¶01 - free lld & system design interview prep
The complete Low-Level Design (LLD) interview preparation platform: a UML editor that understands OOP, 23 pre-wired design patterns, SOLID principles notes, timed practice with real analytics, 110+ curated LLD and system design interview questions with community discussion, and runnable code - all in one canvas, not seven different tools.
no account needed to try it
ParkingLot
- levels: List<Level>
+ getAvailableSpot(): Spot
«interface»
FeeStrategy
+ calculate(t: Ticket): float
Level
- spots: List<Spot>
+ getFreeSpot(): Spot
Vehicle
- licensePlate: String
- type: VehicleType
ParkingLot
- levels: List<Level>
+ getAvailableSpot(): Spot
110+
Practice problems
23
Design patterns
13
Class roles
7
Relationship types
11
Runnable languages
5
Export formats
¶02 - the complete lld & system design toolkit
Most candidates cobble together a UML diagramming tool, a system design questions site, a timer app, and a notes doc - solo. Here's the platform that replaces all of them for Low-Level Design and system design interview practice, teammates included - eight surfaces on one shelf. Pick one to open it.
01
5 node types, 7 relationship types, 3 canvas themes - keyboard-first, drag-to-connect.
Every relationship carries real UML semantics - a filled diamond always means composition, not just a line.
Undo/redo, alignment guides, and PNG, SVG, PlantUML, and Mermaid export, all reachable from the keyboard.
02
23 Gang-of-Four patterns and 13 class-role stereotypes, pre-wired and correctly connected.
Every pattern ships with the correct handle sides pre-computed - no arrows crossing through boxes.
Insert any of the 23 with a single Ctrl+K search instead of digging through a sidebar.
03
Plain-English sentences in, a live UML diagram out - instantly, as you type.
Round-trips both ways - export any diagram back to Draft Notation text and re-import it later.
The same parser powers the standalone Playground and the one-shot importer inside the editor.
04
Timed LLD interview practice against a real countdown. Every session becomes a streak, a heatmap, a graph.
Pick 30, 45, 60, 90 minutes, or go unlimited - pause and resume without losing the clock.
Every session auto-saves a snapshot, so an unfinished attempt is never actually lost.
05
110+ LLD & system design interview questions, curated by company and difficulty, with staged hints and real discussion threads.
Three hints unlock one at a time, so you're never spoiled all at once.
See how other engineers structured the same design before you settle on your own.
06
Bite-sized theory - bookmarked, tracked, ready for a five-minute refresher.
Each note tracks its own bookmarked and revised state per user, so your list stays accurate.
Organized by category and difficulty - basic, intermediate, advanced - so revision is never random.
07
Turn the class you just drew into real, runnable code - 11 languages, no separate IDE.
The exact same sandbox that powers the standalone Playground's Run button.
Rate-limited and abuse-protected server-side, so it stays fast and free for everyone.
08
Invite teammates into the same diagram in real time, and leave threaded comments right on the canvas.
See collaborators' cursors and edits live - no refresh, no manual merging.
Comments stay pinned to the exact node they're about, tagged with @mentions, not lost in a separate doc.
5 node types, 7 relationship types, 3 canvas themes - keyboard-first, drag-to-connect.
Every relationship carries real UML semantics - a filled diamond always means composition, not just a line.
Undo/redo, alignment guides, and PNG, SVG, PlantUML, and Mermaid export, all reachable from the keyboard.
23 Gang-of-Four patterns and 13 class-role stereotypes, pre-wired and correctly connected.
Every pattern ships with the correct handle sides pre-computed - no arrows crossing through boxes.
Insert any of the 23 with a single Ctrl+K search instead of digging through a sidebar.
Plain-English sentences in, a live UML diagram out - instantly, as you type.
Round-trips both ways - export any diagram back to Draft Notation text and re-import it later.
The same parser powers the standalone Playground and the one-shot importer inside the editor.
Timed LLD interview practice against a real countdown. Every session becomes a streak, a heatmap, a graph.
Pick 30, 45, 60, 90 minutes, or go unlimited - pause and resume without losing the clock.
Every session auto-saves a snapshot, so an unfinished attempt is never actually lost.
110+ LLD & system design interview questions, curated by company and difficulty, with staged hints and real discussion threads.
Three hints unlock one at a time, so you're never spoiled all at once.
See how other engineers structured the same design before you settle on your own.
Bite-sized theory - bookmarked, tracked, ready for a five-minute refresher.
Each note tracks its own bookmarked and revised state per user, so your list stays accurate.
Organized by category and difficulty - basic, intermediate, advanced - so revision is never random.
Turn the class you just drew into real, runnable code - 11 languages, no separate IDE.
