Eu passei 30 dias “codificando Vibe” um MVP – queimou US $ 127, quebrou tudo e ainda encontrou o mercado de produtos

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 . Got calculations wrong by . Watched . $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 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”! Aqui está a história completa e o que eu faria diferente. 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: 30 Days of Vibe Coding A brutally honest journey from idea to MVP, including every mistake, pivot, and lesson learned along the way. 8 minutes Founders building with AI, anyone considering vibe coding for serious products Reading time: Best for: The Problem That Obsessed Me "What if your churn drops by 2%?" The VC leaned forward: Eu vi o rosto do fundador cair. Sua resposta foi enterrada em algum lugar em um modelo do Excel de 47 tabulas. Levaria 3 horas para calcular. 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: "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." A matemática é brutal: 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: Cockpit financeiro assistido Sincronização de dados em tempo real com QuickBooks, Stripe Scenario planning built-in 🎯 Investor-ready exports in seconds 📄 2-3 weeks to MVP Estimated timeline: [Votação do narrador: Não foi 2-3 semanas] Days 2-7: Early Mistakes A verificação da realidade veio rapidamente. cometi três erros críticos no início: 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" "Fixar o bug de cálculo" The agent stopped, absorbed all the prompts, got confused, and created a Frankenstein version that did none of them well. 6 rollbacks, 3 horas perdidas, $ 23 em créditos Cost: Mistake #2: Underestimated UI complexity Me: "Add night mode" AI: Resultado: texto branco em fundo branco, botões invisíveis, desastre completo Proceeds to make 47 changes Patiently working through font/background mismatches took longer than expected. 3 days Mistake #3: Wasn't precise with instructions "Make it more intuitive" AI changed the entire navigation structure Bad prompt: What happened: "Change the 'Calculate' button color to blue (#0066CC) and increase font size to 16px" Exactly what I wanted Better prompt: What happened: A Magia do Encantamento 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." Esta instrução simples poderia ter me salvo . $50+ in wasted iterations Week 2: Reality Check (Days 8-14) Day 8-14: Travel and Trouble Viagem de verão (para o Japão), desacelerou-me, mas também me deu uma perspectiva sobre o que não estava funcionando. Things I learned while vibe coding from airport lounges: Hotel WiFi + Replit = frustração Erros de TypeScript são mais difíceis de depurar no celular The rollback button becomes your best friend Eu recomendo Replit como seu ponto de partida para codificação Vibe se você não sabe muito sobre codificação e implantação de aplicativos. Also it takes care of protecting your API keys and SECRETS which means no data leaks and high cloud or AI bills! Além disso, tem um agente de IA dedicado com o qual você pode conversar, entender o código, revisar o código e planejar seu trabalho ANTES de construir. Day 15: Existential Dread Recurring error to render the screen Still debugging Finally understand it's a TypeScript type issue Ainda quebrado Tuesday, 3:47 PM: Tuesday, 4:15 PM: Tuesday, 6:30 PM: Tuesday, 11:45 PM: Tomei a just to understand the code. whole day Deveria ter dito ao agente para usar Python (um idioma que eu entendo um pouco). O agente de IA estava codificando em TypeScript. Uma língua que eu realmente não conheço. Thank god for @Replit's rollback options. Day 16: The Credit Crisis Replit credits run out FAST. Lesson learned: Meu padrão de gastos: Semana 1: US $ 34 em créditos Week 2: $93 in credits (yikes!) Eu estava iterando rapidamente, fazendo mudanças, rolando de volta, tentando novamente. Orçamento $40 / semana máximo. Se eu atingir o limite, pare e reflita sobre por que eu estou queimando através de créditos. New rule: A escolha do Stack I integrated: for system emails (free tier = win). Basically to send emails to users. @Brevo 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. Semana 3: Feedback do usuário muda tudo (Dias 15-21) Day 17: Time for Feedback Depois de limpar os erros durante a viagem, comecei a caçar testadores. Posted in 3 founder Slack channels: "Building a financial planning tool that doesn't suck. Need critical feedback. DM if interested." Resposta em: crickets Day 18: The Humbling Finally got and to try the MVP. 1 friend 2 founders The feedback was... brutal: Issue #1: Financial calculations were off by 20% A founder's CAC calculation showed when it should have been . $47 $58.75 Esse erro de 20% poderia ter-lhes custado sua rodada da Série A. 