Shopify

The Shopify Cart Bug That Only Happens on Slow Connections

Items vanish from the cart, quantities are wrong, and it never reproduces on your machine. Throttle your network and it appears every time.

Bug Hunt

The Bug That Only Happened on Tuesdays

A weekly export failed every Tuesday and worked every other day. Three wrong hypotheses later, the cause was a date format string nobody had looked at in four years.

Performance

How to Read a Flame Graph in Sixty Seconds

Width is time, stacking is call depth, and left to right means nothing. Once those three facts land, flame graphs become the fastest way to find a bottleneck.

Opinion

Choose Boring Technology, Except Where It Matters

The advice is right and incomplete. The interesting question is where to spend your limited budget for novelty.

Node.js

ERR_REQUIRE_ESM: The Complete Guide to Why Your Import Broke

The error that shows up when a dependency goes ESM only. What it means, the five ways to fix it, and how to pick the right one.

Debugging

Recovering Work After a Bad git reset --hard

Your commits are almost certainly still there. Here is how reflog works, what it cannot save, and the recovery path for each case.

Kubernetes

CrashLoopBackOff: A Complete Diagnostic Flowchart

CrashLoopBackOff is not an error, it is a symptom with about nine distinct causes. Here is how to identify which one you have in under three minutes.

Networking

redirect_uri_mismatch and the Rest of OAuth Debugging

OAuth errors are unhelpful by design, because detailed errors would help attackers too. Here is how to work out what is actually wrong.

AI

Testing an LLM Feature When the Output Is Different Every Time

You cannot assert equality on a model response. You can assert a lot of other things, and most teams assert none of them.

Debugging

How Breakpoints Actually Work: INT3, ptrace, and the Debugger Contract

Setting a breakpoint rewrites your program's machine code while it runs. Here is the mechanism, from the 0xCC byte up to why conditional breakpoints are slow.

React

Hydration Failed Because the Initial UI Does Not Match: Every Cause, Ranked

A complete diagnostic guide to React hydration mismatches: the eight real causes ranked by how often they actually happen, with the fix for each.

PostgreSQL

The Database Migration That Locked the Table for Nine Minutes

Adding a column should be instant. Sometimes it is not, and the difference is worth knowing before you run it in production.