Polygon.io

Massive (formerly Polygon.io) is a real-time and historical market data API providing institutional-grade financial data across stocks, options, indices, forex, and crypto. Developers use it for building trading and fintech applications with WebSocket streaming, REST API, SQL query access, and flat file exports.

website | docs | npm: @polygon.io/client-js

Overview

Category	Finance
Compliance	SOC2, GDPR
Self-Hostable	No
On-Prem	No
Best For	startup, growth, enterprise
Last Verified	2026-02-13

Strengths & Weaknesses

Strengths:

performance
reliability
dx

Weaknesses:

expensive
overkill for simple needs
steep learning curve for SQL access

When to Use

Best when:

real-time trading apps
need WebSocket
production systems
SQL query access needed
large-scale data consumption
institutional-grade financial data

Avoid if:

budget constrained
only need basic data
no need for institutional-level data depth

Alternatives

finnhub, alpaca