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 Qualquer modelo com mais de 50 linhas de dados causou uma sobrecarga de memória. Issue #3: "Too many clicks to get to runway calculation" A coisa que os fundadores mais queriam (runway) foi enterrado 3 telas profundas. Isso foi definitivamente mais difícil do que os influenciadores de IA fazem parecer! Dia 20: Seis Horas do Inferno Os cálculos LTV/CAC foram consistentemente errados. The bug: 6 horas de depuração direta Time spent: @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 Be surgically precise with financial formulas. The fix: Bad prompt: Calculate LTV 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 Critical Lesson Learned 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 Um fundador cortou toda a complexidade: "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. Semana 4: O Pivô (Dias 22-30) Day 22: Language Regrets Starting with TypeScript instead of Python. Regret of the month: Quando as fórmulas financeiras se tornam complexas, passei mais tempo debugando a sintaxe do que construindo recursos. 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' Pick programming languages you actually understand for serious projects! Note to future self: Dia 23: O Desastre “Intuitivo” Replit credits burned through again. $11 in one afternoon. I built a "scenario comparison" feature that took Porque eu continuava dizendo “faça mais intuitivo” sem ser específico. 47 iterations "Make it more intuitive" Iteration 1: Mude todo o layout “Não, não é assim, mais intuitivo” Iteration 2: AI changes the color scheme "JUST MAKE IT INTUITIVE" Iteration 3: AI adds tooltips everywhere ...45 iterations later... 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 Publicado em Pergunta aos testadores: 5 founder Slack groups Results: 23 "looks interesting!" 😊 2 actual signups 😐 0 completed onboarding 😭 Conversion funnel: Interessados: 23 Signup: 2 (8.7%) Conclusão de Onboarding: 0 (0%) Making stuff people want ≠ Making stuff people actually use. Day 25: The API Awakening Founders kept asking: "Can it sync with QuickBooks?" "Sure, how hard can API integration be?" Me: [Researches QuickBooks API por 3 horas] What's required: Configuração do OAuth 2.0 Flow Webhook validation Mapeamento de dados entre o QuickBooks e o meu esquema Erro de gestão de limites de taxa Token refresh logic Accounting rules validation This isn't happening in vibe coding. Not anytime soon. Realization: Day 26: Precision in Prompts @MistralAI is great, but I learned you need for financial calculations. VERY specific prompts Bad prompt: Calculate runway Makes assumptions, might use wrong numbers What AI does: 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. Gets it right every time What AI does: Precisão em finanças.Não há espaço para ambiguidade. Day 27: Rollback Appreciation Day Usado o recurso de rollback do @Replit in one day. 12 times I tried to add "smart defaults" for SaaS metrics (based on industry benchmarks). What happened: Instead, I broke: O mecanismo de cálculo The export functionality The scenario comparison Autenticação do usuário (de alguma forma?) Desconhecido, desistiu depois de uma hora 30 seconds Time to fix manually: Time to rollback: Às vezes, o melhor código é o código que você não escreve. Day 28: The Hard Truth Depois de 4 semanas, eu admiti o que eu estava evitando: 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) Sometimes less is more. Day 29: The Best Feedback O comentário de um dos fundadores mudou toda a minha abordagem: "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 Números irrealistas Suggests improvements Answers "what if" questions Sometimes users tell you exactly what to build if you listen carefully enough. Dia 30: Um fundador que pagaria Publicou a versão escalada.Obteve feedback brutal, mas útil. Um dos fundadores disse: "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. The 30-Day Scorecard (Being Brutally Honest) Month 1 Statistics Development: 30 Days coding: $127 Replit credits spent: ~3,500 (mostly by AI) Lines of code written: 73 Rollbacks executed: Línguas aprendidas de maneira difícil: 1 (TypeScript) User Metrics: 23 Interested parties: 12 Actual signups: Onboarding concluído: 3 3 Completed models: 1 Would pay: Receita: 0 dólares Key Wins: 🎯 Found product-market fit signal (1 founder willing to pay) 🎯 Validated core problem (founders hate Excel) 🎯 Discovered simpler solution (advisor > tool) Key Losses: ❌ 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 ✅ Went from idea to testable MVP in 2 weeks Rapid prototyping: $127 total vs. $20K+ for developers Low initial investment: Try, fail, rollback, try again in minutes Quick iterations: Assistência de IA: ótimo para caldeiras e padrões padrão No interviews, no management, no equity No hiring headaches: The Challenges ⚠️ Gerenciamento de crédito: pode ficar caro rapidamente com muitas iterações AI struggles with precision in financial formulas Complex calculations: Limitações de integração: APIs empresariais precisam de desenvolvimento adequado Restrições linguísticas: fique com o que sabe ou pague o imposto de aprendizagem Precisão requerida: instruções vagas = tempo perdido e créditos Understanding AI-generated code is hard Debugging difficulty: Key Principles