Cheatsheets.
Dense, scannable one-pagers for the things you look up constantly — complexity, decoding params, status codes, latency numbers, the agent loop. Print them, bookmark them, share them.
Big-O Complexity
Time and space complexity of the data structures and algorithms you use every day.
Algorithms · open →LLM Sampling & Decoding
Every knob that shapes how a language model picks its next token — and sensible presets.
AI & LLMs · open →HTTP Status Codes
The response codes worth memorizing, grouped by class, with when to use each.
Web · open →System Design Napkin Math
The latency numbers, constants, and powers of ten for back-of-the-envelope estimates.
Systems & Backend · open →The Agent Loop Cheatsheet
The runtime of an AI agent on one page — the loop, context, failure modes, and defenses.
AI & LLMs · open →Loop Engineering
Running agents without being the keyboard — loop types, guards, building blocks, and failure modes on one page.
AI & LLMs · open →Sorting Algorithms
Every common sort at a glance — time, space, stability, and which one to reach for.
Algorithms · open →Graph Algorithms
Traversal, shortest paths, and spanning trees — with the one to reach for in each case.
Algorithms · open →Dynamic Programming Patterns
The DP recipe, the classic templates, and how to recognize a DP problem in the wild.
Algorithms · open →Transformer Math
The napkin formulas behind every scaling, memory and cost conversation — params, FLOPs, KV cache, VRAM.
AI & LLMs · open →GPU Numbers Every AI Engineer Should Know
VRAM, bandwidth, TFLOPs and rental prices for the cards that matter — plus the rules of thumb they imply.
AI & LLMs · open →Prompt Patterns
The dozen prompting techniques that actually move quality, with the one-line version of when to use each.
AI & LLMs · open →Evals & Metrics
Every metric you need to evaluate LLMs, RAG and agents — what it measures and when it lies.
AI & LLMs · open →MCP Quick Reference
The Model Context Protocol on one page — primitives, transports, message flow, security rules.
AI & LLMs · open →Git Survival Guide
The commands you actually reach for — daily flow, undo anything, branches, and the ones you google every time.
Systems & Backend · open →SQL Quick Reference
Joins, aggregation, window functions and the query-shape patterns interviews and dashboards both live on.
Systems & Backend · open →Regex Without Tears
The 20% of regular expressions that solves 95% of problems — tokens, anchors, groups, lookarounds, flags.
Web · open →Bash & The Terminal
Pipes, process control, the text-tool trinity and the shell one-liners that replace small programs.
Systems & Backend · open →Pandas & NumPy
The data-wrangling operations every ML notebook runs on — selection, groupby, joins, reshaping, vectorization.
AI & LLMs · open →kubectl Quick Reference
The Kubernetes commands you reach for during deploys, debugging and 2am incidents — organized by situation.
Systems & Backend · open →Docker Survival Guide
The container commands you reach for daily — build, run, debug, clean up — plus the Dockerfile lines that actually matter.
Systems & Backend · open →Linux Debugging Toolkit
When a process is slow, stuck, or leaking — the commands that tell you what it is actually doing: strace, lsof, perf, and friends.
Systems & Backend · open →Network CLI Toolkit
Diagnose DNS, connections, and packets from the terminal — dig, ss, tcpdump, ip, and nc, with the flags that get answers fast.
Systems & Backend · open →Vim Survival Guide
Enough Vim to edit confidently on any server — modes, motions, and the operator+motion grammar that makes it click.
Systems & Backend · open →tmux Quick Reference
Keep sessions alive across disconnects and split your terminal like a pro. Everything is prefix (Ctrl-b) then a key.
Systems & Backend · open →curl Quick Reference
Talk to any HTTP API from the terminal — headers, bodies, auth, downloads, and the flags that make debugging painless.
Systems & Backend · open →jq Quick Reference
Slice, filter, and reshape JSON on the command line. Pipe curl into jq and stop eye-parsing giant payloads.
Systems & Backend · open →psql Quick Reference
The PostgreSQL CLI’s backslash meta-commands — inspect schemas, time queries, and stay productive without a GUI.
