Nicolás Duque https://nicolasduque.com Notes on shipping React/Node.js products and putting LLMs and AI agents into production. Written by Nicolás Duque, senior full-stack engineer and former tech lead. en LLMs in production: the hard part is the contract around the model https://nicolasduque.com/blog/llms-in-production-the-contract-around-the-model/ https://nicolasduque.com/blog/llms-in-production-the-contract-around-the-model/ Wed, 16 Sep 2026 12:00:00 GMT What I learned putting OpenAI, Anthropic and Gemini behind an accounting product: schemas, deterministic checks, confidence thresholds and a human review queue. Designing an MCP server an LLM can use safely https://nicolasduque.com/blog/designing-an-mcp-server-an-llm-can-use-safely/ https://nicolasduque.com/blog/designing-an-mcp-server-an-llm-can-use-safely/ Wed, 19 Aug 2026 12:00:00 GMT Lessons from exposing market data, account data and a trade journal to Claude through MCP: grouping tools, failing clearly, and never letting the model place an order. Reading bank notification emails to track spending in Colombia https://nicolasduque.com/blog/reading-bank-emails/ https://nicolasduque.com/blog/reading-bank-emails/ Wed, 05 Aug 2026 12:00:00 GMT Colombian banks don't offer open APIs to regular developers, so Nora reads the transaction alerts they already send by email. Here's how the pipeline works. Rules first, LLM second: categorizing Colombian bank transactions https://nicolasduque.com/blog/rules-first-llm-second/ https://nicolasduque.com/blog/rules-first-llm-second/ Wed, 15 Jul 2026 12:00:00 GMT In Nora, my personal-finance app, the LLM is the last resort, not the first step. Here's the pipeline and why every AI answer becomes a rule. Dashboards from JSON schemas: replacing spreadsheet reports https://nicolasduque.com/blog/json-schema-dashboards/ https://nicolasduque.com/blog/json-schema-dashboards/ Wed, 10 Jun 2026 12:00:00 GMT At LeoVegas I built a Node.js service and a schema-driven dashboard framework with pluggable database connectors, so product managers could stop building reports by hand. Rules as data: onboarding customers without shipping code https://nicolasduque.com/blog/rules-as-data/ https://nicolasduque.com/blog/rules-as-data/ Wed, 27 May 2026 12:00:00 GMT At KitchenSync every restaurant had its own accounting rules. Moving those rules out of code and into configuration changed how we onboarded customers. What I learned leading a team of four engineers https://nicolasduque.com/blog/leading-a-team-of-four/ https://nicolasduque.com/blog/leading-a-team-of-four/ Wed, 13 May 2026 12:00:00 GMT Small pull requests, mandatory review, CI, quality audits and settling technical debates with data: the habits that kept quality up at KitchenSync. Three ways LLMs fail in production, and what to do about each https://nicolasduque.com/blog/three-ways-llms-fail/ https://nicolasduque.com/blog/three-ways-llms-fail/ Wed, 22 Apr 2026 12:00:00 GMT API errors, broken output and answers that look right but aren't. Each one needs a different defense. A dev team of agents, each in its own git worktree https://nicolasduque.com/blog/a-dev-team-of-agents-in-git-worktrees/ https://nicolasduque.com/blog/a-dev-team-of-agents-in-git-worktrees/ Wed, 08 Apr 2026 12:00:00 GMT How I turned Claude Code into a small team: a project manager, backend, frontend, database and QA agents working in parallel without stepping on each other. Five levers for LLM cost that matter more than a clever prompt https://nicolasduque.com/blog/five-levers-for-llm-cost/ https://nicolasduque.com/blog/five-levers-for-llm-cost/ Wed, 25 Mar 2026 12:00:00 GMT Model per task, fewer tokens, caching, batching and measuring every request: the cost controls I rely on when LLMs run inside a real product. One shared TypeScript library for every service, without a god library https://nicolasduque.com/blog/a-shared-typescript-library/ https://nicolasduque.com/blog/a-shared-typescript-library/ Wed, 11 Mar 2026 12:00:00 GMT At KitchenSync I designed a shared TypeScript library with more than 16 modules used across the whole platform. Here's how to keep something like that useful instead of dangerous. Shipping software under IEC 62304 https://nicolasduque.com/blog/shipping-under-iec-62304/ https://nicolasduque.com/blog/shipping-under-iec-62304/ Wed, 25 Feb 2026 12:00:00 GMT What building a triage module for a digital healthcare platform taught me about traceability, risk and documented change, and why those habits are worth keeping outside healthcare. Turning a mobile app into a white-label SaaS https://nicolasduque.com/blog/white-label-mobile-saas/ https://nicolasduque.com/blog/white-label-mobile-saas/ Wed, 11 Feb 2026 12:00:00 GMT How we refactored Doktor24's mobile app so partners could get their own branded version from configuration, with a CI/CD pipeline that builds each brand. Backend for frontend: one API per kind of client https://nicolasduque.com/blog/backend-for-frontend/ https://nicolasduque.com/blog/backend-for-frontend/ Wed, 28 Jan 2026 12:00:00 GMT At Doktor24, patients, practitioners and configurators needed very different things from the same platform. Node.js BFF services gave each client an API shaped for it. Micro-frontends with Module Federation: what we gained and what it cost https://nicolasduque.com/blog/micro-frontends-with-module-federation/ https://nicolasduque.com/blog/micro-frontends-with-module-federation/ Wed, 14 Jan 2026 12:00:00 GMT At Doktor24 we split a healthcare web platform into micro-frontends so teams could ship on their own schedule. Here's the reasoning, the trade-offs, and when I wouldn't do it.