The exact same sandbox that powers the standalone Playground's Run button.
Rate-limited and abuse-protected server-side, so it stays fast and free for everyone.
Invite teammates into the same diagram in real time, and leave threaded comments right on the canvas.
See collaborators' cursors and edits live - no refresh, no manual merging.
Comments stay pinned to the exact node they're about, tagged with @mentions, not lost in a separate doc.
¶03 - the uml class diagram editor
A UML diagram editor built for Low-Level Design interviews specifically - instant class insertion, drag-to-connect relationships, a searchable design-pattern library, and export to the formats your design docs actually use.
¶04 - draft notation - code ↔ diagram
No angle brackets, no drag-and-drop required. Describe a Low-Level Design in a sentence like User has many Post and the relationship, the arrow, and the multiplicity all render themselves - instantly, live, as you type.
Round-trips both ways - export any diagram back to Draft Notation text whenever you need words instead of boxes.
The exact same parser powers the standalone Playground and the one-shot Draft importer inside the editor.
Describe a design out loud in an interview the way you'd actually say it, then watch it become the artifact you submit.
▍User
+ id:
+ name: String
+ email: String
+ login()
+ getProfile(): Profile
Post
+ id:
+ content: String
¶05 - lldcanvas vs. generic diagramming tools
Generic tools draw shapes. LLDCanvas is purpose-built for Low-Level Design and system design interview preparation - here's exactly what that gets you.
¶06 - timed lld interview practice
Set a timer and design against a real countdown - the exact pressure you'll feel in an actual LLD or system design interview, so the first time you work under a clock isn't the day it counts. Every session is then logged automatically: watch a daily streak build, an activity heatmap fill in week by week, and a practice-time graph trend upward.
Most candidates only ever practice untimed - the clock is the one part nobody rehearses.
A visible streak turns "I should probably practice" into something you actually do, daily.
Every canvas and note is saved automatically the moment you stop - nothing to set up first.
Your practice activity
Design a Parking Lot
sped up - real sessions run the full 45
Last 14 weeks
Minutes per week
42
Sessions logged
18h 20m
Time practiced
12 days
Current streak
¶07 - lld & system design interview questions
110+ Low-Level Design and system design interview questions and problems, each tagged by difficulty and the companies known to ask it. Staged hints reveal one at a time - never all at once. Compare your approach against the community thread when you're done.
Problem Library
110+ problemsCurrently solving
Design a Parking Lot
Model the lot, levels, spots, and a fee strategy that varies by vehicle type and duration.
By difficulty
Asked by
Staged Hints
Hint 2 of 3 ↓
Think about counting requests over a sliding window - not fixed intervals.
Community Discussion
127 postsUsed token bucket over leaky bucket - way simpler to handle burst allowance. Shared my full canvas diagram in the thread ↗
@Priya How did you handle distributed counting across nodes? Redis sorted sets?
¶08 - solid principles & system design fundamentals
Bite-sized theory on SOLID principles, composition vs. inheritance, thread-safety, the CAP theorem, and more - bookmark what to revisit, and track what's actually sunk in.
hover to revise →
Basic
Five rules for classes that survive contact with new requirements - start with Single Responsibility, the other four follow from it.
SOLID Principles
hover to revise →
Basic
Favor "has-a" over "is-a" when behavior needs to change at runtime - inheritance locks in a shape at compile time.
Composition vs. Inheritance
hover to revise →
Intermediate
Double-checked locking exists because synchronizing the whole getInstance() call is correct but needlessly slow after the first call.
Singleton Thread-Safety
hover to revise →
Intermediate
REST models resources and state transitions; RPC models actions. Pick RPC when the operation isn't naturally a noun.
REST vs. RPC
hover to revise →
Advanced
Under a network partition you choose Consistency or Availability - you never get to skip that choice, only which side you land on.
CAP Theorem
hover to revise →
Advanced
An idempotency key lets a client safely retry a POST after a timeout without risking a duplicate charge or write.
Idempotency in APIs
¶09 - from diagram to running code
Sketch the class in the canvas, then execute it in 11 languages without leaving the tab. No copy-paste into a separate IDE - design and code live side by side.
Design
- rate : float
- maxHours : int
+ calculate(t)
+ getRate()
1class FeeStrategy:2 def calculate(self, ticket):3 hours = ticket.duration_hours()4 return max(hours, 1) * 2.556 def get_rate(self) -> float:7 return self._rate
¶10 - work with others
Invite a teammate into your diagram and work side by side - live cursors, pinned comments, and real-time edits, no refresh needed.
Live cursors & presence - See every teammate's cursor in real time - no refresh, no manual sync.
