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83 guides across 14 topics

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How the web works, explained plainly: DNS, HTTP, security headers, APIs, performance and software design, with links to the tools that check them.

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DNSHTTPSAPIs301 vs 302CI/CDCore Web VitalsA-Z glossary

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  • NetworkingHow data gets from one device to another: IP addresses and subnets, ports, NAT and DHCP, routing, TCP, UDP, QUIC and WebSockets.10
  • DNS & DomainsHow domain names resolve: record types, nameservers, TTLs and caching, DNSSEC, encrypted DNS, and the SPF, DKIM and DMARC records behind email.9
  • HTTP & The WebHow browsers and servers talk: requests and responses, status codes, headers, redirects and soft 404s.8
  • TLS & Web SecurityHTTPS and certificates, security headers, CORS, cookies, common attacks, trust scores and MCP security, with what each protects against and what it doesn’t.13
  • Software EngineeringDesign principles, architecture, dependency injection, concurrency, queues and testing, with trade-offs rather than rules.8
  • Web DevelopmentHow browsers are built and how they turn HTML, CSS and JavaScript into a page.1
  • APIsDesigning and consuming APIs: REST conventions, authentication, rate limits, webhooks, OpenAPI breaking changes and MCP transports.10
  • Git & WorkflowEveryday Git: the working tree, commits, branches, merging and rebasing, pull requests and undoing mistakes.1
  • DatabasesWhat databases do: relational, document and key-value stores, transactions, indexes and how to choose one.1
  • DevOps & InfraCI/CD pipelines, containers, Kubernetes, reverse proxies, load balancers and CDN caching.6
  • Cloud & EdgeWhere code runs: regions and availability zones, origin servers and edge functions, and what belongs where.1
  • PerformanceMaking pages load faster: Core Web Vitals, compression, caching, images and render-blocking resources.5
  • Monitoring & ReliabilityKnowing when something breaks: uptime checks, logs, metrics and traces, SLOs and error budgets, and incident response.5
  • Technical SEOThe technical side of search: crawling, robots.txt, XML sitemaps, broken links and a technical SEO checklist.5

Learning paths

Beginner

Networking fundamentals

Packet routing, ports, DNS resolution, and how TCP and UDP carry data.

  1. How the internet works: from your device to a website
  2. IPv4 vs IPv6: how IP addresses work
  3. TCP vs UDP: differences and when to use each
  4. What is a network port? Port numbers explained
  5. What is DNS? How the Domain Name System works
Start this path
Intermediate

Web security and encryption

HTTPS handshakes, certificates, CORS, and the most common web attacks.

  1. How HTTPS works: TLS handshake, keys and encryption
  2. SSL certificates: validation, chains and common errors
  3. Same-origin policy and CORS: how cross-origin reads work
  4. XSS, CSRF and SSRF: how they work and how to prevent them
Start this path
Intermediate

Software architecture

SOLID, clean code, dependency injection, and modular system design.

  1. SOLID principles explained, with practical examples
  2. DRY, KISS and YAGNI: clean code principles in practice
  3. Dependency injection explained, with TypeScript examples
  4. Clean architecture: the dependency rule, ports and adapters
Start this path

Start with these

Networking · 4 min readHow the internet works: from your device to a websiteThe internet is thousands of independent networks joined by IP. How packets, routing, DNS, TCP or QUIC, TLS and HTTP combine to load one web page.Read guide DNS & Domains · 4 min readWhat is DNS? How the Domain Name System worksDNS turns domain names into IP addresses and other records. How resolvers, nameservers, records and caching fit together, and what fails when DNS breaks.Read guide HTTP & The Web · 3 min readHow HTTP works: the life of one requestWhat happens between typing a URL and seeing the page: DNS lookup, connection, TLS, request and response, and how HTTP/1.1, HTTP/2 and HTTP/3 differ.Read guide

