Topics

Topics are the durable knowledge base. Each topic lives at topics/<category>/<slug>/index.md and can have subtopics underneath it.

AI

• AI, category overview
• Prompt Engineering, crafting LLM inputs to reliably elicit a target output
  • Context Window Management
  • Prompt Injection Defense
  • Structured Outputs
  • Templates
• Natural Language Processing, classical NLP, spaCy pipelines, NLTK corpus analysis, sparse classifiers, and where LLMs fit
  • NLTK
  • spaCy
• AI Harness Development, the scaffolding around an LLM that turns it into something useful
  • Context Engineering
  • Permission Models
  • Tool Design
• RAG (Retrieval-Augmented Generation), grounding LLM responses in external knowledge
  • Chunking
  • Embeddings
  • Hybrid Search
  • Reranking
• AI Skill Development, packaged, invocable capabilities loaded on demand
  • Writing a First Skill
  • Frontmatter and Discovery
  • Skill vs Tool vs Agent
  • Patterns from a Production Skill Library
• AI Coding Tool Blindspots, predictable failure modes of modern AI coding assistants
  • Benchmark Contamination
  • Prompt Injection
  • Slopsquatting
• DESIGN.md, Google Labs’ open-source format for giving agents a persistent design-system understanding
• Context Development Lifecycle, Patrick Debois’s generate-evaluate-distribute-observe framework for managing organizational context as a software artifact
• Model Distillation, training capable smaller models from larger ones
  • Theory and math, soft targets, temperature scaling, KL divergence loss, DistilBERT
  • LLM methods, SFT from outputs, explanation tuning, DPO, pretraining-time distillation
  • Distillation prompts, Alpaca, Orca, Orca 2, and Phi prompt examples
  • Case studies, Alpaca through DeepSeek-R1-Distill with costs and results
  • Implications, originality, first-mover advantage, IP, and capability hierarchy
• LLM reasoning benchmarks and metrics, 8-part series on what the numbers on the leaderboards actually mean
• AI text tells, the patterns that reveal LLM-generated text and the training dynamics that produce each one
• LLMs vs. agentic AI vs. AI agents, three distinct concepts: the base model, the loop-plus-tools architectural pattern, and specific implementations
• Deep Learn skill, a Claude Code skill implementing 15 learning science patterns for durable retention of any knowledge base
  • Knowledge and reasoning, MMLU, MMLU-Pro, GPQA Diamond, HLE, ARC-AGI
  • Math benchmarks, GSM8K, MATH, AIME, FrontierMath
  • Coding benchmarks, HumanEval, LiveCodeBench, SWE-bench and variants
  • Agent benchmarks, Terminal-Bench, TAU-bench, OSWorld, WebArena, GAIA
  • Long-context benchmarks, NIAH, RULER, LongBench, U-NIAH
  • Multimodal benchmarks, MMMU, MathVista, ChartQA, DocVQA
  • Evaluation methodology and metrics, LMArena, LLM-as-judge, pass@k, contamination

