What is market-feed?

market-feed is a TypeScript library that provides a unified interface to free financial market data APIs — plus a growing toolkit of analysis and UI utilities built on top of it.

The problem

Every free financial API speaks a different language:

// Yahoo Finance
const price = data.chart.result[0].meta.regularMarketPrice;

// Alpha Vantage
const price = parseFloat(data["Global Quote"]["05. price"]);

// Polygon.io
const price = data.ticker.lastTrade.p;

Beyond the data shape inconsistencies, you also have to deal with:

• No caching — every render or request re-fetches from the provider
• Rate limits — Alpha Vantage free tier is 25 calls/day; Polygon is 5 calls/minute
• No fallback — if Yahoo's unofficial API is temporarily down, your app breaks
• Boilerplate — retry logic, timeout handling, and error normalisation rewritten for every project

The solution

import { MarketFeed } from "market-feed";

const feed = new MarketFeed();

const quote = await feed.quote("AAPL");
console.log(quote.price); // always a number, always the same field name

One interface. Six providers. Cache, retry, fallback — all built in.

Design goals

Goal	How
Consistent types	Every provider returns the same Quote, HistoricalBar, CompanyProfile shape
Zero dependencies	Uses native fetch — runs in Node, Bun, Deno, CF Workers without polyfills
Strict TypeScript	No any. Full inference. Works with strict: true
Smart defaults	Works out-of-the-box with Yahoo Finance — no API key required
Transparent	raw: true exposes the original provider response when you need it
Modular	Sixteen optional subpath modules — import only what you use

Beyond the core client

market-feed ships a full analysis toolkit as opt-in subpath modules:

• Exchange Calendar — synchronous, offline-capable session and holiday detection for 8 exchanges + crypto
• HTTP Polling Stream — market-hours-aware async generator that pauses overnight and on weekends
• WebSocket Streaming — true tick-by-tick trade data from Polygon and Finnhub
• Price Consensus — query all providers in parallel, get a statistically weighted result
• Technical Indicators — SMA, EMA, RSI, MACD, Bollinger Bands, ATR, VWAP, Stochastic
• Portfolio — track positions and compute live P&L
• Backtesting — test entry/exit strategies against historical data
• Price Alerts — fire events when price, change%, or volume conditions are met
• Fundamentals — income statements, balance sheets, cash flow statements
• Stock Screener — filter a universe of symbols by any criteria
• Options Chain — full options chain with Greeks from Polygon.io
• Macro Indicators — 15 FRED economic series (CPI, GDP, Fed Funds…)
• React Hooks — useQuote, useStream, useAlerts, useWebSocket, useOrderBook for React ≥ 18 and React Native
• Browser Bundle — CORS proxy utilities for running market-feed client-side
• tRPC / HTTP Router — expose market data as typed tRPC procedures or a REST API
• Persistent Cache Drivers — Redis, Upstash, and SQLite drivers for market-feed/cache

What market-feed is NOT

• A paid data service — it wraps free APIs that have rate limits and data delays
• A trading platform — the data is for informational use only

Browser usage

Most financial APIs block CORS requests from browsers. Run market-feed server-side (API routes, server components, edge functions) and pass data to the client. If you need browser-side fetching, market-feed/browser provides CORS proxy utilities.