All guides

83 guides

  • Cloud & Edge · 4 min readCloud vs edge computing: where your code should runWhere code runs in the cloud and at the edge: regions, availability zones and origin servers, what edge functions can and cannot do, and how to choose.intermediate
  • DevOps & Infra · 5 min readCI/CD pipeline stages: from commit to productionHow a CI/CD pipeline is put together: build, test and security stages, one artifact promoted through environments, approvals, rollbacks and secrets.intermediate
  • Databases · 5 min readWhat is a database? SQL, NoSQL, ACID and indexesWhat a database adds beyond files, how relational, document and key-value stores differ, what ACID transactions mean and why indexes make queries fast.beginner
  • Web Development · 4 min readBrowser architecture and the critical rendering pathHow a browser is split into processes and engines, and the steps from HTML bytes to first paint, including render-blocking CSS and parser-blocking scripts.intermediate
  • Git & Workflow · 5 min readGit basics: staging, commits, branches and undoing mistakesHow Git's working tree, staging area and commits fit together, why branches are pointers, merge vs rebase, a pull request workflow and how to undo mistakes.beginner
  • Networking · 4 min readHow the internet works: from your device to a websiteThe internet is thousands of independent networks joined by IP. How packets, routing, DNS, TCP or QUIC, TLS and HTTP combine to load one web page.beginner
  • Networking · 4 min readOSI model: what each of the seven layers doesThe seven OSI layers, what each one handles with real protocol examples, how the TCP/IP model maps to them, and why layer numbers help with troubleshooting.beginner
  • Networking · 4 min readTCP vs UDP: differences and when to use eachTCP delivers a reliable, ordered byte stream after a handshake; UDP sends independent datagrams with no setup. How they differ and which protocols use each.intermediate
  • Networking · 4 min readIPv4 vs IPv6: how IP addresses workIPv4 addresses are 32 bits and IPv6 addresses are 128 bits. How each is written, which ranges are private, why IPv4 ran out, and how dual stack works.beginner
  • Networking · 4 min readSubnetting and CIDR notation, with worked examplesHow a CIDR prefix such as /24 splits an IP address into network and host bits, how many addresses it holds, and worked IPv4 and IPv6 subnet examples.intermediate
  • Networking · 4 min readWhat is a network port? Port numbers explainedA port is a 16-bit number that tells a host which program should receive traffic. Port ranges, common ports such as 22, 53 and 443, and how firewalls use them.beginner
  • Networking · 4 min readNAT and DHCP: how devices on your network get onlineDHCP gives each device an address, gateway and DNS servers, and NAT shares one public IPv4 address among them. How both work and why NAT blocks inbound traffic.intermediate
  • Networking · 4 min readRouting vs switching: how routers and switches differSwitches forward frames by MAC address inside one network; routers forward packets between networks by IP address. How each decides, plus ARP, gateways and BGP.intermediate
  • Networking · 5 min readWebSockets explained: the handshake, uses and limitsA WebSocket upgrades one HTTP request into a two-way message channel. How the handshake works, when to pick SSE or polling instead, and proxy and auth caveats.intermediate
  • Networking · 4 min readQUIC and HTTP/3: how the UDP-based transport worksQUIC is a transport protocol over UDP with TLS 1.3 built in, and HTTP/3 runs on it. Why it exists, 0-RTT and its replay risk, migration and HTTP/3 discovery.advanced
  • DNS & Domains · 4 min readWhat is DNS? How the Domain Name System worksDNS turns domain names into IP addresses and other records. How resolvers, nameservers, records and caching fit together, and what fails when DNS breaks.beginner
  • DNS & Domains · 4 min readHow DNS resolution works, step by stepThe path of one DNS lookup through browser and OS caches, a recursive resolver, and root, TLD and authoritative servers, and how to watch it with dig +trace.intermediate
