Massive (formerly Polygon.io) Go Client - WebSocket & RESTful APIs

The official Go client library for the Massive REST and WebSocket API. This client makes use of Go generics and thus requires Go 1.18. See the docs for more details on our API.

Note: Polygon.io has rebranded as Massive.com on Oct 30, 2025. Existing API keys, accounts, and integrations continue to work exactly as before. The only change in this SDK is that it now defaults to the new API base at api.massive.com, while api.polygon.io remains supported for an extended period.

For details, see our rebrand announcement blog post or open an issue / contact support@massive.com if you have questions.

Getting Started

This section guides you through setting up a simple project with massive.com/client-go.

First, make a new directory for your project and navigate into it:

mkdir myproject && cd myproject

Next, initialize a new module for dependency management. This creates a go.mod file to track your dependencies:

go mod init example

Then, create a main.go file. For quick start, you can find over 100+ example code snippets that demonstrate connecting to both the REST and WebSocket APIs.

Here's a working example that fetches daily aggregates for AAPL (with full pagination and trace support):

cat > main.go "        "          <- windows

Then, run go mod tidy to automatically download and install the necessary dependencies. This command ensures your go.mod file reflects all dependencies used in your project:

go mod tidy

Finally, execute your application:

go run main.go

REST API Client

[![rest-docs][rest-doc-img]][rest-doc]

To get started, you'll need to import two main packages.

import (
	"context"
	"fmt"
	"log"

	"github.com/massive-com/client-go/v3/rest"
	"github.com/massive-com/client-go/v3/rest/gen"
)

Next, create a new client with your API key.

c := rest.NewWithOptions("YOUR_API_KEY",
	rest.WithTrace(false),      // set true for full request/response logging
	rest.WithPagination(true),  // enables automatic pagination via iterator
)
ctx := context.Background()

Or create a client with a custom HTTP client implementation.

hc := http.Client{} // some custom HTTP client
c := massive.NewWithClient("YOUR_API_KEY", hc)

Using the client

After creating the client, making calls to the Massive API is simple. Most endpoints now use the generated *WithResponse methods:

// Example with custom params (note the Sort field requirement)
params := &gen.GetStocksAggregatesParams{
	Adjusted: rest.Ptr(true),
	Sort:     "asc",
	Limit:    rest.Ptr(120),
}