Pinned @mention comments - Threads stay anchored to the exact node they're about, not buried in chat.
Invite by email or link - Collaborators get viewer or editor roles the moment they accept.
Real stories from developers who aced their LLD and system design interview rounds.
“LLDCanvas completely changed how I prepare for system design interviews. The visual diagram editor paired with the problem library is exactly what I needed.”
Arjun Mehta
SDE-2 @ Google
“I cracked my Amazon interview after using this platform for just 3 weeks. The Interview Mode timer made me so much faster at thinking through designs.”
Priya Sharma
CS Final Year, IIT Delhi
“The design pattern templates are a game changer. I can visualise any pattern in seconds and understand how it maps to real code.”
Rahul Gupta
Backend Engineer @ Swiggy
“Draft Notation is pure genius. Writing diagrams in plain English felt so natural. I recommended LLDCanvas to my entire team.”
Sneha Patel
SDE @ Microsoft
“Real-time collaboration means I can review LLD designs with my team synchronously. This is enterprise-grade tooling for free.”
Vikram Singh
Software Architect
“LLDCanvas completely changed how I prepare for system design interviews. The visual diagram editor paired with the problem library is exactly what I needed.”
Arjun Mehta
SDE-2 @ Google
“I cracked my Amazon interview after using this platform for just 3 weeks. The Interview Mode timer made me so much faster at thinking through designs.”
Priya Sharma
CS Final Year, IIT Delhi
“The design pattern templates are a game changer. I can visualise any pattern in seconds and understand how it maps to real code.”
Rahul Gupta
Backend Engineer @ Swiggy
“Draft Notation is pure genius. Writing diagrams in plain English felt so natural. I recommended LLDCanvas to my entire team.”
Sneha Patel
SDE @ Microsoft
“Real-time collaboration means I can review LLD designs with my team synchronously. This is enterprise-grade tooling for free.”
Vikram Singh
Software Architect
“The analytics showing my average time per problem helped me identify my weak spots. My design speed improved 40% in a month.”
Ananya Reddy
SDE-3 @ Flipkart
“As a student, having a free tier with 23 design patterns and community discussions is incredibly generous. I use this daily.”
Karan Bhatia
CS Student, NIT Trichy
“The community discussion on each problem is like having LeetCode discussions but specifically for LLD. Absolutely brilliant.”
Divya Nair
Product Engineer @ Razorpay
“Code execution integrated right into the diagram tool is something I have wanted for years. Finally it exists.”
Rohan Verma
Principal SDE @ Oracle
“My whole interview prep is now centralised - UML diagrams, pattern templates, code, problems - one platform, zero distractions.”
Meera Krishnan
Tech Lead @ PhonePe
“The analytics showing my average time per problem helped me identify my weak spots. My design speed improved 40% in a month.”
Ananya Reddy
SDE-3 @ Flipkart
“As a student, having a free tier with 23 design patterns and community discussions is incredibly generous. I use this daily.”
Karan Bhatia
CS Student, NIT Trichy
“The community discussion on each problem is like having LeetCode discussions but specifically for LLD. Absolutely brilliant.”
Divya Nair
Product Engineer @ Razorpay
“Code execution integrated right into the diagram tool is something I have wanted for years. Finally it exists.”
Rohan Verma
Principal SDE @ Oracle
“My whole interview prep is now centralised - UML diagrams, pattern templates, code, problems - one platform, zero distractions.”
Meera Krishnan
Tech Lead @ PhonePe
¶11 - lld & system design interview faqs
Common questions about Low-Level Design, system design interviews, and how LLDCanvas's free interview-prep platform works.
LLDCanvas is a free, all-in-one Low-Level Design (LLD) interview preparation platform: a UML class diagram editor, 23 pre-wired Gang-of-Four design patterns, a curated library of LLD and system design interview questions with staged hints and community discussion, timed Interview Mode with streaks and analytics, bite-sized revision notes on SOLID principles and OOP fundamentals, a plain-English code↔diagram language (Draft Notation), and a multi-language code execution sandbox - everything you need for LLD interview practice in one place, not scattered across seven different tools.
Low-Level Design (LLD) is the interview round where you design the classes, interfaces, and relationships that implement a system - think "design a Parking Lot" or "design a Rate Limiter" as actual code-level object-oriented design, not just architecture boxes. Interviewers evaluate your class diagrams, your use of design patterns and SOLID principles, and how cleanly your object model extends to new requirements. It sits between coding rounds (data structures & algorithms) and high-level System Design (load balancers, databases, scaling) - LLDCanvas is built specifically for practicing this round.
