Show HN: Paper trading that simulates real market dynamics and broker rules

  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?