Best System Design Interview Practice Platforms in 2026

Most system design prep is reading. You read a chapter on consistent hashing, you watch a video about designing YouTube, you nod along, and three weeks later you sit in front of an interviewer and discover that you cannot produce any of it on your own.

That gap is the whole problem. A system design interview is a performance: 45 minutes of turning a vague prompt into requirements, numbers, a diagram, and a defended set of tradeoffs, out loud, under time pressure. Reading builds vocabulary. Only practice builds the performance.

So this comparison sorts platforms by one question: what does each one make you do? Some teach, some make you produce a design and grade it, and some put a human across the table from you. You probably want one of each, not three of the same kind.

The short version

The rest of the article explains each choice.

What to look for in a practice platform

Before the list, four things that separate practice from reading:

1. You produce the design. If the platform shows you the answer before you have committed to your own, it is a course with extra steps. The value is in the struggle of making decisions with nothing to copy from.
2. The feedback is specific. "Good job, consider scalability" is useless. Useful feedback names the thing you missed: you never estimated write throughput, you put a cache in front of a write-heavy path, you did not say what happens when the queue backs up.
3. There is enough breadth. Interviewers rotate questions. You want dozens of problems across categories (feeds, storage, real-time, payments, search, infrastructure), not the same five classics.
4. It matches your target round. A senior backend loop, a machine learning system design round, an object-oriented design round and an agentic AI round are different interviews. Make sure the platform covers the one you are actually facing.

The platforms

Codemia

What it makes you do: produce a full design for a problem, then get graded.

Codemia was built on the idea in the title of this article: practise system design the way you practise algorithms on LeetCode. You pick a problem, write requirements, estimates and a high level design in the editor, draw the architecture on an interactive whiteboard, and submit. An AI evaluator grades the submission against a rubric for that specific problem and tells you which points you covered and which you missed, section by section. You can revise and resubmit, then compare your answer with an editorial solution and with other users' submissions.

• Breadth: 120+ system design problems, 70+ object-oriented design problems, 22 ML system design problems and 18 agentic AI design problems, plus 300+ DSA problems with visualisations.
• Human practice: free peer mock interviews with a shared whiteboard and video.
• Pricing model: a set of problems is free to practise; a paid plan unlocks the rest of the problems and the full editorials.
• Best for: the middle of your prep, when you know the vocabulary and need reps. Also the strongest option here if your loop includes an ML system design or agentic AI round.
• Weak spots: less video content than the course platforms, and no paid one-to-one coaching with professional interviewers.

Hello Interview

What it makes you do: work through a problem step by step with an AI tutor.

Hello Interview is known for its free written breakdowns of common questions, which are some of the best free reading on the web. Its paid guided practice walks you through a problem in stages (requirements, entities, API, high level design, deep dives) on a whiteboard, with AI feedback at each stage.

• Best for: candidates who want a structured script to follow, and anyone who likes learning from long, well written breakdowns.
• Weak spots: the guided format holds your hand, which helps early but is less like a real interview, where nobody tells you which stage comes next. The free tier of guided practice is a single problem.

Exponent (rebranding as Aced)

What it makes you do: watch, then rehearse with peers or an AI interviewer.

Exponent is a broad interview prep platform covering software engineering, product management, data science and more. For system design it offers a video course, a large library of recorded mock interview answers, free peer mock interviews (Exponent took over Pramp's peer matching), AI interviewer feedback on paid plans, and paid sessions with expert coaches.

• Best for: people preparing for several interview types at once, and anyone who learns well by watching other people do mock interviews.
• Weak spots: system design is one section among many, so the problem depth is thinner than on a dedicated platform.

ByteByteGo

What it makes you do: read.

ByteByteGo is Alex Xu's platform, built on the System Design Interview books. The diagrams are excellent and the explanations are clear. It now also covers coding patterns, object-oriented design and machine learning system design.

• Best for: the start of your prep, when you need to learn what a message queue, a CDN or a consistent hash ring is actually for.
• Weak spots: there is no practice loop. Reading a worked answer to "design a chat system" is not the same skill as producing one.

Design Gurus (Grokking the System Design Interview)

What it makes you do: read, with some interactive quizzes.

The Grokking course is the one that popularised the "here are the common problems and their patterns" approach. It is a structured text course, and the company has expanded into many related courses.

• Best for: a structured syllabus if you like courses with a clear order.
• Weak spots: same as ByteByteGo. It teaches answers rather than training you to produce them.

interviewing.io

What it makes you do: do a real mock interview with an engineer from a large tech company.

You book an anonymous mock interview with an experienced interviewer, do the interview, and get detailed written and verbal feedback. Its free Senior Engineer's Guide to the System Design Interview is also worth reading regardless of which platform you use.

• Best for: the last two to three weeks before a real loop, once your designs are solid and you need to rehearse under real pressure.
• Weak spots: cost. Paid mocks are expensive per session, so it makes sense for a few high value rehearsals, not for daily reps.

Free options

You can get a long way without paying anyone:

• A friend and a whiteboard tool. Excalidraw or tldraw plus a 45 minute timer. Take turns interviewing each other from a list of problems.
• Peer mock platforms. Exponent and Codemia both match you with other candidates for free.
• Free problem sets. Codemia's free problems and Hello Interview's free breakdowns.
• Engineering blogs. Netflix, Uber, Discord, Meta and Cloudflare all publish write-ups of real systems. Reading how a real team solved the problem is the best way to sharpen deep dives.

How to combine them

A plan that works for most people with four to eight weeks:

1. Weeks 1 to 2: learn. Pick one reading source (a book, ByteByteGo or Grokking) and cover the building blocks: load balancing, caching, databases and replication, sharding, queues, consistency models.
2. Weeks 2 to 6: practise. Do two or three full designs a week on a practice platform. Write the design yourself before reading any solution. After grading, write down the two points you missed and look for them on the next problem.
3. Weeks 4 to 7: rehearse. Add one peer mock a week. Speaking a design is a different skill from writing one.
4. Final 2 weeks: pressure test. One or two mocks with experienced interviewers if your budget allows.

The single most common mistake is staying in step 1 for too long. Reading feels productive and is comfortable. Producing a design and having it graded is uncomfortable, which is exactly why it works.

Start practising

If you want to start now, Codemia's system design problems begin with easy classics like a URL shortener and a parking lot and go up to hard problems like Ticketmaster and a metrics monitoring and alerting system. Pick one, set a 45 minute timer, and write your answer before you read anyone else's.