Loading low-level design…

Design Zerodha - Low-Level Design | OneNoughtOne

00:00:00

Design Zerodha

Advanced

Design an object-oriented stock trading platform (like Zerodha) with trading accounts, stock listings with OHLCV data, multiple order types (Market, Limit, Stop-Loss, Stop-Limit), a price-time priority order book (matching engine), trade execution with fund settlement, and portfolio management with weighted-average cost P&L.

The platform supports margin management: BUY orders block funds upfront, SELL orders validate sufficient holdings. The order book matches the highest bid against the lowest ask using price-time priority (FIFO within the same price level). Partial fills keep orders open for the remaining quantity. Each trade computes brokerage (₹20 flat or 0.03%), STT, exchange fees, GST, and stamp duty.

Core Use Cases

Account management

Create trading + demat account; deposit and withdraw funds

Stock listing

List stocks with symbol, name, exchange, OHLCV (Open/High/Low/Close/Volume)

Place order

Place Market, Limit, Stop-Loss, or Stop-Limit orders for BUY or SELL

Margin management

Block balance as margin for BUY orders; validate holdings for SELL orders

Order matching

Price-time priority order book: highest bid meets lowest ask, FIFO within same price

Trade execution

Record trades, update holdings (add/remove), settle funds, update LTP

Portfolio & P&L

Holdings with weighted-average buy price, current value, P&L, P&L%

Cancel/modify order

Cancel open orders (release margin); modify via cancel-and-replace

Brokerage calculation

Brokerage (₹20 or 0.03%), STT, exchange fees, GST, stamp duty per trade

Constraints

BUY orders require sufficient balance (margin blocked upfront)
SELL orders require sufficient holdings in demat
Order book uses price-time priority: best price first, FIFO at same price
Execution price is the earlier (passive) order's price
Partial fills are supported — order remains OPEN for remaining quantity
Holdings use weighted-average cost (not FIFO/LIFO)

Assumptions

In-memory storage (no database or persistence)
Single-threaded (concurrency is a follow-up)
Equity delivery (CNC) only — F&O is a follow-up
Single exchange (NSE) — multi-exchange is a follow-up
No short selling (must own shares to sell)
Market orders execute at the best available price in the order book

In Scope

Trading account with balance and margin management
Stock with OHLCV data and price change tracking
Order types: Market, Limit, Stop-Loss, Stop-Limit
Order lifecycle: PENDING → OPEN → PARTIALLY_FILLED → FILLED
Order book with price-time priority matching
Trade execution with fund settlement and holding updates
Portfolio: holdings with weighted-average cost and P&L
Brokerage and statutory charges calculation
Order cancellation with margin release
Watchlist management

Out of Scope

F&O (Futures & Options) trading
Short selling and margin trading (MIS)
Multi-exchange routing
Real-time market data streaming
IPO and mutual fund modules
Tax reporting (P&L statements, capital gains)
Two-factor authentication

Approach Guide(Click to expand each section)

Before diving into code, clarify the use cases and edge cases. Understanding the problem deeply leads to better class design.

List Core Use Cases

Identify the primary actions users will perform. For a parking lot: park vehicle, exit vehicle, check availability. Each becomes a method.

Identify Actors

Who interacts with the system? Customers, admins, automated systems? Each actor type may need different interfaces.

Clarify Constraints

What are the limits? Max vehicles, supported vehicle types, payment methods. Constraints drive your data structures.

Ask About Edge Cases

What happens on overflow? Concurrent access? Payment failures? Thinking about edge cases reveals hidden complexity.

Follow-up Questions(Questions an interviewer might ask)

💡 Draw UML class diagrams, sequence diagrams, or any design visualizations. Submit from the Code tab.

Loading canvas...

Loading LLD design...

