Free DevOps Simulators

Type a cron expression and see the next runs as real dates and times, in any timezone. Why */7 is not every 7 minutes, why day-of-month and day-of-week are OR and not AND, what happens to a job scheduled in the hour daylight saving deletes, and which expressions never fire at all. The parser and the schedule are real and run in your browser.

Flip eight bits by hand and watch the number change, the way the wooden demonstrators in computing museums do it. Then switch modes and the same tiles become a chmod permission set and a subnet mask, so 755 and /26 stop being things to memorise. Count upward to watch a carry travel along the bits.

Visualize how the infamous :(){ :|:& };: fork bomb works. Watch processes multiply exponentially, exhaust system resources, and learn how to protect against it with ulimit, cgroups, and systemd.

Master essential Linux commands through interactive lessons. Practice pwd, ls, cd, cat, grep, chmod, pipes, and more in a simulated terminal environment with 6 progressive lessons.

Six real docker run commands, each carrying a flag that hands an attacker the host. Click the dangerous ones, then see the actual escape path and what to grant instead. Covers the Docker socket, --privileged, host PID namespace, SYS_ADMIN and unconfined AppArmor, plus one command with nothing wrong with it.

Watch what really happens when you run docker run -p 8080:80 nginx, one layer at a time. Step down the whole stack: the CLI, the daemon, the registry pull, containerd, the OCI runtime bundle, runc, the running container, and the shared Linux kernel. Every stage shows the real low-level command you can run yourself, so it doubles as a tour of the primitives that make a container: namespaces, cgroups, and runc. A container is not a small VM, and this shows you why.

Practice Docker commands in an interactive browser terminal. Learn images, containers, logs, exec, Dockerfile builds, volumes, networks, and Docker Compose with a live Docker daemon visualization.

Ask whether a service account can do a verb on a resource in a namespace, and get the reason rather than a yes or no. Covers the ClusterRole bound by a RoleBinding that is silently confined to one namespace, why resourceNames grants get but never list, the dangling roleRef that fails without an error, and the fact that RBAC has no deny rules. Every answer prints the matching kubectl auth can-i command. The engine is real and runs in your browser.

Visualize Kubernetes networking and CNI packet paths with an interactive simulator. Learn Pod-to-Pod routing, same-node and cross-node traffic, ClusterIP Services, EndpointSlices, headless Services, LoadBalancer, NodePort, kube-proxy, eBPF service routing, Ingress, NetworkPolicy, and internet egress.

Practice Kubernetes commands in an interactive browser terminal. Learn kubectl contexts, nodes, Pods, Deployments, Services, rollouts, logs, exec, events, ConfigMaps, and cleanup workflows with a live cluster visualization.

Visualize how service mesh proxies handle traffic between microservices. Learn mTLS, traffic splitting, retries, circuit breakers, and explore Istio and Linkerd patterns.

Drag-and-drop Pods onto Nodes while honoring kube scheduling rules: resources, taints/tolerations, selectors, and topology spread.

Resolve Git merge conflicts in a browser lab. Read the conflict markers and the three index stages, edit the file to what it should be, take a side with --ours or --theirs, see why they swap during a rebase, back out with git merge --abort, and catch a clean merge that breaks the build.

Practice Git in an interactive browser terminal with a visual repository model. Learn the working directory, staging area, local commits, branch pointers, remotes, fast-forward merges, fetch, and rebase.

Test your Git knowledge with interactive scenarios covering branches, merges, rebases, conflicts, and the recovery commands you reach for under pressure.

Edit YAML and watch what the parser actually decides your values are. The Norway problem where NO becomes the boolean false, version 1.10 becoming a lower number than 1.9, leading zeros meaning octal in one spec and decimal in another, empty against null against an empty string, block scalars, and tabs. Every document is read twice, under YAML 1.1 and YAML 1.2, so you can see exactly where the two specs disagree. The parser is real and runs in your browser.

See how a pull request becomes a temporary copy of your app, complete with a private URL, safe test data, review checks, and automatic cleanup.

Learn deployment strategies like Blue-Green, Canary, Rolling Updates, and Recreate. Visualize how each strategy handles traffic routing, downtime, and rollbacks.

Learn GitOps principles through interactive scenarios. Understand Git as source of truth, automated sync, and drift detection.

Take the page as incident commander. Direct two responders, read the evidence they bring back, choose a mitigation, keep customers updated, and confirm the recovery holds before you resolve. Turn-based, with a review of every decision at the end.

Follow production logs from applications through collection, parsing, filtering, buffering, sharded indexing, and search. Trigger traffic spikes, parser failures, and slow indexing to see where backpressure builds and logs can be lost.

Learn latency percentiles with an interactive simulator. Generate request samples, visualize distributions, compare average latency with P50, P90, P95, and P99, and see how tail latency affects real users.

Learn Business Continuity & Disaster Recovery with interactive RTO/RPO planning, failover strategies, and disaster scenarios. Understand hot, warm, and cold DR sites.

Learn Prometheus Query Language (PromQL) with an interactive playground. Master label filtering, rate calculations, aggregations, and histogram quantiles with real-time query execution.

Visualize OAuth 2.0 and OpenID Connect flows with an interactive simulator. Learn authorization code + PKCE, state, nonce, redirect URI checks, ID tokens, access tokens, refresh tokens, scopes, UserInfo, and common auth failure modes.

