding: A Checklist Before You Start While Building When to Pivot If You're Building with Vibe Coding: A Checklist Before You Start While Building When to Pivot Before You Start Before You Start While Building While Building When to Pivot When to Pivot Want to Help? Requirements: What You Get: Want to Help? Requirements: What You Get: Requirements: Requirements: What You Get: What You Get: Social Proof (Yes, It's Early, But It's Real) Social Proof (Yes, It's Early, But It's Real) The Mission The Mission Building a Financial Planning Tool for Founders: 30 Days of Vibe Coding A brutally honest journey from idea to MVP, including every mistake, pivot, and lesson learned along the way. A brutally honest journey from idea to MVP, including every mistake, pivot, and lesson learned along the way. Reading time:8 minutesBest for: Founders building with AI, anyone considering vibe coding for serious products Reading time: Best for: The Problem That Obsessed Me The VC leaned forward: "What if your churn drops by 2%?" The VC leaned forward: I watched the founder's face fall. His answer was buried somewhere in a 47-tab Excel model. It would take him 3 hours to calculate. The meeting momentum died right there. I've seen this scene play out dozens of times. Founders spending hours, sometimes days, updating financial models. Breaking formulas. Forgetting which cells to change. Creating circular references that crash Excel. The pain point I kept hearing: The pain point I kept hearing: "I spent 2 days building a financial model for investors. Then they asked 'what if churn drops by 1%?' and I had to rebuild everything." The math is brutal: A large % of startups still use spreadsheets for financial planning and forecasting. Most founders hate every minute of it. A large % of startups still use spreadsheets So I decided to build something better for the founders I mentor at accelerators like Founder Institute, Flat6Labs, Ignite Program, NSRCEL and so on. Week 1: The Honeymoon Phase (Days 1-7) Day 1: The Dream Begins I dove into vibe coding with @Replit, convinced this would be straightforward. The AI influencers made it look easy on TikTok, right? My initial vision: My initial vision: AI-assisted financial cockpit ✨ Real-time data sync with QuickBooks, Stripe 📊 Scenario planning built-in 🎯 Investor-ready exports in seconds 📄 AI-assisted financial cockpit ✨ Real-time data sync with QuickBooks, Stripe 📊 Scenario planning built-in 🎯 Investor-ready exports in seconds 📄 Estimated timeline: 2-3 weeks to MVP Estimated timeline: [Narrator voice: It was not 2-3 weeks] [Narrator voice: It was not 2-3 weeks] Days 2-7: Early Mistakes Reality check came fast. I made three critical early mistakes: Mistake #1: Assumed the AI agent operates in parallel Mistake #1: Assumed the AI agent operates in parallel I gave multiple instructions by Replit Agent while it was working on my previous prompt: "Make the dashboard cleaner" "Add a night mode" "Fix the calculation bug" "Make the dashboard cleaner" "Add a night mode" "Fix the calculation bug" The agent stopped, absorbed all the prompts, got confused, and created a Frankenstein version that did none of them well. Cost: 6 rollbacks, 3 hours lost, $23 in credits Cost: Mistake #2: Underestimated UI complexity Mistake #2: Underestimated UI complexity Me: "Add night mode"AI:Proceeds to make 47 changesResult: White text on white background, buttons invisible, complete disaster Proceeds to make 47 changes Patiently working through font/background mismatches took 3 days longer than expected. 3 days Mistake #3: Wasn't precise with instructions Mistake #3: Wasn't precise with instructions Bad prompt:"Make it more intuitive"What happened: AI changed the entire navigation structure Bad prompt: What happened: Better prompt:"Change the 'Calculate' button color to blue (#0066CC) and increase font size to 16px"What happened: Exactly what I wanted Better prompt: What happened: The Magic Incantation I discovered the key phrase for vibe coding for use with all vibe coding tools: "Don't make any changes without confirming your understanding with me." "Don't make any changes without confirming your understanding with me." This simple instruction could have saved me $50+ in wasted iterations. $50+ in wasted iterations Week 2: Reality Check (Days 8-14) Day 8-14: Travel and Trouble Summer travel (to Japan), slowed me down, but also gave me perspective on what wasn't working. Things I learned while vibe coding from airport lounges: Hotel