Hey HN! I built Paper, a paper trading platform that actually simulates the messy reality of trading - slippage, partial
fills, market impact, and real execution logic.
The Problem: Most paper trading platforms give you fantasy fills at perfect prices. You develop a strategy that works great
in simulation, then lose money when you go live because it never accounted for real market dynamics.
What Makes Paper Different:
- Simulates 22 real brokers with their exact rules, restrictions, and fee structures
- Real market dynamics: slippage, partial fills, market impact
- Configurable latency profiles: Retail (50-250ms), Institutional (20-100ms), Colocated (0.5-5ms), or Custom
- L1 NBBO price feeds with realistic fill prices
- Extended hours trading (4am-8pm ET)
- Full margin trading (Reg T and Portfolio Margin with SIMPLE/SPAN/TIMS)
- Short selling with proper locate requirements
- Real PDT rule enforcement
First Trading Platform with MCP (Model Context Protocol):
We're the first to ship MCP support! Test your trading strategies with Claude directly:
- npm install @paperinvest/mcp-server
- Build and backtest strategies using AI
- Claude can place trades, check positions, analyze performance
- Full API access through MCP tools
Tech Stack:
- NestJS backend with PostgreSQL, Redis, Kafka
- Next.js 15 frontend
- SSE for real-time order streaming
- REST API + MCP server
- AWS deployment
Pricing:
- Free: 5 trades/day, basic orders, cash account
- Pro ($20/mo): Unlimited trades, all order types, margin accounts, extended hours
- Commercial ($500+/mo): Multi-account support for businesses
Coming Soon: Options trading (full multi-leg strategies) and futures
I'm a solo developer. Built this because I was tired of strategies that worked perfectly in ThinkorSwim's paper trading but
failed with real money due to unrealistic fills.
Try it: https://paperinvest.io
API Docs: https://docs.paperinvest.io
Would love feedback! What broker rules or market dynamics do you wish paper trading platforms simulated better?