Computer Science

• CS, category overview
• Data Structures, the top 10 interview data structures with Python code
  • Arrays
  • Strings
  • Hash Tables
  • Linked Lists
  • Stacks
  • Queues
  • Heaps
  • Binary Trees
  • Graphs
  • Tries
  • Radix Tree
• Coding Problems, 150 problems across 18 categories, each with brute-force, improved, and optimal Python approaches
  • Arrays & Hashing
  • Two Pointers
  • Sliding Window
  • Stack
  • Binary Search
  • Linked List
  • Trees
  • Tries
  • Heap / Priority Queue
  • Backtracking
  • Graphs
  • Advanced Graphs
  • 1-D Dynamic Programming
  • 2-D Dynamic Programming
  • Greedy
  • Intervals
  • Math & Geometry
  • Bit Manipulation
• Coding Concepts, approach tactics that explain why coding-problem solutions work
  • Array Scans
  • Two Pointers
  • Fast and Slow Pointers
  • Sliding Window
  • Prefix Sums
  • Difference Arrays
  • Hash Map Counting
  • Sorting as Preprocessing
  • Binary Search
  • Binary Search on Answer
  • Modified Binary Search
  • Intervals
  • Merge Intervals
  • Greedy Algorithms
  • Greedy Exchange Arguments
  • Dynamic Programming
  • Memoization
  • Tabulation
  • State Compression
  • Knapsack Patterns
  • Sequence DP
  • Grid DP
  • Backtracking
  • Subsets and Combinations
  • Permutations
  • Constraint Search
  • Tree Traversal
  • DFS
  • BFS
  • Graph Traversal
  • Topological Sort
  • Union Find
  • Shortest Paths
  • Dijkstra
  • Bellman-Ford
  • Flood Fill
  • Heap and Priority Queue
  • Top K
  • K-way Merge
  • Monotonic Stack
  • Monotonic Queue
  • Stack Parsing
  • Trie Prefix Search
  • Bit Manipulation
  • Bitmask State
  • Linked List Pointer Rewiring
  • Cycle Detection
  • Recursion
  • Divide and Conquer
  • Simulation
  • Math and Number Theory
• Haversine Distance, great-circle distance with Python/SQL/JavaScript, and when to upgrade to Vincenty or Karney
• Vehicle Routing Problem, CVRP, VRPTW, pickup-and-delivery, and what Google OR-Tools actually does
  • Capacitated VRP
  • Time Windows (VRPTW)
  • Pickup and Delivery
  • Solution Approaches
• Functional Core, Imperative Shell, Gary Bernhardt’s architecture pattern
• Flight Itinerary with Transfers, time-respecting paths in a temporal graph: DFS, BFS, Dijkstra, and the time-expanded graph framework
• Graph Theory, terminology, graph types, components, SCCs, DAGs, bipartite graphs, and weighted-graph problem modeling
• Sentinel Values, the “impossible” placeholder pattern across DP, shortest-path, search, and linked-list problems
• Technology Laws, named laws and principles every software engineer will encounter
  • Team dynamics, Conway’s Law and Brooks’s Law
  • Performance math, Amdahl’s Law and Little’s Law
  • UI quantitative laws, Fitts’s Law and Hick’s Law
  • API design, Hyrum’s Law, Postel’s Law, and POLA
  • Metrics and estimation, Goodhart’s Law, Pareto, Hofstadter, 90-90 Rule, Parkinson’s Law
  • Systems thinking, Gall’s Law, Leaky Abstractions, Chesterton’s Fence, Tesler’s Law
  • Code quality, Kernighan’s Law and the Law of Demeter
  • Network effects, Metcalfe’s Law and Reed’s Law
  • Hardware and software, Moore’s Law and Wirth’s Law
  • Security, Schneier’s Law
• Named Algorithms, the canon worth knowing by sight
  • Kadane’s algorithm, maximum contiguous subarray sum and its variants
  • Dijkstra’s algorithm, single-source shortest paths on non-negative weighted graphs
  • Breadth-First Search, shortest path in unweighted graphs, level-by-level traversal
  • Depth-First Search, cycle detection, topological sort, connected components
  • Floyd’s tortoise and hare, cycle detection and cycle-start location in $O(1)$ space
  • Bellman-Ford, shortest paths with negative edge weights
  • Kahn’s algorithm, topological sort via BFS with natural cycle detection
  • Tarjan’s algorithm, strongly connected components in one DFS pass
  • KMP, linear-time substring search via the failure function
  • Quickselect, kth smallest in expected $O(n)$ time
  • Merge sort, $O(n log n)$ guaranteed stable sort, inversion counting
• Design Patterns, the 23 Gang of Four patterns grouped by intent: creational, structural, and behavioral, with TypeScript, Python, and Go implementations
  • Builder, step-by-step object construction with a fluent interface
  • Facade, a simplified surface over a complex subsystem
  • Flyweight, shared intrinsic state to reduce memory use
  • Command, requests as first-class objects with undo and queuing
  • Observer, automatic notification of dependents on state change
  • Strategy, swappable algorithm families
  • Factory, centralized object creation with Factory Method and Abstract Factory
  • Decorator, behavior added by wrapping without subclassing
  • Singleton, one instance, global access
  • Adapter, incompatible interfaces made compatible
  • Proxy, controlled access through a surrogate
• Kademlia DHT, XOR metric, k-buckets, iterative lookup, and the four RPCs behind BitTorrent mainline DHT, IPFS, and Ethereum devp2p

Python

• Python, category overview
• The Ellipsis (...), the built-in singleton and its four roles: placeholder body, type hint argument, NumPy slice, and stub marker
• List Comprehensions, the four forms (list, dict, set, generator), when to use each, and where they become a liability
• Async in Python, coroutines, the event loop, tasks, and asyncio.gather, plus when async helps and when it doesn’t

