Buglyst Blog
Learn to debug under pressure.
Playbooks for fast pattern recognition, guides for the full investigation, and articles for the engineering judgment around the edges.
17 playbooks · 509 guides · 95 articles · 12 linked practice labs ·skip to practice
Fast pattern recognition for the production failures engineers see most often.
17 playbooks
Debugging Env Var Issues
A concise checklist for incidents where local works but CI, staging, or production changes behavior.
Debugging Cache Stampedes
How to recognize and contain request spikes when cached data expires.
Debugging CORS Origin Bugs
A practical way to inspect origin parsing, credentials, and header behavior.
Debugging Retry Bugs
Retry issues often hide the first failure and create duplicate work.
Debugging Timezone Bugs
Time bugs usually live at day boundaries, DST changes, and unit conversions.
Debugging Pagination Bugs
Pagination bugs hide in boundary math, cursor reuse, and new records arriving between pages.
Structured investigations for the failure modes engineers meet in real systems.
FastAPI Dependency Injection Fails: Missing `async def` and Scope Mismatches
A practical guide to debugging FastAPI dependency injection errors caused by missing async def, incorrect scope, or parameter mismatches.
Django Celery Task Not Executing: A Field Guide to Silent Failures
Diagnose why your Celery task won't run in Django — from broker misconfigurations to worker crashes. Commands, logs, and fixes included.
Debugging FastAPI 422 Validation Errors: Pydantic Model Mismatches
A systematic approach to diagnosing and fixing HTTP 422 validation errors in FastAPI, focusing on Pydantic model mismatches and request parsing issues.
FastAPI Background Task Not Running: Debugging Silent Failures
A practical debugging guide for when FastAPI background tasks silently fail to execute, covering lifespan events, async context, and server configuration.
Debugging FastAPI CORS Errors from Frontend Requests
A practical guide to diagnosing and fixing CORS errors when a frontend makes requests to a FastAPI backend.
Python Multiprocessing PicklingError: How to Debug
A practical guide to diagnosing and fixing PicklingError when using Python's multiprocessing module. Covers pickling scope issues, lambda closures, and dynamic classes.
Long-form thinking on debugging habits, observability, and the systems around the bug.
Tracking Down a 200 MB Leak with Python Memory Profilers
A production API was silently leaking 200 MB of RAM every hour. Here's how memory profilers found the culprit—a forgotten NumPy array reference—and how you can apply the same techniques.
Reading CPU Flame Graphs: What the Hot Colors Actually Tell You
Flame graphs are everywhere, but most engineers read them wrong. Here's how to identify real bottlenecks, avoid common misinterpretations, and turn profile data into actionable fixes.
When Logs Lie: The Gaps Between What You Log and What Actually Happened
Logs are the first thing we reach for during an incident. But they can be misleading, incomplete, or outright wrong. Here's when to trust them and when not to.
Adding Observability to a 500K-Line Monolith Without a Rewrite
Adding structured logging, distributed tracing, and metrics to a legacy monolith without a full rewrite. Real code examples and a war story from a 500K-line codebase.
Distributed Tracing: Following a Single Request Across Microservices
Distributed tracing lets you follow a request as it hops across services. I'll show you how trace context propagates, why sampling matters, and how tracing helped us debug a 5-second latency spike in production.
Structured Logging in JSON: Fields, Schemas, and Pitfalls from Production
A practical guide to designing JSON log schemas that are queryable, consistent, and actually useful in production — with field recommendations and a war story.