Learn library
Software engineering guides and courses
The SevyDevy Learn library has free, in-depth guides on system design, backend, AI engineering, frontend and DSA, and free courses taught lesson by lesson. Every guide starts with a short answer, explains the why with diagrams and tables, and ends with the questions interviewers ask, so you can practise it next.
476 guides · 2 courses · 6 topics
Updated · Written by the SevyDevy team
Browse by topic
System design
Real systems, from rate limiters and distributed systems to data infrastructure.
124 guidesAI and GenAI
RAG, vector databases, LLM serving, MCP and how AI systems run in production.
159 guidesBackend
Backend, databases, networking, caching and queues from first principles, plus incidents explained.
115 guidesFrontend
React, Next.js, TypeScript and machine coding rounds.
56 guidesDSA
The core patterns behind coding interview questions.
1 guideInterview prep
How interviews work now and how to prepare for them.
21 guides
Start here
New to a topic? Read one of these first.
System Design for Beginners: A Visual Roadmap from Requirements to Real Systems
A practical visual guide to system design for beginners, covering requirements, APIs, data modeling, architecture, scaling, reliability, observability, and real-world examples.
Read the guide · 22 minBackend Engineering from First Principles
A detailed guide to backend engineering from first principles. Learn how backend systems really work beyond CRUD APIs, including requests, HTTP, routing, authentication, validation, business logic, databases, caching, queues, observability, security, scaling, testing, OpenAPI, webhooks, and DevOps.
Read the guide · 18 minIntroduction to GenAI System Design: How AI Systems Actually Work in Production
A practical deep dive into GenAI system design covering LLMs, RAG, cost optimization, latency trade-offs, and real-world architecture patterns.
Read the guide · 15 minHow to Use DSA’s 25 Core Patterns: A Visual Guide with Creative Diagrams and Detailed Explanations
A detailed visual guide to the 25 core DSA patterns, covering how to identify them, when to use them, how they connect, and how to think like an interviewer using creative diagrams.
Read the guide · 20 min
Courses
Original lessons that teach one subject from scratch, in order like a book.
- Free · GenAI · Beginner
GenAI from Scratch
8 modules · 32 lessons · 5½ hoursWhat you will be able to doExplain how AI chat apps really work, write prompts that land, and sketch a real AI product with RAG and agents.Starts with: What is generative AI?Video lessons · Coming soonStart the course - Free · System design · Beginner to intermediate
System Design from Scratch
8 modules · 35 lessons · 7 hoursWhat you will be able to doTake an app from one server to millions of users, explain every part you add, and sketch the design out loud.Starts with: What is system design? Seeing the whole app behind one tapVideo lessons · Coming soonSee the course - Coming soon · Frontend
Frontend machine coding
What you will be able to doBuild common UI components cleanly in a timed round, with state, accessibility and tests. - Coming soon · DSA
DSA patterns
What you will be able to doSpot which core pattern a coding question needs and solve it step by step, then explain the complexity.
All guides
Newest first. Search or pick a topic.
476 guides, newest first
- How SSH Works: Key Exchange, Host Keys, Channels and Agent ForwardingBackend · A plain-English guide to how SSH works: key exchange, host keys and known_hosts, public-key login, channels and tunnels, and why ProxyJump beats agent forwarding, shown on one running example of a laptop reaching a private app server through a bastion.25 min read · Updated 3 Nov 2026
- First 90 Days as a Software Engineer: Questions, Owners and a 30-60-90 PlanInterview prep · A plain-English guide to your first 90 days as a software engineer: early wins vs deep ramp-up, a question budget, finding real code owners with CODEOWNERS and git history, on-call shadowing and a 30-60-90 plan, shown on one running example of a refunds team.22 min read · Updated 2 Nov 2026
- Authlib's October 2026 Vulnerability Explained: When No Signature Meant ValidBackend · A plain-English guide to the Authlib vulnerability CVE-2026-96760 and its sibling key bugs: why an empty signature list passed, who is affected and how to upgrade to 1.9.1, shown on one running example of a service that checks signed partner messages.22 min read · Updated 1 Nov 2026
- Faceted Search Explained: Filter URLs, Honest Counts and the Back ButtonFrontend · A plain-English guide to faceted search on the front end: filters in the URL, pushState vs replaceState, popstate, honest facet counts and zero-result rules, shown on one running example of a small shoe shop.22 min read · Updated 1 Nov 2026
- Linux's October 2026 TCP Use-After-Free Explained: How to Patch CVE-2026-98432Backend · A plain-English guide to CVE-2026-98432, the Linux IPv4 TCP use-after-free fixed in October 2026: how the handshake race works, which kernels are fixed and how to patch, shown on one running example of a 40-server fleet.20 min read · Updated 1 Nov 2026
- Node-Forge's October 2026 Vulnerability Explained: When a Leaf Acts as a CABackend · A plain-English guide to the node-forge vulnerability of October 2026: how retired extension IDs let a leaf certificate act as a CA, why zero-round PKCS#12 files passed any password, and how to upgrade to 1.4.2, shown on one running example of a smart meter gateway.23 min read · Updated 1 Nov 2026
- OAuthLib's October 2026 Vulnerability Explained: Scopes for the Wrong ClientBackend · A plain-English guide to the OAuthLib vulnerability fixed in 4.0.0: how token grants checked the wrong client, who is exposed, and how to upgrade to 4.0.1 safely, shown on one running example of an internal payments login server.19 min read · Updated 1 Nov 2026