  • DNS & Domains · 4 min readDNS record types explained: A, CNAME, MX, TXT and moreWhat A, AAAA, CNAME, MX, TXT, NS, SOA, CAA, SRV, PTR and HTTPS records do. Each comes with a zone file example, and the CNAME rule is stated exactly.beginner
  • DNS & Domains · 4 min readDNS TTL and caching: why DNS changes take timeHow DNS TTL controls caching, why DNS propagation means waiting for caches to expire, how to lower the TTL before a change, and how negative answers are cached.intermediate
  • DNS & Domains · 4 min readWhat is DNSSEC? How DNS signatures work and failDNSSEC signs DNS records so resolvers can detect forged answers. What it protects, how DNSKEY, RRSIG and DS form a chain of trust, and why it causes SERVFAIL.advanced
  • DNS & Domains · 3 min readDNS over HTTPS vs DNS over TLS: what each one hidesDoH and DoT both encrypt DNS between your device and a resolver. How they differ, what they hide, what they still reveal, and the network-filtering trade-off.intermediate
  • DNS & Domains · 4 min readDomain name structure: registries, registrars and DNS hostsHow domain names are built from labels, what the registry, registrar and DNS host each do, how delegation works, and why a CNAME cannot sit at the apex.beginner
  • DNS & Domains · 4 min readHow to troubleshoot DNS: NXDOMAIN, SERVFAIL and moreDiagnose DNS problems by response code: causes and fixes for NXDOMAIN, SERVFAIL, REFUSED and stale answers, with the dig and nslookup commands to run.intermediate
  • DNS & Domains · 5 min readSPF, DKIM and DMARC: how email authentication worksWhat SPF, DKIM and DMARC each prove, how DMARC alignment ties them to the visible From address, example records, and a safe order to roll them out.intermediate
  • HTTP & The Web · 3 min readHow HTTP works: the life of one requestWhat happens between typing a URL and seeing the page: DNS lookup, connection, TLS, request and response, and how HTTP/1.1, HTTP/2 and HTTP/3 differ.beginner
  • HTTP & The Web · 4 min readHTTP request anatomy: request line, headers and bodyWhat each part of an HTTP request does: the request line, the headers that matter most, the body, and which methods are safe or idempotent.intermediate
  • HTTP & The Web · 3 min readHTTP response anatomy: status line, headers and bodyHow to read an HTTP response: the status line, headers such as Content-Type, Cache-Control, ETag and Set-Cookie, the body, and raw headers with curl.intermediate
  • HTTP & The Web · 5 min readHTTP status codes: what each one means and what to doHTTP status codes by class, from 200 and 301 to 404, 429 and 503. Each entry says what the code means and what to do when you see it.beginner
  • HTTP & The Web · 3 min readWhat is a redirect? Server, meta refresh and JavaScriptA redirect sends a browser or crawler from one URL to another. How 3xx, meta refresh and JavaScript redirects work, when to use each and what they cost.beginner
  • HTTP & The Web · 3 min read301 vs 302 redirects: which to use, plus 307 and 308A 301 is a permanent redirect and a 302 a temporary one. How 307 and 308 differ, how browsers cache each code and how search engines read them.beginner
  • HTTP & The Web · 4 min readRedirect chains and loops: how to find and fix themA redirect chain is two or more redirects in a row before the final page. What causes chains and loops, what they cost, and how to find and flatten them.intermediate
  • HTTP & The Web · 4 min readSoft 404 errors: what they are and how to fix themA soft 404 is a missing page that returns 200 OK instead of 404. What causes them, how to detect them with curl and Search Console, and how to fix them.intermediate
  • TLS & Web Security · 3 min readHow HTTPS works: TLS handshake, keys and encryptionHow HTTPS uses TLS 1.3 to authenticate the server and encrypt traffic, step by step, and what HTTPS and the padlock do not protect you from.beginner
  • TLS & Web Security · 4 min readSSL certificates: validation, chains and common errorsWhat an SSL/TLS certificate contains, how DV, OV and EV differ, why the chain matters, and how to fix expired, mismatched or incomplete certificates.beginner
  • TLS & Web Security · 3 min readHow website trust scores work and what they missHow technical trust scores turn HTTPS, redirect, header and URL signals into a number, how Website Trust Inspector scores a site, and what no score can show.beginner