WiFi + Replit = frustration TypeScript errors are harder to debug on mobile The rollback button becomes your best friend Hotel WiFi + Replit = frustration TypeScript errors are harder to debug on mobile The rollback button becomes your best friend I would recommend Replit as your starting point for Vibe coding if you do not know much about coding and deploying applications. Replit handles all that easily. Also it takes care of protecting your API keys and SECRETS which means no data leaks and high cloud or AI bills! Plus it has a dedicated AI agent that you can chat with, understand code, review code and plan your work BEFORE you build. All of which I found quite useful. Day 15: Existential Dread Tuesday, 3:47 PM:Recurring error to render the screenTuesday, 4:15 PM:Still debuggingTuesday, 6:30 PM:Finally understand it's a TypeScript type issueTuesday, 11:45 PM: Still broken Tuesday, 3:47 PM: Tuesday, 4:15 PM: Tuesday, 6:30 PM: Tuesday, 11:45 PM: Took a whole day just to understand the code. whole day Should I have told the agent to use Python (a language I somewhat understand). Too late. The AI Agent was coding away in TypeScript. A language I don't really know. Thank god for @Replit's rollback options. Thank god for @Replit's rollback options. Day 16: The Credit Crisis Lesson learned: Replit credits run out FAST. Lesson learned: My spending pattern: Week 1: $34 in credits Week 2: $93 in credits (yikes!) Week 1: $34 in credits Week 2: $93 in credits (yikes!) I was iterating rapidly, making changes, rolling back, trying again. Each iteration can cost $2-5 depending on complexity. New rule: Budget $40/week maximum. If I hit the limit, stop and reflect on why I'm burning through credits. This is where the limit feature in Replit comes in handy. New rule: The Stack Choices I integrated: @Brevo for system emails (free tier = win). Basically to send emails to users. @MistralAI for the built-in AI advisor (seemed cheap at first...). I assumed that Open AI API calls would be too expensive. @Brevo for system emails (free tier = win). Basically to send emails to users. @Brevo @MistralAI for the built-in AI advisor (seemed cheap at first...). I assumed that Open AI API calls would be too expensive. @MistralAI Both seemed reasonable. The MistralAI choice would come back to haunt me. Week 3: User Feedback Changes Everything (Days 15-21) Day 17: Time for Feedback After clearing up errors while traveling, I started hunting for testers. Posted in 3 founder Slack channels: "Building a financial planning tool that doesn't suck. Need critical feedback. DM if interested." Response: crickets 🦗 crickets Day 18: The Humbling Finally got 1 friend and 2 founders to try the MVP. 1 friend 2 founders The feedback was... brutal: Issue #1: Financial calculations were off by 20% Issue #1: Financial calculations were off by 20% A founder's CAC calculation showed $47 when it should have been $58.75. $47 $58.75 That 20% error could have cost them their Series A round. Why it happened: I had MistralAI calculate it based on vague instructions. The AI made assumptions about what "customer acquisition cost" meant. Why it happened: Issue #2: Export feature crashed on larger models Issue #2: Export feature crashed on larger models Any model with >50 rows of data caused a memory overflow. Issue #3: "Too many clicks to get to runway calculation" Issue #3: "Too many clicks to get to runway calculation" The thing founders wanted most (runway) was buried 3 screens deep. This was definitely harder than the AI influencers make it seem! Day 20: Six Hours of Hell The bug: LTV/CAC calculations were consistently wrong. The bug: Time spent: 6 hours straight debugging Time spent: The cause: @MistralAI was interpreting "monthly churn" as "annual churn" in some scenarios, and "annual churn" as "monthly churn" in others. The cause: When I asked it to "calculate customer lifetime value," it made assumptions: Sometimes it used monthly churn rate Sometimes it used annual churn rate Sometimes it invented its own churn calculation Sometimes it used monthly churn rate Sometimes it used annual churn rate Sometimes it invented its own churn calculation The fix: Be surgically precise with financial formulas. The fix: Bad prompt: Bad prompt: Calculate LTV Calculate LTV Good prompt: Good prompt: Calculate LTV as: (Average Revenue Per User * Gross Margin) / Monthly Churn Rate where: - Average Revenue Per User = Total MRR / Active Customers - Gross Margin = (Revenue - COGS) / Revenue - Monthly