Developer References
Interactive references for the lookups you do often enough to need, but not often enough to memorize: what an HTTP status code means and how it differs from its neighbors, what chmod 755 actually grants, which Unicode code point a character is, or what a prompt will cost across different LLMs.
4 reference tools
HTTP Status Codes
Searchable reference for all HTTP status codes
Chmod Calculator
Calculate Unix file permissions with visual checkboxes
AI Token Counter & Cost Estimator
Estimate how many tokens your prompt costs, and what it'd run across Claude, GPT, and Gemini
Unicode Explorer
Search and inspect Unicode characters by name, code point, or symbol
Guides
🧾 How to Estimate Your LLM API Costs Before You Get the Bill
A practical walkthrough of how LLM API pricing actually works — tokens, input vs output cost, why a long system prompt costs more than you think — so you can estimate spend before you ship, not after.
🌐 nginx 502, 504, and 403 Errors Explained (and How to Actually Fix Them)
502 means nginx never got a valid response. 504 means it got one too slowly. 403 means nginx itself is blocking you before your app ever sees the request. Here's how to tell them apart and fix the real cause of each.
💾 Linux 'No Space Left on Device' and 'Permission Denied': The Errors That Lie to You
df -h says you have gigabytes free but writes still fail. chmod 777 doesn't fix a permission error that isn't actually about Unix permissions. Here's what's really going on and the exact commands to find it.
🐳 standard_init_linux.go:211: exec user process caused: no such file or directory — Docker Fix
The most common cause of this Docker error is Windows CRLF line endings in shell scripts. Learn how to detect, fix, and prevent it with .gitattributes and Dockerfile workarounds.
🔐 chmod: invalid octal value — Permission Fix Guide
Invalid octal value errors in chmod happen when you use 8 or 9 in an octal number, or miscount the digits. Learn the full octal permission system and how to fix each case.
🚫 HTTP 401 vs 403: Unauthorized vs Forbidden Explained
HTTP 401 Unauthorized and 403 Forbidden are both auth-related errors but mean different things. Learn the exact difference and how to fix each one.