Quickstart

You are done when can() shows used: 1 for a customer. Everything here runs on your backend. React pricing and checkout are covered in Next steps.

Get a secret key

Key prefix	Purpose	Use in
`sk_`	Secret key	Your backend only (Node.js, Python, Go)
`pk_`	Publishable key	Reading the public plan catalog from a browser

Never put an sk_ key in browser code. A pk_ key can only read the plan catalog, so it cannot send events.

You should have: a key that starts with sk_. Store it as NOZLE_SECRET_KEY in your backend environment.

Install the SDK

Node.js
Python
Go

npm install @nozle-js/node

pip install nozle-sdk

go get github.com/nozle-dev/nozle-go@v0.12.0

Create the client

The SDKs read NOZLE_SECRET_KEY when you do not pass a key.

Node.js
Python
Go

nozle.ts

import { Nozle } from '@nozle-js/node'

const nozle = new Nozle();

nozle_client.py

from nozle import Nozle

nozle = Nozle()

nozle_client.go

import nozle "github.com/nozle-dev/nozle-go"

client := nozle.New("") // an empty key reads NOZLE_SECRET_KEY

If it fails: Node.js throws Nozle: pass apiKey or set the NOZLE_SECRET_KEY environment variable, Python raises ValueError, and Go panics with nozle: apiKey must not be empty (pass it or set NOZLE_SECRET_KEY). The variable is not set in the process that runs your code.

Create a feature, a plan, a customer and a subscription

In the dashboard:

Create a metered feature with code api_calls.
Create a free plan with code quickstart_free. Add the feature with count aggregation and a limit of 10,000.
Create a customer with external ID customer_123.
Activate a subscription for that customer on quickstart_free.

See plans and subscriptions for the screens. This plan is free, so no payment method or cost rating is needed.You should see: customer_123 with one active subscription on quickstart_free.

Send your first event

The event name is the feature code, api_calls. Each event adds one to the count; tokens is metadata and does not change it.

Node.js
Python
Go

const transactionId = await nozle.track('customer_123', 'api_calls', {
  model: 'example-model',
  tokens: 1500,
});

transaction_id = nozle.track("customer_123", "api_calls", {
    "model": "example-model",
    "tokens": 1500,
})

err := client.Track(ctx, nozle.TrackParams{
  CustomerID: "customer_123",
  Event: "api_calls",
  Metadata: map[string]any{"model": "example-model", "tokens": 1500},
})
if err != nil { return err }

You should get: the event’s transaction ID back in Node.js and Python (a UUID string), and no error in Go. Without a subscription ID the SDK looks up the customer’s active subscription, so the call needs exactly one.If it fails:

What you see	Cause and fix
`No active subscription for customer 'customer_123'`	The customer has no active subscription. Finish the previous step.
`Customer 'customer_123' has 2 active subscriptions — pass subscriptionId explicitly`	Pass the subscription’s external ID in the event options.
A `401` response (Node.js: `track failed: 401 Unauthorized`)	The key is wrong or revoked. Create a new `sk_` key.
A `403` response (Node.js: `subscription lookup failed: 403 Forbidden`)	The key is a `pk_` key. Use an `sk_` key.

Read it back

Node.js
Python
Go

const result = await nozle.can('customer_123', 'api_calls');
// { allowed: true, remaining: 9999, limit: 10000, used: 1 }

result = nozle.can("customer_123", "api_calls")
# {"allowed": True, "remaining": 9999, "limit": 10000, "used": 1}

result, err := client.Can(ctx, "customer_123", "api_calls")
if err != nil { return err }
// result.Allowed == true; the used, limit and remaining fields are in the result

You should get: used: 1, limit: 10000 and remaining: 9999.If used is 0: events are processed asynchronously, so wait a few seconds and call can() again. If it stays at 0, check that the event name matches the feature code exactly (api_calls) and that the event was sent for the customer you are reading.can() is a point-in-time check and does not reserve quota. Treat a dependency error as an unavailable decision, not as a denial.

Next steps

Production integration checklist: event delivery, credits, cost rating and payments, before you accept customer traffic.
Show a pricing table and checkout with @nozle-js/react, and the merchant backend that creates checkout sessions.
SDK references: Node.js, Python, Go.
Billing concepts and entitlements.

Getting Started

Billing

Product Credits

Margin Intelligence

Entitlements

Get a secret key

Install the SDK

Create the client

Create a feature, a plan, a customer and a subscription

Send your first event

Read it back

Next steps

​Get a secret key

​Install the SDK

​Create the client

​Create a feature, a plan, a customer and a subscription

​Send your first event

​Read it back

​Next steps

Get a secret key

Install the SDK

Create the client

Create a feature, a plan, a customer and a subscription

Send your first event

Read it back

Next steps