New: labs that run the real program, in 3DRead it, run it,
Read it, run it,
remember it.
Run a cache, a loan, a price war. Then read why it broke.System design, AI, finance, game theory and more, from zero.
All in the browser, nothing to install: 617 lessons, 92 labs, 219 videos and 18 tracks.
watch one of 219 videoslesson one of every track is free, an account opens lessons 2 and 3, a plan the rest
the path
One track, start to finish.
Each module is a lesson, the board it is built on, and where one exists a video and a lab, with review cards at the end.
- 1The stall gets famous5 lessons · 5 boards · 5 videos · 7 labsstarts free
- 2When the stalls must agree5 lessons · 5 boards · 4 videos · 7 labsplan
- 3Holding up under load4 lessons · 1 board · 1 video · 1 labplan
- 4The parts, properly9 lessons · 4 boards · 3 videos · 2 labsplan
- 5Deeper than the interview6 lessonsplan
- 6The interview, assembled2 lessons · 2 boardsplan
- 1Neurons to a language model9 lessons · 5 boards · 4 videos · 2 labsstarts free
- 2From a model to an app7 lessons · 5 boards · 7 videos · 4 labsplan
- 3Past the basics12 lessons · 7 boards · 8 videos · 2 labsplan
- 4The string and the contract4 lessons · 4 boardsplan
- 5The loop and its harness8 lessons · 7 boards · 1 labplan
- 6GPT, built from scratch6 lessonsplan
- 1The toolbox7 lessons · 7 boards · 1 video · 2 labsstarts free
- 2Choosing the attack5 lessons · 4 boards · 1 labplan
- 3Worked, and deeper9 lessons · 6 boards · 2 labsplan
- 4DSA, in Hinglish10 lessons · 10 boards · 2 labsplan
- 5Clinic: arrays, hashing and stacks7 lessons · 7 boardsplan
- 6Clinic: search, trees, graphs and heaps9 lessons · 9 boardsplan
what you get
One idea, five ways in.
- boardsSketch-style drawings that hold a whole idea on one page.
- lessonsShort reads around each board, in order across 106 modules.
- videosNarrated explainers where the drawing moves as the voice explains.
- labsSimulations you run. Change one number, see what breaks.
- review cardsThe questions at the end of each lesson, brought back on a schedule.
try one
Every lab is a dial you can move.
Slate too smallOne line finds 34%, the rest walk to the ledger.3 lines: 9.0 ms. 6 lines: 6.0 ms.
start with the chai stall that got famous
0 of 73 read in System Design
how it works
Three steps, one idea a night.
Read the board
Every idea starts as one sketch with a short lesson around it. A story first, the jargon after.
open lesson one
Run the lab
Move one number, like cache size or queue load, and watch the idea hold or break in front of you.
browse 92 labs
Recall it cold
Each lesson ends with questions. Review brings them back days later, before you forget.
see the review deck
who it is for
For anyone tired of nodding along.
Interview prepA ten-week plan for the whole loop: DSA with 169 free LeetCode problems, system design, low-level design, and a timed mock round.Changing lanesA backend engineer moving into AI, or a frontend dev who wants to know what the database does with a write.Filling the gapsSelf-taught or bootcamp trained, and tired of nodding along when someone says consensus or TLB.Just curiousHow a packet crosses the internet, how a CPU runs a loop, how an LLM picks its next word.
questions the labs answer
Questions the labs answer
- System DesignMost orders are for three favourites. How big does the slate need to be before a bigger one stops helping?
- System DesignThe kitchen is 95% busy. How much longer do you wait than at 50%?
- System DesignThe limit is 5 a minute. How many can one client land in a two-second span?
- System DesignThe line between the branches is cut. What does the far clerk say to the customer in front of them?
- System DesignThe reply never arrived. Did the money move, and what should the client do?
- System DesignOne transfer, two books, and a crash that lands between them. Where does the money end up?
- Mind BlownThe test is 99% accurate and you tested positive. What are the odds you have it?
- System DesignEvery sale goes in the register and must also reach the warehouse. The app crashes now and then. Which design lets the two disagree?
- AIOne sentence, one tokenizer, a vocabulary you can grow. How many tokens does it cost?
- Game TheoryBetraying is the rational move in a single game. How many rounds before staying silent starts to win?
- NetworkingThe post loses one page in ten. What should you send again, and how much does the answer cost?
- DSAMerge sort is O(n log n) and insertion sort is O(n squared). On the list you actually have, which does less work?
- AIOne GPU, one chat, cores 99% idle. How many more chats fit before anything gets slower?
- AIThe filter has scored every email. How sure must it be before one goes to the spam folder?