Churn Rate = Churned Customers This Month / Active Customers Start of Month Calculate LTV as: (Average Revenue Per User * Gross Margin) / Monthly Churn Rate where: - Average Revenue Per User = Total MRR / Active Customers - Gross Margin = (Revenue - COGS) / Revenue - Monthly Churn Rate = Churned Customers This Month / Active Customers Start of Month Critical Lesson Learned Always validate AI outputs with manual calculations first. Always validate AI outputs with manual calculations first. I started keeping a spreadsheet (yes, ironic) to validate every calculation the AI generated. Day 21: The Lightbulb Moment One founder cut through all the complexity: "I don't want another financial model builder. I just want to ask 'how do I extend runway by 3 months?' and get an answer." So simple. So obvious. I started pivoting immediately. Natural language queries → instant financial insights. This changed everything. This is where I added a detailed chat functionality for the founders to ask questions about their financial model based on what they had entered so far. Week 4: The Pivot (Days 22-30) Day 22: Language Regrets Regret of the month: Starting with TypeScript instead of Python. Regret of the month: When financial formulas get complex, I spent more time debugging syntax than building features. Example that took 2 hours to fix: // What I wanted: const runway = currentCash / monthlyBurn; // What TypeScript gave me: Type 'number | undefined' is not assignable to type 'number' // What I wanted: const runway = currentCash / monthlyBurn; // What TypeScript gave me: Type 'number | undefined' is not assignable to type 'number' Note to future self: Pick programming languages you actually understand for serious projects! Note to future self: Day 23: The "Intuitive" Disaster Replit credits burned through again. $11 in one afternoon. $11 in one afternoon. I built a "scenario comparison" feature that took 47 iterations because I kept saying "make it more intuitive" without being specific. 47 iterations Iteration 1:"Make it more intuitive"AI changes the entire layout Iteration 1: AI changes the entire layout Iteration 2:"No, not like that, more intuitive"AI changes the color scheme Iteration 2: AI changes the color scheme Iteration 3:"JUST MAKE IT INTUITIVE"AI adds tooltips everywhere Iteration 3: AI adds tooltips everywhere ...45 iterations later... ...45 iterations later... New rule: Define "intuitive" BEFORE asking for changes. New rule: Better approach: "Intuitive means: (1) Show both scenarios side-by-side, (2) Highlight differences in yellow, (3) Add a 'Switch to This Scenario' button on the right" Day 24: The Harsh Reality of User Acquisition Posted on 5 founder Slack groups asking for testers: 5 founder Slack groups Results: Results: 23 "looks interesting!" 😊 2 actual signups 😐 0 completed onboarding 😭 23 "looks interesting!" 😊 2 actual signups 😐 0 completed onboarding 😭 Conversion funnel: Conversion funnel: Interest: 23 Signup: 2 (8.7%) Onboarding completion: 0 (0%) Interest: 23 Signup: 2 (8.7%) Onboarding completion: 0 (0%) Making stuff people want ≠ Making stuff people actually use. Day 25: The API Awakening Founders kept asking: "Can it sync with QuickBooks?" Me: "Sure, how hard can API integration be?" Me: [Researches QuickBooks API for 3 hours] [Researches QuickBooks API for 3 hours] What's required: What's required: OAuth 2.0 flow setup Webhook validation Data mapping between QuickBooks and my schema Error handling for rate limits Token refresh logic Accounting rules validation OAuth 2.0 flow setup Webhook validation Data mapping between QuickBooks and my schema Error handling for rate limits Token refresh logic Accounting rules validation Realization: This isn't happening in vibe coding. Not anytime soon. Realization: Day 26: Precision in Prompts @MistralAI is great, but I learned you need VERY specific prompts for financial calculations. VERY specific prompts Bad prompt: Bad prompt: Calculate runway Calculate runway What AI does: Makes assumptions, might use wrong numbers What AI does: Good prompt: Good prompt: Calculate runway as: current_cash / monthly_burn_rate where monthly_burn_rate = (total_expenses - revenue) / months Use these exact values: - current_cash: $250,000 - total_expenses (last 3 months): $180,000 - revenue (last 3 months): $45,000 - months: 3 Show your work step by step. Calculate runway as: current_cash / monthly_burn_rate where monthly_burn_rate = (total_expenses - revenue) / months Use these exact