Tech Refreshers

Brush up on the skills the market demands. Comprehensive quick-reference pages for experienced developers — dark-themed, syntax-highlighted, and designed for fast lookup. See what's trending on our Skills page.

41 refreshers
110,000+ lines
1,700+ code examples
Languages
Java 17+
Core language, collections, streams, concurrency, virtual threads, records, sealed classes, pattern matching
2,488 lines15 sections
Python 3 3.10+
Data model, typing, async/await, pattern matching, generators, testing, packaging, modern features
2,244 lines16 sections
JavaScript ES6+
Closures, prototypes, promises, async/await, modules, proxy, event loop, modern features through ES2025
2,949 lines15 sections
TypeScript 5.x
Type system, generics, utility types, discriminated unions, advanced patterns, and configuration for type-safe JavaScript
2,015 lines15 sections
Go 1.22+
Goroutines, channels, interfaces, generics, error handling, testing, context, common patterns
2,793 lines17 sections
C C17
Pointers, memory management, preprocessor, structs, concurrency, build systems, systems programming patterns
2,590 lines17 sections
C++ C++20/23
RAII, move semantics, templates, concepts, ranges, coroutines, smart pointers, concurrency, modern features
2,632 lines20 sections
Rust 2021+
Ownership, borrowing, lifetimes, traits, async/await, macros, smart pointers, concurrency, error handling
2,510 lines20 sections
Data Infrastructure
Apache Spark PySpark + Scala
DataFrames, Spark SQL, joins, shuffles, structured streaming, caching, performance tuning
2,251 lines13 sections
Apache Kafka Streams + Connect
Producers, consumers, exactly-once, Kafka Streams, Connect, Schema Registry, operations
1,930 lines12 sections
SQL Postgres + MySQL
Joins, window functions, CTEs, optimization, transactions, stored procedures, dialect differences
2,459 lines18 sections
Data Modeling OLTP + OLAP
Normalization, dimensional modeling, fact/dimension tables, SCDs, Data Vault, schema evolution, anti-patterns
2,174 lines20 sections
Apache Airflow 2.10+
DAGs, operators, TaskFlow API, scheduling, XComs, connections, executors, production patterns, ETL/ML pipelines
2,186 lines13 sections
Redis 7.x
Data structures, caching, pub/sub, streams, Lua scripting, clustering, production use cases (rate limiting, sessions, leaderboards)
2,370 lines15 sections
Lakehouse & Table Formats Delta + Iceberg + Hudi
Open table formats, ACID on object storage, time travel, schema/partition evolution, MERGE patterns, medallion architecture, MLOps on lakehouse, local setup, Databricks & AWS production
3,476 lines18 sections
Data Transform dbt + Spark + Flink + cuDF
dbt models, Spark DataFrames, Flink streams, NVIDIA cuDF GPU acceleration, comparison framework, and modern ELT patterns
2,450 lines19 sections
AI & Machine Learning
Machine Learning Ng + fast.ai
Linear/logistic regression, gradient descent, regularization, SVMs, trees, ensembles, k-means, PCA, ML strategy, production pipelines
1,493 lines12 sections
Deep Learning Ng + fast.ai
Backprop, activations, initialization, Adam, dropout, batch norm, CNNs, ResNet, RNNs, LSTMs, transfer learning, generative models
1,499 lines12 sections
PyTorch 2.x
Tensors, autograd, nn.Module, training loops, CNNs, data loading, saving/loading, TorchScript, deployment
2,120 lines13 sections
LLMs & Transformers GPT + BERT
Attention, transformer architecture, tokenization, fine-tuning, RLHF, prompting, RAG, embeddings, agents, evaluation
2,297 lines15 sections
Agentic Workflows Patterns + Frameworks
First-principles agent design, reflection, tool use, planning, multi-agent patterns, real use cases, and framework comparison
2,972 lines17 sections
Prompt Engineering Basics to Agentic
System prompts, structured output, few-shot, chain-of-thought, voice/realtime models, prompt chaining, safety, evaluation, and agentic patterns
2,181 lines17 sections
Accelerated Computing NVIDIA + CUDA
GPU vs CPU, CUDA model, practical scenarios (data, ML, LLM inference, vector search), NVIDIA stack, cost analysis, and getting started
2,778 lines17 sections
Frameworks
Spring Boot 3.x + Spring 6
Auto-configuration, web MVC, Spring Data JPA, Security (JWT, OAuth2), testing slices, Actuator, caching, Kafka, WebFlux, deployment
3,174 lines18 sections
REST APIs Spring + FastAPI + Express
Resource modeling, pagination, auth, versioning, rate limiting, caching, file uploads, OpenAPI, testing, security — production patterns in Java, Python, and Node
3,077 lines16 sections
Software Engineering
Design Patterns GoF + Modern
Creational, structural, behavioral patterns, plus modern architectural patterns (CQRS, Event Sourcing, Circuit Breaker), concurrency, anti-patterns
1,699 lines8 sections
DSA & LeetCode Patterns
Arrays, trees, graphs, DP, backtracking, greedy, tries, bit manipulation, shortest path, union-find, interview strategy
3,676 lines20 sections
Distributed Systems Consensus + Scale
Consensus, replication, partitioning, CAP/PACELC, consistency models, Raft, Saga, CDC, event sourcing, observability, data engineering patterns
2,048 lines17 sections
System Design Principal Engineer
Architecture decisions, database selection, caching, scaling, reliability, data pipelines, ML systems, API design, migration strategies
1,612 lines16 sections
Security
Application Security OAuth + OWASP
Scenario-driven: OAuth 2.0, JWT, OWASP Top 10, threat modeling, auth patterns, API security, incident response — follow a SaaS app from deploy to hardened
2,863 lines18 sections
DevOps & Infrastructure
Docker Compose + BuildKit
Images, containers, Compose, networking, volumes, multi-stage builds, security, production patterns
2,137 lines17 sections
Kubernetes K8s + Helm
Pods, deployments, services, networking, storage, RBAC, scaling, Helm, debugging, operators
2,896 lines18 sections
AWS Core Services
IAM, EC2, Lambda, S3, DynamoDB, VPC, SQS/SNS, ECS, CloudWatch, CloudFormation, architecture patterns
2,199 lines13 sections
Terraform IaC
HCL, providers, state management, modules, expressions, workspaces, testing, CI/CD, production patterns
2,046 lines13 sections
CI/CD GitHub Actions + GitLab CI
Pipelines, triggers, secrets, caching, artifacts, matrix builds, Docker in CI, deployments, reusable workflows, monorepos, security
1,976 lines13 sections
Networking TCP/IP + HTTP + TLS
TCP/IP, DNS, HTTP/2/3, TLS, REST, gRPC, internal vs external API exposure, load balancing, WebSockets, debugging, network security
1,928 lines14 sections
Linux Sysadmin + Shell
Shell commands, filesystem, permissions, processes, systemd, networking, SSH, storage, package management, performance monitoring
2,852 lines17 sections
Observability Prometheus + Grafana + OTel
Logs, metrics, traces, alerting, dashboards, SLOs, error budgets, data engineering & MLOps observability, full local Docker stack
2,803 lines16 sections
Build Tools & Version Control
Maven Build
POM, lifecycle, dependencies, plugins, profiles, multi-module projects, repositories
2,561 lines15 sections
Bazel Build
Starlark, hermetic builds, bzlmod, custom rules, remote caching, query language, CI/CD
2,321 lines15 sections
Git VCS
Branching, merging, rebasing, remotes, stashing, undoing, worktrees, hooks, workflows, internals
2,185 lines17 sections