Networking

• Networking, category overview
• Part 1: Introduction to Networking, network types, topologies, and devices
• Part 2: The OSI Model, seven layers, encapsulation, and troubleshooting
• Part 3: The TCP/IP Model, four-layer stack, TCP vs UDP, and common ports
• Part 4: Physical Layer and Cabling, copper, fiber, and wireless media
• Part 5: Data Link Layer and Ethernet, frames, MAC addresses, and ARP
• Part 6: Switching Fundamentals, MAC tables, switching methods, and VLANs intro
• Part 7: VLANs, virtual LANs, 802.1Q trunking, and VTP
• Part 8: Inter-VLAN Routing, router-on-a-stick, SVIs, and Layer 3 switching
• Part 9: Spanning Tree Protocol, STP, RSTP, PortFast, and BPDU Guard
• Part 10: IPv4 Addressing and Subnetting, binary, CIDR, VLSM, and subnetting math
• Part 11: IPv6 Addressing, address types, SLAAC, DHCPv6, and NDP
• Part 12: Routing Fundamentals, routing tables, AD, metrics, and longest-prefix match
• Part 13: Static Routing, static routes, default routes, and floating static routes
• Part 14: OSPF, link-state routing, areas, DR/BDR, and SPF algorithm
• Part 15: EIGRP, DUAL algorithm, feasible successors, and fast convergence
• Part 16: NAT and PAT, static NAT, dynamic NAT, PAT overload, and NAT64
• Part 17: DHCP and DNS, DORA process, relay agents, DNS hierarchy, and record types
• Part 18: Access Control Lists, standard vs extended ACLs, wildcard masks, and placement rules
• Part 19: Network Security Fundamentals, port security, DHCP snooping, 802.1X, and VPNs
• Part 20: WAN Technologies and Network Automation, MPLS, SD-WAN, NETCONF, Python, and Ansible
• Part 21: EtherChannel, link aggregation with LACP, PAgP, and load balancing
• Part 22: Wireless LAN, 802.11 standards, WLC, CAPWAP, SSIDs, and WPA2/WPA3
• Part 23: First Hop Redundancy, HSRP, VRRP, and GLBP for gateway resilience
• Part 24: QoS, DSCP marking, LLQ, policing, and shaping for voice and video
• Part 25: Network Management, NTP, SNMPv3, syslog, CDP, and LLDP
• Part 26: Virtualization and Cloud, hypervisors, NFV, SDN, VPCs, and spine-leaf topology

System Design

• System Design, category overview
• Interview Framework, 4-step approach with time allocations, clarifying questions, and what interviewers score
• Back-of-Envelope Estimation, latency numbers, storage units, QPS formulas, worked examples
• Scalability, vertical vs horizontal scaling, stateless services, the scale cube
• Load Balancing, algorithms, L4 vs L7, health checks, sticky sessions
• Caching, cache-aside, read-through, write-through, eviction, CDN, invalidation
  • Redis, data structures, memory model, RDB vs AOF persistence, Sentinel vs Cluster
• Databases at Scale, SQL vs NoSQL trade-offs, sharding, replication, indexing
  • MySQL vs PostgreSQL, InnoDB vs heap storage, MVCC, WAL, index types, when to pick each
  • SpacetimeDB, WASM modules, reducers, subscription push model, trade-offs
• Message Queues, queue vs pub/sub, delivery guarantees, Kafka, RabbitMQ
  • Kafka, log segments, sequential writes, ISR replication, consumer groups, KRaft
• API Design, REST, GraphQL, gRPC, versioning, idempotency, pagination
• Rate Limiting, token bucket, leaky bucket, sliding window, where to enforce
• CAP Theorem, consistency vs availability under partition, PACELC
• Consistent Hashing, the ring, virtual nodes, minimal key remapping on resize
• Case Studies, end-to-end interview walkthroughs for six canonical systems
  • URL Shortener, ID generation, base62, redirect caching, analytics
  • Social Feed, fanout strategies, hybrid push/pull, celebrity problem
  • Video Streaming, chunked upload, transcoding, adaptive bitrate, CDN
  • Chat System, message ordering, WebSocket routing, exactly-once delivery
  • Notification System, multi-channel delivery, priority queues, deduplication
  • Ride Sharing, geospatial indexing, matching, real-time tracking, surge pricing
• Microservices vs Monolith, Conway’s Law, domain boundaries, modular monolith
• Circuit Breaker and Resilience, state machine, bulkhead, retry with jitter
• Event Sourcing and CQRS, append-only event log, projections, read/write model separation
• Distributed Locking, Redis SETNX, Redlock, ZooKeeper, fencing tokens
• Saga Pattern, choreography vs orchestration, compensating transactions

Web

• Web, category overview
• Django, 10-part series from beginner to expert
  • Part 1: Setup and MVT
  • Part 2: Models and the ORM
  • Part 3: Views, URLs, and templates
  • Part 4: Forms and user input
  • Part 5: Authentication
  • Part 6: DRF basics
  • Part 7: Advanced ORM
  • Part 8: Caching and performance
  • Part 9: Async, Channels, and Celery
  • Part 10: Production
• Express.js, 10-part series from setup and routing through production deployment
  • Part 1: Setup and routing
  • Part 2: Middleware
  • Part 3: Request and response
  • Part 4: REST API design
  • Part 5: Authentication
  • Part 6: Database integration
  • Part 7: Validation and error handling
  • Part 8: File uploads
  • Part 9: Testing
  • Part 10: Production