values: - current_cash: $250,000 - total_expenses (last 3 months): $180,000 - revenue (last 3 months): $45,000 - months: 3 Show your work step by step. What AI does: Gets it right every time What AI does: Precision matters in finance. No room for ambiguity. Day 27: Rollback Appreciation Day Used @Replit's rollback feature 12 times in one day. 12 times What happened: I tried to add "smart defaults" for SaaS metrics (based on industry benchmarks). What happened: Instead, I broke: The calculation engine The export functionality The scenario comparison User authentication (somehow?) The calculation engine The export functionality The scenario comparison User authentication (somehow?) Time to fix manually:Unknown, gave up after 1 hourTime to rollback: 30 seconds Time to fix manually: Time to rollback: Sometimes the best code is the code you don't write. Day 28: The Hard Truth After 4 weeks, I admitted what I'd been avoiding: The full vision is too complex for vibe coding. The full vision is too complex for vibe coding. I scaled back to core MVP: ✅ Manual financial model builder ✅ AI advisor for benchmarks ✅ Basic scenario planning (3 scenarios max) ❌ Real-time integrations (later) ❌ Advanced version control (later) ❌ Multi-user collaboration (later) ✅ Manual financial model builder ✅ AI advisor for benchmarks ✅ Basic scenario planning (3 scenarios max) ❌ Real-time integrations (later) ❌ Advanced version control (later) ❌ Multi-user collaboration (later) Sometimes less is more. Day 29: The Best Feedback One founder's comment changed my entire approach: "I don't need another spreadsheet. I need someone to tell me if my numbers make sense." Tool → Advisor. This was the pivot. Not another financial model builder. An AI-powered financial advisor that: Validates assumptions Flags unrealistic numbers Suggests improvements Answers "what if" questions Validates assumptions Flags unrealistic numbers Suggests improvements Answers "what if" questions Sometimes users tell you exactly what to build if you listen carefully enough. Day 30: One Founder Who'd Pay Posted the scaled-back version. Got brutal but helpful feedback. Then one founder said: "This is the first time I've understood my unit economics without a finance degree. I'd pay $50/month for this." That's validation enough to keep going. That's validation enough to keep going. The 30-Day Scorecard (Being Brutally Honest) Month 1 Statistics Development: Development: Days coding: 30 Replit credits spent: $127 Lines of code written: ~3,500 (mostly by AI) Rollbacks executed: 73 Languages learned the hard way: 1 (TypeScript) Days coding: 30 Days coding: Replit credits spent: $127 Replit credits spent: Lines of code written: ~3,500 (mostly by AI) Lines of code written: Rollbacks executed: 73 Rollbacks executed: Languages learned the hard way: 1 (TypeScript) Languages learned the hard way: User Metrics: User Metrics: Interested parties: 23 Actual signups: 12 Completed onboarding: 3 Completed models: 3 Would pay: 1 Revenue: $0 Interested parties: 23 Interested parties: Actual signups: 12 Actual signups: Completed onboarding: 3 Completed onboarding: Completed models: 3 Completed models: Would pay: 1 Would pay: Revenue: $0 Revenue: Key Wins: Key Wins: 🎯 Found product-market fit signal (1 founder willing to pay) 🎯 Validated core problem (founders hate Excel) 🎯 Discovered simpler solution (advisor > tool) 🎯 Found product-market fit signal (1 founder willing to pay) 🎯 Validated core problem (founders hate Excel) 🎯 Discovered simpler solution (advisor > tool) Key Losses: Key Losses: ❌ Built too much complexity first ❌ Didn't validate calculations carefully enough ❌ Chose wrong programming language ❌ Wasted $50+ on vague prompts ❌ Built too much complexity first ❌ Didn't validate calculations carefully enough ❌ Chose wrong programming language ❌ Wasted $50+ on vague prompts What I Learned About Vibe Coding The Good ✅ Rapid prototyping: Went from idea to testable MVP in 2 weeks Low initial investment: $127 total vs. $20K+ for developers Quick iterations: Try, fail, rollback, try again in minutes AI assistance: Great for boilerplate and standard patterns No hiring headaches: No interviews, no management, no equity Rapid prototyping: Went from idea to testable MVP in 2 weeks Rapid prototyping: Low initial investment: $127 total vs. $20K+ for developers Low initial investment: Quick iterations: Try, fail, rollback, try again in minutes Quick iterations: AI assistance: Great for boilerplate and standard