  • TLS & Web Security · 3 min readSame-origin policy and CORS: how cross-origin reads workWhat counts as an origin, what the same-origin policy blocks, how CORS headers and preflight requests relax it, and why CORS is not server-side access control.intermediate
  • TLS & Web Security · 4 min readXSS, CSRF and SSRF: how they work and how to prevent themHow cross-site scripting, cross-site request forgery and server-side request forgery work, and the specific defenses that stop each one in a web application.advanced
  • TLS & Web Security · 3 min readZero trust security: principles and where to startWhat zero trust means in practice: verify every request explicitly, grant least privilege and assume breach, plus first steps and what it does not promise.intermediate
  • Software Engineering · 5 min readSOLID principles explained, with practical examplesWhat each of the five SOLID principles means, the change problem it addresses, a short example of each, and when applying them rigidly makes code worse.intermediate
  • Software Engineering · 4 min readDRY, KISS and YAGNI: clean code principles in practiceWhat DRY, KISS and YAGNI mean, why DRY is about knowledge rather than similar code, how naming helps, and when an abstraction costs more than duplication.beginner
  • Software Engineering · 4 min readDependency injection explained, with TypeScript examplesWhat dependency injection is, how constructor injection works in TypeScript, how it relates to IoC and DI containers, and when a function argument is enough.intermediate
  • Software Engineering · 4 min readClean architecture: the dependency rule, ports and adaptersHow clean architecture keeps business rules free of frameworks: the dependency rule, use cases, ports and adapters, folder layout and when it is overkill.advanced
  • Software Engineering · 4 min readMonolith vs microservices: trade-offs and when to splitHow monoliths and microservices differ in deployment, data ownership, teams and operating cost, why a modular monolith is a middle path, and when to split.intermediate
  • Software Engineering · 5 min readRace conditions: causes, examples and how to prevent themWhat a race condition is, concurrency vs parallelism, a lost-update example, and the fixes: atomic updates, locks, isolation levels and idempotency keys.advanced
  • Software Engineering · 5 min readMessage queues and event-driven architecture explainedQueues vs pub/sub, why at-least-once delivery needs idempotent consumers, how ordering, retries and dead-letter queues work, and when to avoid events.intermediate
  • Software Engineering · 4 min readThe test pyramid: unit, integration and end-to-end testsWhat the test pyramid recommends and why, how unit, integration and end-to-end tests differ, what makes tests flaky, and which tests to automate in CI first.beginner
  • APIs · 3 min readWhat is an API? Definition, examples and how it worksAn API is a defined way for one program to ask another for data or actions. See web and library examples, how API contracts work, and why versions matter.beginner
  • APIs · 5 min readREST API design principles: URLs, methods and errorsHow REST APIs name resources, use HTTP methods safely, return status codes and RFC 9457 errors, stay stateless, paginate results and handle versioning.intermediate
  • APIs · 5 min readAPI authentication: API keys vs OAuth 2.0 vs JWTAPI keys identify an app, OAuth 2.0 issues scoped tokens, and a JWT is a token format. When to use each, how to validate a JWT, and where to store tokens.advanced
  • APIs · 4 min readAPI rate limiting: algorithms, 429 and Retry-AfterWhy APIs limit request rates, how fixed window, sliding window, token bucket and leaky bucket compare, and how clients should handle 429 and Retry-After.intermediate
  • APIs · 4 min readWebhooks explained: signatures, retries and idempotencyHow webhooks deliver events over HTTP, how to verify HMAC signatures and block replays, and how to handle retries, duplicates and the choice versus polling.intermediate
