Reading about an index is useful. Adding one and watching a query go from reading 20,000 rows to reading 10 is how it sticks. That is why we built the practice hub: a lab for each kind of work, where you run your own work in a real tool in the browser, instead of only answering questions about it.
Six labs are live now. This post lists what they do, what is free, and what Plus adds, without the marketing gloss. If something here doesn't match what you see in the labs, the labs are right, and please tell us.
The six live labs
- SQL Lab. Real PostgreSQL running in your browser, with retail, fintech and logistics sample databases. A schema explorer, a result grid, a query plan viewer, an index lab that times the same query with and without an index, CSV import, and a two-session locking demo.
- Code Lab. Run JavaScript, TypeScript and Python in a sandbox, write tests, and preview React components in a phone frame.
- System Design Studio. Build an architecture from servers, caches, queues and databases on a canvas, size each part, run traffic through it, and press Find my limit to see the users and requests a second it holds, and what it costs. Daily incident drills live here too.
- Security Lab. Patch a deliberately vulnerable Mangrove Market mini-app and prove the attack stops working: injection, output encoding, broken authentication, and access to other people's records. Plus log hunting and detection rules. It is for authorised learning only: everything runs locally against fake data, with no real targets and no outbound network.
- QA Lab. Read failing boundary tests, fix the code, and write your own acceptance criteria. Its campaign uses mutation testing: your tests are scored by how many hidden bugs they catch.
- DevOps & TechOps Lab. A browser terminal with a simulated Linux file system and git, a CI/CD pipeline builder you can run, and an incident console with metrics, logs and a runbook.
Every lab has two halves. The open lab is a workbench where you do whatever you like, starting from examples. The campaigns are graded challenge sets: solve them, climb the campaign board, and earn a badge that counts toward your Builder rank.
Your code runs in a sandbox in your browser. When you submit a campaign answer, the server checks it again in its own sandbox, so the boards stay fair.
What is free
The open labs are free with an account, and the first campaign in every lab is free.
| Lab | Free campaign | Free open lab includes |
|---|---|---|
| SQL Lab | SQL Basics (6 challenges) | All three sample databases, plan viewer, index lab, locking demo, examples, CSV import up to 1 MB |
| Code Lab | JS Basics (5) | JavaScript, TypeScript and Python, tests, React preview, examples |
| System Design Studio | Fundamentals (7 levels) | Up to 12 parts, load tests up to 10,000 req/s, one failure check, examples, PNG and JSON export |
| Security Lab | Patch the basics (4) | Two case studies, your own patches and criteria |
| QA Lab | Kill the mutants (6) | Two case studies, your own tests and criteria |
| DevOps & TechOps Lab | First commands (6) | Terminal, pipeline builder, incident console |
On the free plan you can save 5 projects in each lab. In the System Design Studio, the daily incident drill is free too: one drill a day, changing at midnight UTC, with its own streak.
And as before, everything outside the labs stays free for everyone: every course, lesson, podcast episode, exercise, quiz, final exam and certificate.
What Plus adds
Plus costs ৳350 for 30 days. You pay with bKash, and it does not renew automatically. Here is what it adds, lab by lab:
- Every other campaign. SQL: Fix the slow report and Data detective. Code: Async puzzles and Refactor kata. System Design Studio: URL shortener, Video platform, Payments at scale, and Route through the app. Security: Defender's desk and Harden the handler. DevOps: Fix the broken pipeline and Night shift on-call.
- The full incident drill library, any drill at any time, instead of today's drill only.
- In the System Design Studio: up to 30 parts, load tests above 10,000 req/s, zones and more failure checks, chaos mode, the scenario library and shape templates.
- In the SQL and Code Labs: the full example library, and CSV import up to 20 MB in the SQL Lab.
- In the Security and QA Labs: the full case-study library.
- Version history in the Studio and in the SQL, Code, Security and QA Labs: every save keeps the earlier version, so you can go back.
- More saved projects than the free plan's 5 per lab.
Plus also includes AI help in the labs where it is switched on: a hint, "explain my error", and a review of your design or criteria. It has a fair-use limit of 60 requests a month and 20 an hour. When the site's daily AI budget runs out, AI help pauses until the next day and your own allowance isn't used.
The pricing page has the current price and explains how paying with bKash works.
What is not here yet
Four more labs are listed on the hub as coming soon. Each has a page describing what it will do, but none is built yet:
- Data Lab: notebook cells with pandas and charts over the same sample databases as the SQL Lab.
- Finance Lab: a spreadsheet grid with models for unit economics, break-even, budgets and discounted cash flow.
- Product & BA Lab: PRD canvas, prioritisation boards, metric trees and process maps.
- AI Lab: a prompt playground with test sets, and building small apps from a description.
We will write here when each one opens.
Where to start
If you are not sure which lab is yours, start with the one closest to your role path, and do its free campaign first. It is short, it is graded, and it tells you quickly whether the lab suits how you learn.
Three walkthroughs to get you going:
- Read a query plan in 10 minutes, in the SQL Lab.
- Find your system's limit before your users do, in the System Design Studio.
- Switching from QA to developer, which uses the Code and QA Labs along the way.
The labs are new, so some rough edges are certain. When something confuses you, it is probably our fault, not yours: tell us, and we will fix it.