Systems & Backend · open →redis-cli Quick Reference
The commands and data-structure verbs you use against Redis — strings, hashes, lists, sets, sorted sets, and TTLs.
Systems & Backend · open →Kafka CLI Quick Reference
Create topics, produce and consume messages, and inspect consumer-group lag from the command line.
Systems & Backend · open →Python Standard Library
The batteries-included modules that mean you rarely need a dependency — collections, itertools, functools, pathlib, and more.
Systems & Backend · open →TypeScript Types Quick Reference
The type-system features you actually use — unions, generics, utility types, narrowing, and the syntax that trips people up.
Web · open →React Hooks Quick Reference
Every core hook, what it is for, and the rules and gotchas that cause most React bugs.
Web · open →CSS Flexbox & Grid
Stop guessing at layout. The properties that actually center, distribute, and arrange things — flexbox for one dimension, grid for two.
Web · open →Data Structure Complexity
The full time/space table for every structure you reach for — average and worst case, at a glance. The interview reference.
Algorithms · open →HTTP Headers Quick Reference
The request and response headers that control caching, content, auth, CORS, and security — what each one does and sane values.
Web · open →SQL Window Functions
The analytics superpower most people skip: compute running totals, rankings, and row-to-row comparisons without collapsing your rows.
Systems & Backend · open →Git Advanced (Rebase, Bisect, Worktree)
Beyond add/commit/push — rewrite history cleanly, hunt a bug with binary search, and juggle branches without stashing.
Systems & Backend · open →Keyboard Shortcuts (Editor & Terminal)
The muscle-memory keys that make you faster in VS Code, the shell, and the browser devtools — the ones worth memorizing.
Web · open →Claude Code (Agentic CLI)
The moves that make Claude Code fast — slash commands, file references, plan mode, memory, subagents, MCP, and headless runs.
AI & LLMs · open →API Security Checklist
The controls that keep an API from becoming a breach — auth, authorization, input handling, transport, and the OWASP API Top-10 traps.
Systems & Backend · open →The Forward Deployed Engineer Playbook
The whole role on one sheet — discover the problem, prototype fast, integrate, deploy in the customer’s world, demo, harden, hand off.
Systems & Backend · open →Customer Discovery Questions
The questions that surface the real problem, the constraints, and the definition of success — before you write a line of code.
Systems & Backend · open →The Demo Checklist
A demo is a performance, not a code review. Prep it, run it, and recover from live failure — then follow up while it’s hot.
Systems & Backend · open →Integration Debugging Playbook
When the API call, webhook, or auth handshake fails at the customer’s edge — the systematic checklist that finds it fast.
Systems & Backend · open →Deployment Targets (Cloud → Air-Gapped)
Where will it actually run? The tradeoffs across SaaS, the customer’s cloud/VPC, on-prem, and air-gapped — and what each costs you.
Systems & Backend · open →Security & Compliance Quick-Ref (FDE)
Enough to earn a security team’s "yes": what SOC 2 / HIPAA / GDPR actually ask, how to handle data and secrets, and what reviews check.
Systems & Backend · open →POC → Production Checklist
The gate a demo must clear to become a system people depend on: reliability, observability, security, and a real handoff.
Systems & Backend · open →The FDE Interview Question Bank
Fifty-plus reported Forward Deployed Engineer interview questions across all nine round archetypes — each with the model answer shape and a link to practise it.
Systems & Backend · open →Built for the lookup, not the lesson.
When you already know it
A cheatsheet is for the thing you understand but can't recall on the spot — the exact flag, the complexity of that operation, the status code, the p99 you should expect. Reach for it mid-task, grab the one line, get back to work.
When you're still learning it
If a row raises more questions than it answers, that's the signal to go deeper — most sheets link out to the handbook, lab, or system design that explains the idea in full. Skim the sheet first, then follow the thread.
Organized by domain
Sheets are grouped by category so the one you need sits next to its neighbours — AI and LLMs, systems and backend, algorithms, and the everyday developer tools. Print one, bookmark it, or keep the tab open next to your editor.