  • DevOps & Infra · 4 min readWhat is CI/CD? Integration, delivery and deploymentWhat continuous integration, continuous delivery and continuous deployment each mean, what each one requires, and why small, frequent changes are safer.beginner
  • DevOps & Infra · 4 min readWhat is a Docker container? Images, layers and DockerfilesWhat a container is and how it differs from a virtual machine, how images and layers work, a small production Dockerfile, and rules for clean images.intermediate
  • DevOps & Infra · 5 min readKubernetes concepts: Pods, Deployments and ServicesThe core Kubernetes objects and how they fit together, how desired state, rolling updates and health probes work, and when Kubernetes is more than you need.intermediate
  • DevOps & Infra · 5 min readReverse proxy vs load balancer: what each one doesWhat a reverse proxy does, how layer 4 and layer 7 load balancing differ, common algorithms and health checks, and why X-Forwarded-For needs care.intermediate
  • DevOps & Infra · 4 min readHow CDN caching works: cache keys, hits and purgesHow a CDN decides what to store and for how long: cache keys, s-maxage, hits and misses, revalidation, purging, the Vary header and what to keep off it.intermediate
  • Performance · 5 min readCore Web Vitals: what LCP, INP and CLS measureWhat LCP, INP and CLS measure, the "good" limits at the 75th percentile, field versus lab data, and the usual causes and fixes for each metric.beginner
  • Performance · 4 min readBrowser rendering: style, layout, paint and compositeWhat the browser does for each frame, which CSS and DOM changes trigger layout or paint, why layout thrashing is slow, and how long tasks drop frames.advanced
  • Performance · 4 min readHTTP caching headers: Cache-Control, ETag and 304sHow Cache-Control directives, ETag and Last-Modified validators and 304 responses work, plus sensible headers for HTML pages and hashed static assets.intermediate
  • Performance · 4 min readOptimizing web assets: images, fonts, JavaScript and CSSHow to shrink and load images, fonts, JavaScript, CSS and third-party scripts: modern formats, lazy loading, font-display, code splitting and Brotli.intermediate
  • Performance · 4 min readWeb performance metrics: TTFB, FCP, Speed Index and TBTWhat TTFB, First Contentful Paint, Speed Index, Total Blocking Time, page weight and request count tell you, and why to track the 75th percentile.beginner
  • Monitoring & Reliability · 3 min readUptime monitoring: what it measures and how checks workWhat uptime monitoring measures, the main check types (HTTP, keyword, TCP, DNS and certificate expiry), check frequency, confirming failures and routing alerts.beginner
  • Monitoring & Reliability · 4 min readLogs, metrics and traces: what each one tells youLogs, metrics and traces answer different questions about a running system. How each works, how trace IDs connect them, and what each costs to collect and keep.intermediate
  • Monitoring & Reliability · 3 min readSLIs, SLOs and SLAs explained, with error budgetsSLIs, SLOs and SLAs defined with examples, how to pick an SLI, error budget math (99.9% over 30 days allows 43.2 minutes) and what an SLA adds.intermediate
  • Monitoring & Reliability · 3 min readIncident management: roles, updates and blameless reviewsHow to run an incident from detection to review: severity levels, the incident commander and other roles, updates for users, timelines and blameless follow-ups.intermediate
  • Monitoring & Reliability · 3 min readHow to monitor website uptime, step by stepSet up website uptime monitoring: choose the URLs that matter, use an always-on monitoring service, set intervals, thresholds and alerts, and plan maintenance.beginner
  • Technical SEO · 4 min readHow to find broken links on your websiteFind broken links by crawling your internal pages, checking external links in bulk, sorting failures by cause, re-checking the uncertain ones and fixing each.beginner
  • Technical SEO · 4 min readTechnical SEO checklist: crawl, index and page basicsA working technical SEO checklist: robots.txt access, noindex and canonicals, status codes, redirects, sitemaps, titles, internal links, HTTPS and page weight.beginner
