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Thoughts & Writing.

On building AI products, navigating fintech from the inside, and what happens when a business executive starts shipping code.

15 articles published

Blueprint cross-section of a building under an X-ray scan, with hidden dependencies highlighted in lime

Featured

Jul 29, 2026AI Integration6 min read

IBM calls it a building inspector. We ran the inspection.

IBM says AI coding agents work like building inspectors. We ran the five-step loop on a production SaaS — what held up, what broke, and the steps we'd add.

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Aug 12, 2025web development5 min

Server Actions and Mutations in Next.js 15

How Server Actions work in Next.js 15: defining them, why each one is a public endpoint, pending states with useTransition, and a data access layer.

Piotr

Apr 10, 2025web development10 min

Build the API with Next.js only

When and how to build an API with Next.js alone: Route Handlers, dynamic routes, proxying an existing backend, webhooks, custom auth and shared wrappers.

Piotr

Oct 20, 2024web development10 min

Some of the little tips & best practices for React/Next.js developers

Ten practical habits for React and Next.js: no hardcoded values, a clear folder structure, simple components, and filters and pagination kept in the URL.

Piotr

Sep 15, 2024web development15 min

Next.js 14 some of my key observations after one year of the extensive use.

Next.js 14 App Router lessons from a year of heavy use: 'use client' placed too high, server and client component myths, and leaking server data.

Piotr

Jun 13, 2024AI Integration8 min

Implementing an AI-powered Shopping Assistant

Building an AI shopping assistant for a MedusaJS store with the Vercel AI SDK: Core, UI and RSC, plus the actions file and the page code.

Piotr

Apr 1, 20248 min

Clerk, Next.js 14 and Drizzle ORM boilerplate

A Next.js 14 starter with Clerk authentication and Drizzle ORM on Neon Postgres, step by step: provider, middleware, components and database setup.

Piotr

Feb 3, 2024web development15 min

NextAuth Credentials — easy signup & login with email & password (Next.js 14 App router and Zod resolver)

Email and password sign-up and login in Next.js 14 with NextAuth Credentials, Zod validation and Postgres, including restricted pages.

Piotr

Jan 8, 2024AI Integration3 min

Assistants API (OpenAI): Real-world simple example - money transfer online FAQ

A hands-on test of the OpenAI Assistants API: a money-transfer FAQ assistant built step by step, from file retrieval to threads, runs and responses.

Piotr

Dec 1, 2023web development8 min

Next.js 14 payment gateway integration with P24 (Przelewy24)

Adding Przelewy24 (P24), the Polish payment gateway, to a Next.js 14 shop: a cart modal that starts the payment and the API endpoint behind it.

Piotr

Nov 22, 2023web development10 min

Easy Stripe checkout with use-shopping-cart and Next.js 14

Stripe Checkout in a Next.js 14 shop with use-shopping-cart: the cart provider, cart modal, add-to-cart button, and products and prices in Stripe.

Piotr

Jul 16, 2023analytics3 min

GPT-4 Model help in Geo Mapping at the large scale.

Can GPT-4 help with geo-mapping at scale? A real business-risk task, checking which sales points fall inside an area of interest, prompt by prompt.

Piotr

Jul 6, 2023analytics3 min

Get full address from geo coordinates using Python for free

Turning geo coordinates into full addresses for 4,000+ records with Python, pandas and the free Nominatim geocoder.

Piotr

Apr 5, 2023analytics3 min

Python with Pgeocode and Pandas. Postal codes to geo coordinates

Converting postal codes to latitude and longitude offline with Python, pgeocode and pandas, with distance queries and data for 83 countries.

Piotr

Feb 4, 2022analytics3 min

Pydeck, Python data visualization. Column Layer on Carto maps

Visualising large geo datasets in Python with pydeck (deck.gl) and pandas: a 3D column layer on Carto basemaps.

Piotr

vacalocalabs.com

Let's build something.

I co-founded Vacaloca Labs, a boutique studio building web, data and AI products. Working with my co-founder across strategy and design, I lead software architecture and hands-on technical delivery, from product definition through implementation and deployment.

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