- Data SystemsWrite-heavy wants an LSM, read-heavy wants a B-tree. Where exactly is the flip?
- DSAA million items. O(n log n) finishes in a blink. How long does O(n²) take?
- From ScratchYou start ten consumers against a four-partition topic. How many of them do any work?
- Database InternalsYour query has an index and Postgres refuses to use it. At what fraction of the table does reading all of it in order start to win?
- How Computers WorkThe device taps the CPU on every event. What happens when it taps a million times a second?
- How Computers WorkYou asked for four bytes. Sixty-four arrived. Who paid for the other sixty, and who else wanted them?
- DSAThe same recursion runs three ways. Which one solves ways(3) fifty-five times, and which solves it once?
- Database InternalsYou checkpoint three times as often for a faster restart. Why does the log get bigger?
- NetworkingYou changed the address. How long until the world stops sending people to the old one?
- Mind BlownThe new road is free, instant, and takes nothing away. Why is everybody's drive fifteen minutes longer?
- AIDoubling the experts doubles what the model knows and costs nothing per token. So what does it cost?
- System DesignEvery stall is slow one time in a hundred. An order that waits on a hundred stalls is slow how often?
- System DesignA hundred thousand different customers, and a tally board of 12 KB. How far off is its count?
- AIThe returns desk's loop keeps asking the model until it answers. How many passes before it hands the customer to a person?
- AIEvery step of training walks the dials downhill. How far should each step go?
- AIFine-tuning a 7B model with LoRA trains a small correction beside the frozen weights. How big should the correction be?
- DevOpsSpot is 63.6% cheaper than on-demand, and it can be taken back. How much of the fleet should run on it?
- DSAEvery find walks a chain of houses up to the root. In the worst order, how long can that chain get, and what keeps it short?
- Game TheoryThe incumbent swears it will start a price war if you enter. When should you believe it?
- Game TheoryBuyers can't tell a good used car from a lemon. How many lemons does it take before good cars stop selling?
- How Things WorkOne extension strip, one fuse, one cord. Plug in one more thing. Which fails first?
- How Things WorkA fridge and an air conditioner run the same loop. Why does one move twice as much heat per joule?
- Personal DevelopmentThe essay is due in 30 days and the phone pays now. On which day does the essay win?
- PsychologyA thousand labs test a pill that does nothing. How many publish that it works?
- Mind BlownA fund charges 1% a year. How much of your final balance does it take over thirty years?
- FinanceYou owe 5,000 at 24% a year. What does paying 100, 110 or 250 a month actually buy you?
- FinanceA right to buy one barrel of water at 100 in a year, when water costs 100 today. What is it worth, and what makes it worth more?
- FinanceThree banks send each other 48 payments in a day. Settle each the moment it is made, or pay only the difference at 17:00?
- SecurityYou sign a stolen login out everywhere. How long does the thief's copy keep working?
- SecurityAn attacker must get through every stage of a breach unseen. How good must each control be?
- How Computers WorkThe program needs twelve pages at once. What happens when it gets eleven frames?
- Database InternalsYour sort spills to disk. Give it more memory and it stops. Why does nobody set work_mem to a gigabyte?
- System DesignSixteen customers, one wala. If the wala stops standing at each kettle, how much sooner is everyone served?
- System DesignNames are mostly A–D. You split A–M / N–Z. What happens?
- System DesignYou pay your tab at stall A and walk to stall B. What do they say you owe?
- System DesignTwo cities changed the same order a moment apart. Which change survives, and what did it cost to be sure?
- System DesignThe room splits in two. Both halves think they are in charge. Who is allowed to write?
- System DesignFourteen real queries, six datastores. Which one answers yours without a second system?
- System DesignThe same answer is correct under one promise and a violation under another. Which promise did you make?
- How Computers WorkSame data, same O(n), four access patterns. Why is one of them 31 times slower?
- NetworkingMove the split one bit and the street halves. How many machines fit, and how do they share one public address?
- DSAA hash map answers in one step, on average. What is the worst case, and when does it start to matter?
- NetworkingThe pipe is 100 Mbps and the file is 1 MB. Why does the round-trip time decide how long it takes?
- System DesignThe ring rehomes only 1/N of the keys when a server dies. So why does everyone run two hundred virtual nodes per server?
- AIThe model has read 'The weather today is'. How often does it say something other than sunny?
- Game TheoryIt is worth 70 coins to you. What should you write on the slip?
- Data SystemsTwo doctors each check that someone else is on call, both go off call, and both commit. Which level notices?
- DSATen cities, and you can check every possible route. Eleven, and you cannot. So what do you ship for the eleventh?