patterns AI assistance: No hiring headaches: No interviews, no management, no equity No hiring headaches: The Challenges ⚠️ Credit management: Can get expensive fast with too many iterations Complex calculations: AI struggles with precision in financial formulas Integration limitations: Enterprise APIs need proper development Language constraints: Stick with what you know or pay the learning tax Precision required: Vague instructions = wasted time and credits Debugging difficulty: Understanding AI-generated code is hard Credit management: Can get expensive fast with too many iterations Credit management: Complex calculations: AI struggles with precision in financial formulas Complex calculations: Integration limitations: Enterprise APIs need proper development Integration limitations: Language constraints: Stick with what you know or pay the learning tax Language constraints: Precision required: Vague instructions = wasted time and credits Precision required: Debugging difficulty: Understanding AI-generated code is hard Debugging difficulty: Key Principles I Discovered 1. Be Surgically Precise with Instructions Don't say:"Make it better"Do say: "Change button color to #0066CC, increase font size to 16px, add 8px padding" Don't say: Do say: 2. One Change at a Time Never give the AI multiple tasks in parallel. Wait for completion, review, then proceed. Bad workflow: Bad workflow: "Add dark mode" "Fix the bug" "Improve performance" "Add dark mode" "Fix the bug" "Improve performance" Good workflow: Good workflow: "Add dark mode" [Wait for completion] [Review changes] "Now fix the calculation bug in line 47" "Add dark mode" [Wait for completion] [Review changes] "Now fix the calculation bug in line 47" 3. Validate Everything Especially financial calculations. Don't trust the AI. Check manually. 4. Use Rollback Liberally It's there for a reason. I rolled back 73 times in 30 days. No shame. 73 times 5. Listen to Users They'll tell you what to build. The founder who said "I need someone to tell me if my numbers make sense" gave me the entire product direction. 6. Know When to Pivot Not everything can be vibe coded. Enterprise integrations, complex calculations, and performance-critical features need traditional development. If I Started Over Tomorrow What I'd Keep ✅ Vibe coding for rapid prototyping: Still the fastest way to test ideas Brutal honesty in user testing: Critical feedback > polite feedback The pivot to "advisor not tool": This is the winning insight Daily build-in-public updates: Accountability + audience building Vibe coding for rapid prototyping: Still the fastest way to test ideas Vibe coding for rapid prototyping: Brutal honesty in user testing: Critical feedback > polite feedback Brutal honesty in user testing: The pivot to "advisor not tool": This is the winning insight The pivot to "advisor not tool": Daily build-in-public updates: Accountability + audience building Daily build-in-public updates: What I'd Change 🔄 Start with Python, not TypeScript Language I understand Better for data/calculations Easier to debug Get 10 user interviews BEFORE building Would have discovered the "advisor not tool" insight on Day 1 Could have skipped 2 weeks of wrong direction. Funnily enough I take a class on “Customer Validation” at an accelerator. But did not follow my own advice! Set a 2-week deadline for MVP v1 Prevents feature creep Forces prioritization Builds shipping muscle Budget $200 for Replit, hard stop If I exceed budget, something's wrong Forces better prompt engineering Prevents death by 1000 iterations Build manual process first, automate second Would have discovered QuickBooks integration isn't MVP Could have launched 2 weeks earlier Start with Python, not TypeScript Language I understand Better for data/calculations Easier to debug Start with Python, not TypeScript Language I understand Better for data/calculations Easier to debug Language I understand Better for data/calculations Easier to debug Get 10 user interviews BEFORE building Would have discovered the "advisor not tool" insight on Day 1 Could have skipped 2 weeks of wrong direction. Funnily enough I take a class on “Customer Validation” at an accelerator. But did not follow my own advice! Get 10 user interviews BEFORE building Would have discovered the "advisor not tool" insight on Day 1 Could have skipped 2 weeks of wrong direction. Funnily enough I take a class on “Customer Validation” at an accelerator. But did not follow my own advice! Would have