  • Technical SEO · 4 min readWebsite crawling explained: how crawlers find pagesHow a web crawler works: seed URLs, fetching, link extraction, the frontier, depth and page limits, robots.txt, politeness, JavaScript and crawl reports.beginner
  • Technical SEO · 3 min readXML sitemaps: format, limits and what to includeWhat an XML sitemap does and doesn't do, its format and size limits, how sitemap index files work, where to declare it, and which URLs belong in it.beginner
  • Technical SEO · 4 min readrobots.txt rules: syntax, matching and common mistakesHow robots.txt works under RFC 9309: User-agent, Disallow, Allow and Sitemap lines, wildcard matching, why it can't hide pages from search, and where it lives.intermediate
  • TLS & Web Security · 3 min readHTTP security headers: which to send and whyWhich HTTP security headers to send, what CSP, HSTS, nosniff, framing, Referrer-Policy, Permissions-Policy and COOP prevent, and which old headers to drop.intermediate
  • TLS & Web Security · 4 min readContent Security Policy (CSP): directives and rolloutHow to write a Content-Security-Policy: the directives that matter, nonces, hashes and strict-dynamic, report-only rollout, and mistakes that weaken a policy.advanced
  • TLS & Web Security · 3 min readWhat is HSTS? Strict-Transport-Security and preloadHow the Strict-Transport-Security header forces HTTPS, what it prevents, the first-visit gap, preload list requirements and the risk of preloading too early.beginner
  • TLS & Web Security · 3 min readCookie security: Secure, HttpOnly and SameSite explainedWhat Secure, HttpOnly and SameSite cookie attributes do, how __Host- and __Secure- prefixes and Domain and Path scope work, and safe session cookie settings.intermediate
  • APIs · 3 min readOpenAPI breaking changes: what breaks API clientsWhich OpenAPI contract changes break existing clients, from removed fields to new security requirements, which are usually safe, and how to ship a break.intermediate
  • APIs · 3 min readRequest vs response schema compatibility in APIsWhy tightening a request schema breaks clients while tightening a response is usually safe, with examples for required fields, nulls, enums and types.advanced
  • APIs · 3 min readHow enum changes break API clients and generated SDKsAdding an enum value can break clients that read it, and removing one breaks clients that send it. Why generated SDKs fail and how to plan for new values.intermediate
  • APIs · 3 min readOpenAPI 3.0 vs 3.1: differences and migration checklistWhat changed in OpenAPI 3.1, from JSON Schema 2020-12 compatibility and type arrays to webhooks, plus a checklist for migrating a 3.0 document.intermediate
  • TLS & Web Security · 4 min readMCP security: tools, prompt injection and least privilegeHow MCP connects AI apps to tools and data, where its trust boundaries sit, and how prompt injection, broad permissions and risky tool pairs cause harm.intermediate
  • TLS & Web Security · 4 min readMCP authorization and why token passthrough is forbiddenHow remote MCP servers use OAuth 2.1, why each token must be issued for one specific server, and why forwarding a client's token to another API is banned.advanced
  • TLS & Web Security · 3 min readMCP tool annotations: what the hints mean and their limitsWhat MCP tool annotations such as readOnlyHint and destructiveHint declare, why clients must treat them as untrusted hints, and how to use them in approvals.intermediate
  • APIs · 4 min readMCP stdio vs Streamable HTTP: transport security comparedHow MCP's stdio and Streamable HTTP transports differ, the main risks of each, from unpinned npx packages to DNS rebinding, and how to choose between them.intermediate

Try it in a tool

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  • URL Intelligence PlatformCheck links in bulk, trace redirects, and crawl a site for broken pages
  • DNS LookupLook up DNS records and check how a domain is set up
  • Website Trust InspectorLook at the technical signals behind a website before you trust it
  • API Payload DiffCompare two JSON or XML responses and see what actually changed
  • AI-Generated Code Risk ScannerCheck AI-written or copied code for leaked secrets and risky patterns
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