Testing

• Testing, category overview
• Test-Driven Development (TDD), red-green-refactor as a discipline
• Unit tests, fast, isolated, hundreds of them
• Component tests, the middle tier; UI rendering, DRF viewsets
• Integration tests, real databases, real message brokers, real wiring
• Smoke tests, the minimum-viable “is it alive?” checks
• Fuzz tests, property-based and coverage-guided fuzzing
• End-to-end tests (E2E), real browser, real backend, real user flow

Operations

• Ops, category overview
• Docker, the container runtime: images, containers, volumes, Compose, Dockerfile best practices
• Kubernetes, the container orchestrator: architecture, workloads, networking, storage, RBAC, autoscaling, footguns
  • Networking, pod network model, CNI, kube-proxy, CoreDNS, NetworkPolicy
  • Security Hardening, Pod Security Standards, admission controllers, RBAC lockdown, secrets
  • Troubleshooting, systematic debugging for every common failure mode
  • Workloads Reference, Deployment, StatefulSet, DaemonSet, Job, CronJob, probes, resource management
• Twelve-Factor Apps, the application-platform contract, all twelve canonical factors, current extensions, and runnable TypeScript, Python, and Go reference services
• Helm, the package manager for Kubernetes: charts, values, templates, releases
• Terraform, infrastructure as code: providers, resources, state, modules, multi-environment patterns
• n8n, workflow automation from beginner concepts through local Docker, cloud VM, n8n Cloud, queue mode, and Kubernetes hosting
• GitOps, Git as the source of truth for infrastructure, with a reconciliation agent doing the work
• ArgoCD, the reference GitOps controller for Kubernetes
• Gitflow, Vincent Driessen’s 2010 branching model and its modern alternatives
• MLOps, the engineering discipline around getting ML models into production
• Tokens, Keys, Secrets, and Environment Variables, what each credential type is, how they differ, where they live, and the mistakes that expose them

Cryptographic Systems

• Cryptographic Systems, category overview
• Distributed Cryptography, protocols that split keys and secrets across multiple parties so no single party holds the whole: secret sharing, MPC, threshold signatures, ZKPs, and distributed key generation
  • Secret Sharing, Shamir’s scheme and verifiable variants: split a secret into n shares, require any t to reconstruct
  • Multi-Party Computation, compute a function over distributed private inputs without revealing them
  • Threshold Signatures, sign with a t-of-n key where no party holds the full private key
  • Zero-Knowledge Proofs, prove a statement is true without revealing why
  • Distributed Key Generation, generate a shared keypair across n parties with no trusted dealer

Blockchain

• Blockchain, category overview
• Cryptocurrency, the major networks and assets
  • Bitcoin, UTXO model, SHA-256 PoW, 21M cap, Lightning Network, SegWit, and Taproot
  • Ethereum, the account model, EVM, gas, PoS (The Merge), ERC-20/721, L2 rollups, and MEV
  • Monero, ring signatures, stealth addresses, RingCT, and RandomX ASIC-resistant mining
  • Tether and Stablecoins, fiat-backed, crypto-collateralized, and algorithmic stablecoins and the UST/LUNA collapse
  • Wrapped Currencies, WBTC, wETH, and bridge protocols: lock-and-mint, bridge exploits, and IBC
  • Staking, Ethereum validator duties, slashing, inactivity leak, liquid staking (stETH/rETH), and restaking
• Consensus Mechanisms, how distributed nodes agree on the canonical chain
  • Proof-of-Work, SHA-256, Ethash, RandomX, ASIC mining, and 51% attacks
  • Proof-of-Stake, Casper FFG, LMD-GHOST, slashing, Ouroboros, and Tendermint
  • Delegated Proof-of-Stake, elected block producers, vote-trading failure modes, EOS and TRON
  • Byzantine Fault Tolerance, PBFT, Tendermint, HotStuff, and the safety-vs-liveness tradeoff
  • Proof-of-Authority, whitelisted validators, Clique, enterprise chains and Ethereum testnets
  • Proof-of-Space, disk storage as commitment, Chia’s plotting and farming, Proof-of-Time VDF
  • Other Consensus Mechanisms, Proof-of-History and broader comparisons

Conventions

• Topic: a folder with index.md. The overview/hub page.
• Subtopic (flat): <subtopic>.md inside the topic folder. Use for lightweight subtopics.
• Subtopic (folder): <subtopic>/index.md inside the topic folder. Use when the subtopic has images, code samples in files, or its own children.
• Depth: keep nesting to max 3 levels (category → topic → subtopic) for navigability.