discovered the "advisor not tool" insight on Day 1 Could have skipped 2 weeks of wrong direction. Funnily enough I take a class on “Customer Validation” at an accelerator. But did not follow my own advice! Set a 2-week deadline for MVP v1 Prevents feature creep Forces prioritization Builds shipping muscle Set a 2-week deadline for MVP v1 Prevents feature creep Forces prioritization Builds shipping muscle Prevents feature creep Forces prioritization Builds shipping muscle Budget $200 for Replit, hard stop If I exceed budget, something's wrong Forces better prompt engineering Prevents death by 1000 iterations Budget $200 for Replit, hard stop If I exceed budget, something's wrong Forces better prompt engineering Prevents death by 1000 iterations If I exceed budget, something's wrong Forces better prompt engineering Prevents death by 1000 iterations Build manual process first, automate second Would have discovered QuickBooks integration isn't MVP Could have launched 2 weeks earlier Build manual process first, automate second Would have discovered QuickBooks integration isn't MVP Could have launched 2 weeks earlier Would have discovered QuickBooks integration isn't MVP Could have launched 2 weeks earlier What I'd Skip Entirely ⛔ Night mode - Nobody asked for it, took 3 days Perfect UI - Founders want function over form Integration promises - Validate manual flow first Advanced features - Get 10 paying users before adding more Night mode - Nobody asked for it, took 3 days Night mode Perfect UI - Founders want function over form Perfect UI Integration promises - Validate manual flow first Integration promises Advanced features - Get 10 paying users before adding more Advanced features The One Thing I'd Do Differently Talk to 50 founders BEFORE writing a single line of code. Talk to 50 founders BEFORE writing a single line of code. Not 5. Not 10. Fifty. Fifty. Ask them: Show me your current financial model What takes the longest to update? What question do investors always ask? What would you pay for a solution? Show me your current financial model What takes the longest to update? What question do investors always ask? What would you pay for a solution? This would have saved me 2 weeks and $$ in wasted effort. What's Next? The Smart Approach: Progressive MVP I'm not building everything at once anymore. Here's the realistic path: Phase 1: Validate with Vibe Coding (Current - Weeks 5-8) Build: Build: ✅ Manual financial model builder ✅ AI advisor for validating assumptions ✅ Basic scenario planning (3 scenarios) ✅ Export to Excel/PDF ✅ Natural language Q&A ✅ Manual financial model builder ✅ AI advisor for validating assumptions ✅ Basic scenario planning (3 scenarios) ✅ Export to Excel/PDF ✅ Natural language Q&A Goal: Get to 10 paying customers at $50/month Goal: What I'm trying to prove: What I'm trying to prove: Core value proposition works Users prefer this vs. spreadsheets AI advisor adds real value Basic unit economics engine is sufficient Core value proposition works Users prefer this vs. spreadsheets AI advisor adds real value Basic unit economics engine is sufficient Success criteria: Success criteria: 10 paid subscribers 40 At least 5 would "very disappointed" if product went away 10 paid subscribers 40 At least 5 would "very disappointed" if product went away Phase 2: If It Works, Go Pro (Weeks 9-24) After 50-100 paying founders, consider: After 50-100 paying founders, consider: Hiring fintech-experienced developers Building real-time integrations Adding enterprise security (SOC 2) Scaling infrastructure Hiring fintech-experienced developers Building real-time integrations Adding enterprise security (SOC 2) Scaling infrastructure Budget: $50K-100K (bootstrap or small angel round) Budget: When to Graduate Beyond Vibe Coding Vibe coding is great for: Vibe coding is great for: ✅ Rapid prototyping ✅ Basic CRUD operations ✅ AI integration (OpenAI/Mistral API calls) ✅ Export functionality ✅ User feedback and fast iteration ✅ Landing pages and marketing sites ✅ Rapid prototyping ✅ Basic CRUD operations ✅ AI integration (OpenAI/Mistral API calls) ✅ Export functionality ✅ User feedback and fast iteration ✅ Landing pages and marketing sites Where you'll hit walls: Where you'll hit walls: ❌ Complex financial formulas (cohort retention curves, NPV calculations) ❌ Enterprise API integrations (OAuth flows, webhook handling) ❌ Background jobs for data sync ❌ Multi-tenant security architecture ❌ Performance optimization (sub-300ms queries) ❌ Real-time collaboration features ❌ Complex financial formulas (cohort retention curves, NPV calculations) ❌ Enterprise API integrations (OAuth flows, webhook handling) ❌ Background jobs for data sync ❌ Multi-tenant security architecture ❌ Performance optimization (sub-300ms queries) ❌ Real-time collaboration features The graduation threshold: When you have 10+ paying customers asking for features that vibe coding can't deliver. The graduation threshold: If You're Building with Vibe Coding: A Checklist Save yourself time and money. Use this: Before You Start [ ] Choose a language you actually understand [ ] Set a credit budget ($X per week max) [ ] Define "done" for your MVP (write it down) [ ] Find 3 users who will test, not just say "sounds interesting" [ ] Interview 10+ potential users first [ ] Write down the #1 problem you're solving [ ] Choose a language you actually understand [ ] Set a credit budget ($X per week max) [ ] Define "done" for your MVP (write it down) [ ] Find 3 users who will test, not just say "sounds interesting" [ ] Interview 10+ potential users first [ ] Write down the #1 problem you're solving While Building [ ] One prompt at a time, wait for completion [ ] Define vague words ("intuitive", "clean", "simple") [ ] Validate ALL calculations manually [ ] Use rollback guilt-free [ ] Track credit spend daily [ ] Screenshot working versions before major changes [ ] One prompt at a time, wait for completion [ ] Define vague words ("intuitive", "clean", "simple") [ ] Validate ALL calculations manually [ ] Use rollback guilt-free [ ] Track credit spend daily [ ] Screenshot working versions before major changes When to Pivot [ ] If the same error persists after 5 attempts [ ] If you're explaining more than building [ ] If test users can't complete core flow [ ] If enterprise features keep coming up [ ] If you've spent >$200 without paying users [ ] If the same error persists after 5 attempts [ ] If you're explaining more than building [ ] If test users can't complete core flow [ ] If enterprise features keep coming up [ ] If you've spent >$200 without paying users Want to Help? I'm looking for 10 founders to: 10 founders Test the MVP for 1 week Jump on a 15-min feedback call Get free lifetime access if you help shape v1 Test the MVP for 1 week Jump on a 15-min feedback call Get free lifetime access if you help shape v1 Requirements: ✅ Pre-seed to Series A stage ✅ Currently use Excel/Sheets for financial planning ✅ Willing to be brutally honest (critical feedback only) ✅ Can commit to testing for 1 week ✅ Pre-seed to Series A stage ✅ Currently use Excel/Sheets for financial planning ✅ Willing to be brutally honest (critical feedback only) ✅ Can commit to testing for 1 week What You Get: 🎁 Free lifetime access (worth $600/year) 🎁 Priority feature requests 🎁 Direct access to me via WhatsApp 🎁 Your logo on the "Built with Founders" page 🎁 Free lifetime access (worth $600/year) 🎁 Priority feature requests 🎁 Direct access to me via WhatsApp 🎁 Your logo on the "Built with Founders" page Spots available: 7/10 (3 already filled) as of Nov 1, 2025 Spots available: How to apply: DM me on Twitter @RenjitPhilip. Want to test out what I built? Here is the link» https://runwayai.futureu.co How to apply: @RenjitPhilip @RenjitPhilip https://runwayai.futureu.co https://runwayai.futureu.co Social Proof (Yes, It's Early, But It's Real) "This is the first time I've understood my unit economics without a finance degree. I'd pay $50/month for this."— Mike R., SaaS Founder, Pre-seed — Mike R., SaaS Founder, Pre-seed "You answered my investor question in 30 seconds. It would have taken me 3 hours in Excel."— Sarah K., Marketplace Founder, Seed — Sarah K., Marketplace Founder, Seed The Mission Kill the 47-tab Excel financial model. Kill the 47-tab Excel financial model. Every founder deserves: ✅ Real-time financial dashboards ✅ AI that explains the numbers ✅ Scenario planning in seconds ✅ Investor-ready exports instantly ✅ Real-time financial dashboards ✅ AI that explains the numbers ✅ Scenario planning in seconds ✅ Investor-ready exports instantly The journey continues. Day 31 starts tomorrow. Follow along: @RenjitPhilip #vibecoding #BuildInPublic Follow along: @RenjitPhilip #vibecoding #BuildInPublic @RenjitPhilip P.S. - If you found this helpful, share it with a founder friend who's drowning in Excel. They'll thank you later. Here is the link» https://runwayai.futureu.co P.S. https://runwayai.futureu.co https://runwayai.futureu.co