- From ScratchYour teammate pulled your branch yesterday. You rebase it onto main today. How many of their commits are still on it?
- DevOpsEvery algorithm looks identical on the benchmark. Which one is still standing when two requests in a hundred cost sixty times the rest?
- DevOpsYour packet passed both gates on the way in. Does the answer get back out?
- How Computers WorkYour program stores 0.1. What is actually in those 64 bits?
- Database InternalsOne transaction has been open for an hour and nobody noticed. Why is the table three times the size of its data?
- How Computers WorkYour write returned and the power cut a moment later. Is the record on the disk?
- How Computers WorkNinety-five percent of the job splits across cores. How much faster can it possibly finish?
- DevOpsYour traffic goes up eightfold in three minutes and the HPA is working perfectly. Who still gets an error?
- Mind BlownTwenty-three people and 365 days. Why is a shared birthday a coin flip, and what does that cost you in bits?
- DevOpsA backup every night, and someone drops the main table at 11:59 pm. What is the cheapest way to lose under a minute of writes instead of a day?
- System DesignTen vadas left and a crowd reaching at once. How does the stall sell exactly ten, and what does making sure cost?
- AIThe returns desk cuts its policy into pieces and hands the model the best few. How big should a piece be, and how many should go in?
- AIEvery request goes to the small model first. How sure must it be before its answer goes out?
- DevOpsEach ship books quay space before it docks, and the harbour master trusts the booking. How much should a ship book?
- DSAGrabbing the biggest coin that fits gives the fewest coins with 1, 5, 10 and 25. Does it with any coins?
- Data SystemsA tap from a phone in a tunnel arrives twenty seconds late. How long should the server wait before showing a count?
- Game TheorySome birds always fight for food and some always back off. What share of fighters does a population settle at?
- Game TheoryTwo sellers share a market. Does competition between them push the price all the way down to cost?
- How Things WorkA child steps out where a 50 km/h car would just stop. How fast is a 60 km/h car still going there?
- How Things WorkIt is 40 °C. Does a fan help, and does the answer change when the air is wet?
- PhilosophyYou must pick a society's rules before you know which of its hundred people you will be. Which do you pick?
- Mind BlownYou picked a door and the host showed goats behind the others. Should you switch?
- Mind BlownOpen surgery wins on small stones and on large stones. How does it lose overall?
- FinanceEach river swings 20% a year and shares some weather. Own a hundred: how much does your water still swing?
- FinanceBorrow two buckets for every one you own and pour all three into a market averaging 7% a year. Do you end up with more water?
- FinanceCard payouts reach the bank days late, and two payments never arrive. How long should an entry wait for its twin before someone is told?
- SecurityA million password hashes have been stolen. How much does a slower hash actually buy you?
- NetworkingA bigger waiting yard means fewer parcels turned away. Why does it make the whole house feel slower?
- How Computers WorkThree long jobs are running when you press a key. How long until the keypress gets the CPU?
- Data SystemsA follower sends a heartbeat every second and the leader gives up after some silence. How much silence is enough?
pricing
Lesson one is free. A plan opens everything.
Launch price: 50% off your first payment with LAUNCH50, ends 1 Nov, 18:30 UTC.
Free
$0
The first lesson of every track, with its boards and videos, and the labs at the top of this page. A free account opens lessons 2 and 3 of every track.
Start readingYearly
$39$19.50/yearfirst year, then $39/year
Everything on chalk. Cancel anytime and keep access to the end of your paid year.
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Lifetime
$89$44.50 onceone-time payment
Pay once. Every lesson added later is included.
Get lifetimeTaxes, where applicable, are calculated at checkout. 14-day refunds on either plan.
questions
Before you start
Do I need a background in computer science?
No. Every track starts from the basics and builds up, and each idea is told as a story before it gets its proper name.
What is free?
The first lesson of every track, with its boards and videos, plus a few lessons, labs and papers picked for the home page. No account needed. A free account opens lessons 2 and 3 of every track, 33 more lessons.
What do I get with a plan?
All 617 lessons, every board, video, lab and paper, and the full review decks, synced across your devices.
Can I get a refund?
Yes, within 14 days, on either plan. Refund policy.
What if chalk ever shuts down?
You get at least 60 days of notice by email, and the unused part of what you paid comes back: the rest of a yearly plan, or for lifetime, the unused part of the 2 years after you bought it. Refund policy.
Is it written by AI?
AI tools helped build chalk. Everything is reviewed before it goes up, and the terms page says how. Terms.
Does it work on a phone?
Yes. Lessons, boards and videos are laid out for a phone, and the labs run in the browser with nothing to install.