Visualize how SSL/TLS handshakes work with certificate verification, key exchange, and cipher negotiation. Compare TLS 1.2 and 1.3 protocols.

Educational simulator to understand how DDoS attacks work with stunning real-time visualizations, multiple attack vectors, and protection mechanisms.

Read a real SMTP bounce and decide what it is and what to do about it. Twelve genuine failures from Gmail, Outlook, Postfix and Proofpoint: hard bounces, soft bounces, content blocks, rate limits and spam complaints. Learn why the 4xx and 5xx class digit is a hint rather than the answer, which bounces to suppress permanently, which to retry, and what each mistake costs you in lost subscribers or lost sending reputation.

Visualize how SMTP email delivery works from app submission through EHLO, STARTTLS, AUTH, MAIL FROM, RCPT TO, DATA, SPF, DKIM, DMARC, recipient MX relay, temporary failures and retries, auth failures, and inbox placement. Sponsored by SMTPfast.

Learn how DNS works with an interactive step-by-step simulator. Visualize the DNS hierarchy, understand caching at different levels, and see the difference between recursive and iterative queries.

Learn how different load balancing algorithms distribute traffic across servers. Experiment with Round Robin, Least Connections, IP Hash, and more. See how load balancers handle failures and optimize performance.

Interactive visualization showing the differences between TCP's reliable connection-oriented protocol and UDP's fast connectionless approach. See the 3-way handshake, packet loss, and retransmissions in action.

Follow a single HTTP/HTTPS packet through the entire network stack with stunning animations. Learn DNS, TCP, TLS, CDN, load balancing, and more!

Practice MongoDB queries in an interactive browser terminal. Learn find and projections, query operators like $lt, $gt, and $in, sort, skip, limit, countDocuments, insert, update, delete, and the aggregation pipeline with $match, $group, and $sort, against a small e-commerce dataset that runs live in your browser.

Practice SQL in an interactive browser terminal. Learn SELECT, WHERE, ORDER BY, DISTINCT, aggregates, GROUP BY, HAVING, JOINs, subqueries, and window functions against a small e-commerce schema, with single-table queries evaluated live and verified Postgres output.

Practice the psql tool and Postgres engine in an interactive browser terminal. Explore with meta-commands, read real EXPLAIN plans, add an index to turn a sequential scan into a bitmap index scan, and use BEGIN and ROLLBACK to make changes safe, all against a small e-commerce database with verified PostgreSQL output.

Visualize the PostgreSQL wire protocol with an interactive simulator. Step through TLS negotiation, StartupMessage, SCRAM authentication, simple queries, extended queries, RowDescription, DataRow streams, ErrorResponse, COPY, and ReadyForQuery.

Explore database replication, sharding, and scaling with an interactive simulator. Compare sync vs async replication, shard key choices, hot spots, failover behavior, read replicas, write scaling, connection pooling, cost, and latency.

Learn how database indexes work with an interactive simulator. See the difference between full table scans and index seeks, understand B-tree structure, and learn when to create indexes.

Learn caching fundamentals with an interactive simulator. Visualize cache hits, misses, eviction policies (LRU, LFU, FIFO), and understand write strategies.

Learn about different database types (SQL, NoSQL, Graph, Time-Series) and their use cases. Explore CAP theorem trade-offs and make informed database choices.

Fix broken Terraform state without destroying production. Eight puzzles with real Terraform output: a rename that would replace a database, an import that forces replacement, a stale lock, drift, count index shifts and more. Choose between moved, import and removed blocks and the state commands.

Learn Terraform basics in an interactive browser lab. Read and edit the HCL config, run init, validate, plan, apply, and destroy, and watch state react to your edits. A free, hands-on way to learn infrastructure as code with no AWS account.

Learn AWS networking fundamentals with an interactive VPC simulator. Visualize how traffic flows through public and private subnets, understand NAT Gateways, Internet Gateways, and route tables.

Interactive game to learn scaling strategies for web applications. Experiment with horizontal and vertical scaling, see the effects on performance, cost, and reliability with realistic pricing simulation and budget constraints.

Send a webhook through a production-style delivery flow. Change endpoint responses, watch retries and backoff, inspect real HMAC-SHA256 signatures, and redeliver the same message to see receiver-side deduplication.

Watch a coding agent run an agentic loop, one step at a time. A planner, a builder, and a judge cycle through plan, build, verify, and repeat until the goal is met. Toggle the separate judge off to see why an agent grading its own work ships confident bugs. An animation-first, interactive explainer of loop engineering and how it maps to Claude Code.

Visualize JavaScript promises, async/await, microtasks, task queues, setTimeout ordering, rejection handling, and Promise.all with an interactive event-loop simulator inspired by classic JavaScript visual guides.

Visualize how message queues work across Kafka and RabbitMQ patterns. Explore producers, brokers, topics, partitions, exchanges, queues, consumer groups, lag, rebalancing, backpressure, ordering, and dead letter queues.

Compare REST and GraphQL side-by-side. Understand over-fetching, under-fetching, the N+1 problem, and when to use each approach with interactive scenarios.

Design and deploy microservices. See communication patterns, handle failures, and scale independently. Learn when to use microservices and understand the trade-offs.

Learn API rate limiting, backoff strategies, and throttling with real-time visualization and interactive charts.