- Pyasn1's October 2026 Vulnerability Explained: Why Decoding Went QuadraticBackend · A plain-English guide to the pyasn1 vulnerability fixed in 0.6.5: what quadratic-time decoding is, which packages pull pyasn1 in and how to upgrade and verify, shown on one running example of a certificate upload tool.21 min read · Updated 1 Nov 2026
- PyTorch 2.15 Explained: What Breaks When You Upgrade and How to Fix ItAI and GenAI · A plain-English guide to PyTorch 2.15: the Python 3.10 cut-off, nested-tensor checkpoints, the rewritten NCCL backend and the smaller changes that fail tests, shown on one running example of a nightly text-classifier training job.18 min read · Updated 1 Nov 2026
- Tornado's October 2026 Security Update Explained: Keep the Event Loop FreeBackend · A plain-English guide to the Tornado security update: what Tornado 6.6 fixes, why one request could freeze a server, and how to upgrade safely, shown on one running example of a live dashboard served by Tornado.21 min read · Updated 1 Nov 2026
- Contextual Retrieval Explained: Chunk Context, Index Cost and RecallAI and GenAI · A plain-English guide to contextual retrieval: why chunks lose meaning when split, how a short context line helps BM25 and embedding search, what it costs at index time and which cheaper fixes to try first, shown on one running example of an insurance helpdesk bot.24 min read · Updated 31 Oct 2026
- API Key Management Explained: Formats, Hashing, Rotation and LeaksBackend · A plain-English guide to API key management: how to format, store, scope, rotate and revoke the keys your API gives customers, shown on one running example of a small invoicing API.25 min read · Updated 30 Oct 2026
- MuPDF's October 2026 PDF Encryption Flaw Explained: A 9-Bit AES KeyBackend · A plain-English guide to the PDF encryption vulnerability in MuPDF: why clock-seeded keys left AES-256 PDFs guessable, how to check your version and how to re-encrypt files, shown on one running example of a payslip service.15 min read · Updated 30 Oct 2026
- Auction System Design: Proxy Bids, Anti-Sniping and a Consistent Top BidSystem design · A plain-English guide to auction system design: proxy bids and increments, bid storms near the close, anti-sniping soft close, race-free top bids in PostgreSQL and Redis, and safe closing, shown on one running example of an online watch auction.30 min read · Updated 29 Oct 2026
- Bot Detection System Design: Signals, Risk Scores and Tiered ResponsesSystem design · A plain-English guide to bot detection system design: the signals worth collecting, how a risk score picks between allow, throttle, challenge and block, where fingerprinting meets privacy limits, and how to measure false positives, shown on one running example of a festive-sale signup and login flow.29 min read · Updated 29 Oct 2026
- Browser Code Editor Design: Piece Tables, Incremental Parsing and LSPFrontend · A plain-English guide to browser code editor design: why a textarea fails, how editors store text in piece tables and trees, re-parse only what changed, draw only visible lines and get language smarts from workers and LSP, shown on one running example of a coding-practice site's editor.28 min read · Updated 29 Oct 2026
- Dashboard Frontend Design: Frame Budgets, Live Updates and DownsamplingFrontend · A plain-English guide to dashboard frontend design: frame budgets, SVG vs canvas, push vs polling, requestAnimationFrame batching, LTTB and min-max downsampling, hidden tabs, resizing and accessible charts, shown on one running example of a live operations dashboard.32 min read · Updated 29 Oct 2026
- Facebook TAO Explained: Objects, Associations and Leader-Follower CachingSystem design · A plain-English guide to Facebook TAO: how objects and associations model the social graph, how leader and follower cache tiers sit over sharded MySQL and what eventual consistency cost, shown on one running example of a hostel wifi post and its comments.26 min read · Updated 29 Oct 2026
- Inngest's October 2026 Outages Explained: When Deadlines Drained the PoolBackend · A plain-English guide to the Inngest outage of October 2026: why short query deadlines made PgBouncer destroy database connections faster than it could replace them, shown on one running example of a job-scheduling service.19 min read · Updated 29 Oct 2026
- Mobile System Design Interview: Offline Sync, Battery and a 45-Minute PlanInterview prep · A plain-English guide to the mobile system design interview: offline-first storage, sync and conflicts, Android and iOS background limits, push, app size and rollouts, shown on one running example of a field sales order app.31 min read · Updated 29 Oct 2026
- Multi-LoRA Serving Explained: Batching Many Fine-Tunes on One Base ModelAI and GenAI · A plain-English guide to multi-LoRA serving: why one base model can carry many small adapters, how much memory each adapter needs, how one batch mixes adapters, and the vLLM limits that matter, shown on one running example of an edtech assistant for 100 coaching institutes.23 min read · Updated 29 Oct 2026
- Product Architecture Interview: User Journeys, APIs and Data ModelsInterview prep · A plain-English guide to the product architecture interview: how it differs from an infrastructure system design round, how to frame user journeys, answer API-first and model the data, and what interviewers score, shown on one running example of event invites and RSVPs.28 min read · Updated 29 Oct 2026
- State Space Models Explained: Linear-Time Sequences with a Fixed-Size StateAI and GenAI · A plain-English guide to state space models: the linear recurrence, discretisation, the convolution and recurrent views, selective updates, parallel scans, memory maths against a KV cache and the exact-recall limit, shown on one running example of a long-transcript summariser.27 min read · Updated 29 Oct 2026
- Terraform State Explained: Locking, Drift, Imports and RecoveryBackend · A plain-English guide to Terraform state: what the state file stores, why it leaks secrets, how backends, locking and drift checks work, and how to recover lost state, shown on one running example of a small online shop's infrastructure.29 min read · Updated 29 Oct 2026