I Discovered 1. Be Surgically Precise with Instructions "Make it better" "Alterar a cor do botão para #0066CC, aumentar o tamanho da fonte para 16px, adicionar 8px padding" Don't say: Do say: 2 – Uma mudança de vez em quando Never give the AI multiple tasks in parallel. Wait for completion, review, then proceed. Bad workflow: "Add dark mode" "Fix the bug" "Improve performance" Good workflow: "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 Ele está lá por uma razão. eu rolou de volta 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. Saiba quando fazer 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 ✅ Still the fastest way to test ideas Vibe coding for rapid prototyping: Critical feedback > polite feedback Brutal honesty in user testing: O pivot para "conselheiro não ferramenta": Esta é a visão vencedora 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 What I'd Skip Entirely ⛔ - Nobody asked for it, took 3 days Night mode - Founders want function over form Perfect UI Promessas de integração - Valide primeiro o fluxo manual - 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. Não cinco nem dez. Fifty. Pergunte a eles: Show me your current financial model O que leva mais tempo para atualizar? What question do investors always ask? Quanto você pagaria por uma solução? This would have saved me 2 weeks and $$ in wasted effort. O que é o próximo? A abordagem inteligente: MVP progressivo I'm not building everything at once anymore. Here's the realistic path: Fase 1: Validar com codificação Vibe (Atual - Semanas 5-8) Build: ✅ Manual financial model builder ✅ AI advisor for validating assumptions ✅ Basic scenario planning (3 scenarios) ✅ Export to Excel/PDF Linguagem natural Q&A Get to 10 paying customers at $50/month Goal: What I'm trying to prove: Core value proposition works Users prefer this vs. spreadsheets AI advisor adds real value O motor econômico básico é suficiente Success criteria: 10 paid subscribers 40 Pelo menos 5 seriam "muito decepcionados" se o produto desaparecesse Fase 2: Se funcionar, vá Pro (Semanas 9-24) After 50-100 paying founders, consider: Recrutamento de desenvolvedores fintech experientes Integração em tempo real Adding enterprise security (SOC 2) Scaling infrastructure $50K-100K (bootstrap or small angel round) Budget: Quando se formar para além da codificação Vibe Vibe coding is great for: ✅ Rapid prototyping ✅ Basic CRUD operations ✅ Integração de IA (chamadas OpenAI/Mistral API) ✅ Export functionality ✅ User feedback and fast iteration ✅ Landing pages and marketing sites Where you'll hit walls: ❌ Complex financial formulas (cohort retention curves, NPV calculations) ❌ Enterprise API integrations (OAuth flows, webhook handling) Trabalhos de fundo para sincronização de dados ❌ Multi-tenant security architecture Otimização de desempenho (pesquisas sub-300ms) Características da colaboração em tempo real When you have 10+ paying customers asking for features that vibe coding can't deliver. The graduation threshold: If You're Building with Vibe Coding: A Checklist Save yourself time and money. Use this: Before You Start [ ] Choose a language you actually understand [ ] Set a credit budget ($X per week max) [ ] Define "done" for your MVP (write it down) [ ] Find 3 users who will test, not just say "sounds interesting" [ ] Entrevistar 10+ usuários potenciais primeiro [ ] Escreva o problema #1 que você está resolvendo Enquanto a construção [ ] One prompt at a time, wait for completion [ ] Define vague words ("intuitive", "clean", "simple") [ ] Validate ALL calculations manually [ ] Use rollback guilt-free [ ] Track crédito gastar diariamente [ ] 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 Want to Help? I'm looking for 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 Requirements: ✅ Pre-seed to Series A stage ✅ Currently use Excel/Sheets for financial planning Estar disposto a ser brutalmente honesto (apenas feedback crítico) ✅ Can commit to testing for 1 week What You Get: 🎁 Free lifetime access (worth $600/year) 🎁 Pedidos de características de prioridade 🎁 Direct access to me via WhatsApp 🎁 Seu logotipo na página "Construído com os fundadores" 7/10 (3 already filled) as of Nov 1, 2025 Spots available: DM me on Twitter . Want to test out what I built? Here is the link» How to apply: @RenjitPhilip https://runwayai.futureu.co @RenjitPhilip https://runwayai.futureu.co Prova Social (Sim, é cedo, mas é 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 "You answered my investor question in 30 seconds. It would have taken me 3 hours in Excel." — Sarah K., Marketplace Founder, Seed The Mission Kill the 47-tab Excel financial model. Every founder deserves: ✅ Real-time financial dashboards ✅ AI that explains the numbers Planejamento de cenários em segundos ✅ Investor-ready exports instantly O dia 31 começa amanhã. Follow along: #vibecoding #BuildInPublic @RenjitPhilip @RenjitPhilip - 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» P.S. https://runwayai.futureu.co https://runwayai.futureu.co