@masitecno

Fernando Castellanos

@masitecnoJoined June 2026

Practical notes from a backend developer debugging real-world systems.

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Fernando Castellanos's blogs

Backend Debugging Notesbackend-debugging.hashnode.dev3 posts

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FCFernando Castellanosbackend-debugging.hashnode.dev14h ago · 17 min read

From Smoke Tests to Production Truth: Lessons from Load Testing Five APIs with Locust

What five production APIs taught me when a green smoke test stopped being enough The short version. An API that returns HTTP 200 in a smoke test has told you almost nothing about whether it survives

FCFernando Castellanosbackend-debugging.hashnode.devJun 30 · 8 min read

The Bug Wasn't in Our Code

BACKEND ENGINEERING · DEBUGGING QA filed the regression at 4:50 on a Friday. The endpoint had worked the day before. The deployment that morning had gone green. Git showed nothing that touched the fai

FCFernando Castellanosbackend-debugging.hashnode.devJun 25 · 10 min read

How I Use AI Assistants for Debugging Without Trusting Them Blindly

Key takeaways Treat AI output as a hypothesis to verify, never as evidence or a final answer. Ask the AI to map categories of causes — code, data, config, database, infrastructure — instead of "the c

Fernando Castellanos

About

Available for

Fernando Castellanos's blogs

Recently published

From Smoke Tests to Production Truth: Lessons from Load Testing Five APIs with Locust

The Bug Wasn't in Our Code

How I Use AI Assistants for Debugging Without Trusting Them Blindly

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Fernando Castellanos

About

Available for

Fernando Castellanos's blogs

Recently published

From Smoke Tests to Production Truth: Lessons from Load Testing Five APIs with Locust

The Bug Wasn't in Our Code

How I Use AI Assistants for Debugging Without Trusting Them Blindly