00:00:00

Design Zerodha

Advanced

Core Use Cases

Account management

Create trading + demat account; deposit and withdraw funds

Stock listing

List stocks with symbol, name, exchange, OHLCV (Open/High/Low/Close/Volume)

Place order

Place Market, Limit, Stop-Loss, or Stop-Limit orders for BUY or SELL

Margin management

Block balance as margin for BUY orders; validate holdings for SELL orders

Order matching

Price-time priority order book: highest bid meets lowest ask, FIFO within same price

Trade execution

Record trades, update holdings (add/remove), settle funds, update LTP

Portfolio & P&L

Holdings with weighted-average buy price, current value, P&L, P&L%

Cancel/modify order

Cancel open orders (release margin); modify via cancel-and-replace

Brokerage calculation

Brokerage (₹20 or 0.03%), STT, exchange fees, GST, stamp duty per trade

Constraints

BUY orders require sufficient balance (margin blocked upfront)
SELL orders require sufficient holdings in demat
Order book uses price-time priority: best price first, FIFO at same price
Execution price is the earlier (passive) order's price
Partial fills are supported — order remains OPEN for remaining quantity
Holdings use weighted-average cost (not FIFO/LIFO)

Assumptions

In-memory storage (no database or persistence)
Single-threaded (concurrency is a follow-up)
Equity delivery (CNC) only — F&O is a follow-up
Single exchange (NSE) — multi-exchange is a follow-up
No short selling (must own shares to sell)
Market orders execute at the best available price in the order book

In Scope

Trading account with balance and margin management
Stock with OHLCV data and price change tracking
Order types: Market, Limit, Stop-Loss, Stop-Limit
Order lifecycle: PENDING → OPEN → PARTIALLY_FILLED → FILLED
Order book with price-time priority matching
Trade execution with fund settlement and holding updates
Portfolio: holdings with weighted-average cost and P&L
Brokerage and statutory charges calculation
Order cancellation with margin release
Watchlist management

Out of Scope

F&O (Futures & Options) trading
Short selling and margin trading (MIS)
Multi-exchange routing
Real-time market data streaming
IPO and mutual fund modules
Tax reporting (P&L statements, capital gains)
Two-factor authentication

Approach Guide(Click to expand each section)

Before diving into code, clarify the use cases and edge cases. Understanding the problem deeply leads to better class design.

List Core Use Cases

Identify the primary actions users will perform. For a parking lot: park vehicle, exit vehicle, check availability. Each becomes a method.

Identify Actors

Who interacts with the system? Customers, admins, automated systems? Each actor type may need different interfaces.

Clarify Constraints

What are the limits? Max vehicles, supported vehicle types, payment methods. Constraints drive your data structures.

Ask About Edge Cases

What happens on overflow? Concurrent access? Payment failures? Thinking about edge cases reveals hidden complexity.

Follow-up Questions(Questions an interviewer might ask)

💡 Draw UML class diagrams, sequence diagrams, or any design visualizations. Submit from the Code tab.

Loading canvas...

Design Zerodha

Core Use Cases

Constraints

Assumptions

In Scope

Out of Scope

Approach Guide(Click to expand each section)

Follow-up Questions(Questions an interviewer might ask)

Explore the full editorial.

Sign in to view submissions

Design Zerodha

Core Use Cases

Constraints

Assumptions

In Scope

Out of Scope

Approach Guide(Click to expand each section)

Follow-up Questions(Questions an interviewer might ask)

Explore the full editorial.

Sign in to view submissions

Design Zerodha

Core Use Cases

Constraints

Assumptions

In Scope

Out of Scope

Approach Guide(Click to expand each section)

Gather Requirements~3 min

Identify Classes & Entities~4 min

Define Relationships~3 min

Apply Design Patterns~4 min

Apply SOLID Principles~3 min

Code Organization~2 min

Follow-up Questions(Questions an interviewer might ask)

1How would you handle concurrent order placement and matching?

2How would you add support for F&O (Futures & Options)?

3How would you implement a circuit breaker (price band limit)?

4How would you implement intraday (MIS) positions with auto-square-off?

5How would you optimize the order book for ultra-low latency?

Key Topics

Asked At

Explore the full editorial.

Sign in to view submissions

Design Zerodha

Core Use Cases

Constraints

Assumptions

In Scope

Out of Scope

Approach Guide(Click to expand each section)

Gather Requirements~3 min

Identify Classes & Entities~4 min

Define Relationships~3 min

Apply Design Patterns~4 min

Apply SOLID Principles~3 min

Code Organization~2 min

Follow-up Questions(Questions an interviewer might ask)

1How would you handle concurrent order placement and matching?

2How would you add support for F&O (Futures & Options)?

3How would you implement a circuit breaker (price band limit)?

4How would you implement intraday (MIS) positions with auto-square-off?

5How would you optimize the order book for ultra-low latency?

Key Topics

Asked At

Explore the full editorial.

Sign in to view submissions