System Design (or High-Level Design) interviews focus on distributed-systems concerns - load balancing, database sharding, caching, and capacity estimation. LLD interviews focus one level down, on the actual object-oriented design: classes, interfaces, inheritance vs. composition, and design patterns for a single service or component. Many SDE interview loops include both. LLDCanvas is purpose-built for the LLD/OOD side - the UML editor, design patterns, and problems library - while also covering system-design-adjacent fundamentals like the CAP theorem, idempotency, and REST vs. RPC in the revision notes library.
draw.io and Lucidchart work with generic shapes. LLDCanvas works with classes. Every node is a real UML class node - with a header, attributes section, and methods section. Relationships carry real semantic meaning (a filled diamond is composition, a hollow triangle is inheritance) instead of being hand-drawn lines. You also get all 23 classic design pattern skeletons pre-wired, plus a full LLD interview-question library, timed interview drills, revision notes, and runnable code - none of which exist in generic diagramming tools.
A plain-English way to write class diagrams for LLD interview practice - describe classes and relationships in sentences like "User has many Post", and the UML diagram renders itself live as you type. Try it in the standalone Playground, or read the full syntax guide in the Docs.
A timed practice mode built to simulate the pressure of a real interview: set a duration, design against a real countdown, and every session is logged automatically into a daily streak, an activity heatmap, and progress analytics - so the first time you design under real interview pressure isn’t the day it counts.
Yes - a curated library of 110+ Low-Level Design problems and interview questions, tagged by difficulty (Easy, Medium, Hard) and by the companies known to ask them (Amazon, Google, Meta, Uber, Stripe, and more). Each problem ships with staged hints that unlock one at a time, plus a community discussion thread where you can compare your class diagram against other engineers’ submitted solutions.
All 23 classic Gang-of-Four design patterns - Singleton, Factory Method, Observer, Strategy, Decorator, Adapter, and 17 more - plus 13 class-role stereotypes for common object-oriented design (OOD) roles. Every pattern is pre-wired with the correct UML relationships and handle positions, so you can insert a working skeleton with Ctrl+K instead of drawing one from memory.
Yes - SOLID principles, composition vs. inheritance, thread-safety, the CAP theorem, idempotency, and REST vs. RPC are all covered as bite-sized revision notes, organized by difficulty (Basic, Intermediate, Advanced) so you can revise the fundamentals in minutes instead of re-reading a textbook chapter.
Yes - the editor and Playground both include a code execution panel supporting 11 languages (Python, Java, C++, Go, Rust, TypeScript, C#, Ruby, PHP, Haskell, F#), so you can turn a class you designed into real, runnable logic without leaving the canvas.
Yes - invite teammates into the same diagram and see their cursors and edits live, no refresh or manual merging required. You can also leave threaded comments pinned to a specific node, with @mentions to bring someone into the conversation - useful for mock interviews and pair design sessions, not just solo LLD practice.
No - open the local editor and start drawing immediately. No login, no install. Sign in only when you want cloud sync, Interview Mode history, the problems library, or revision notes tracking.
It migrates automatically - your local diagram is copied to your cloud account the moment you sign in, and you are redirected to it.
Yes. Export as PNG (for resumes, slide decks), SVG (scalable, for design docs), PlantUML text, Mermaid text (for GitHub READMEs, Notion, Confluence), or Draft Notation (plain-text, re-importable). All exports are available from the toolbar or the Ctrl+K command palette.
It’s free end to end and functions as a self-paced LLD and system design interview-prep curriculum, not just a drawing tool: the UML editor, all 23 design pattern skeletons, Draft Notation, Interview Mode, the full problems library, revision notes, and code execution are all free right now. Signing in (free, via Google or email) only adds cloud sync and progress tracking across devices - there’s no paywalled "premium course" version of the core learning content.
No - LLDCanvas is built to teach Low-Level Design from the fundamentals up. Start with the Basic-tier revision notes (SOLID principles, composition vs. inheritance), work through Easy problems in the library, and use Draft Notation to describe a design in plain English before you ever need to know UML syntax by heart.
Problems are tagged by the companies known to ask them in real interview loops, including Amazon, Google, Meta, Uber, and Stripe, alongside classics like Parking Lot, Rate Limiter, Elevator System, and Notification Service - so you can filter practice toward the companies you’re actually interviewing with.
It’s purpose-built for the LLD, object-oriented design, and design-patterns portion of software engineering interviews specifically - the round that pure DSA/LeetCode practice doesn’t cover. Most SDE interview loops (Amazon, Google, Meta, and similar) include an LLD or system-design round alongside coding rounds, so LLDCanvas is meant to sit alongside your algorithms prep, not replace it.
YourNextInterview
Create your first diagram in under 30 seconds.