> ## Documentation Index
> Fetch the complete documentation index at: https://docs.getlago.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Welcome to Lago

> Lago is an open-source software for metering and usage-based billing. It's the best alternative to Chargebee, Recurly or Stripe Billing for companies that need to handle complex billing logic.

This library will allow you to build an entire billing system from scratch. Lago is a real-time, event-based solution made for usage-based billing, subscription-based billing, and all the nuances of pricing in between.

You can use the [self-hosted version](/guide/lago-self-hosted/docker) to deploy Lago on your existing infrastructure or [request access to Lago Cloud](https://getlago.com/book-a-demo) to start using our solution immediately.

## Five-step billing workflow[](#five-step-billing-workflow "Direct link to heading")

### 1. Usage ingestion[](#1-event-ingestion "Direct link to heading")

[Events](/guide/events/ingesting-usage) provide information about your customers'
consumption, with the highest level of granularity. Any product feature for
which you want to charge your customers should correspond to a specific event.
An event can be triggered by an action or can be sent periodically. Lago is able
to ingest events at scale while preventing duplicates.

### 2. Metrics aggregation[](#2-metrics-aggregation "Direct link to heading")

The aggregation process consists of converting events into
[billable metrics](/guide/billable-metrics/create-billable-metrics). There are 4 aggregation types:

| Aggregation    | Description                                                                                            | Type                 |
| -------------- | ------------------------------------------------------------------------------------------------------ | -------------------- |
| `COUNT`        | Counts the number of times an incoming event occurs                                                    | Metered              |
| `COUNT_UNIQUE` | Returns the number of unique values of a predefined property for incoming events                       | Metered or Recurring |
| `LATEST`       | Returns the latest value of a predefined property for incoming events                                  | Metered              |
| `MAX`          | Returns the maximum value of a predefined property for incoming events                                 | Metered              |
| `SUM`          | Calculates the sum of a predefined property for incoming events                                        | Metered or Recurring |
| `WEIGHTED SUM` | Calculates the sum of a predefined property for incoming events prorated based on time used per period | Metered or Recurring |

### 3. Pricing and packaging[](#3-pricing "Direct link to heading")

Creating [plans](/guide/plans/overview) allows you to define how much your customers
should pay for using your product. You can then combine plans and billable
metrics to implement any billing model (i.e. subscription-based, usage-based, or
hybrid). Billable metrics may be priced differently depending on the associated
plan.

### 4. Invoicing[](#4-invoicing "Direct link to heading")

Lago automatically generates [invoices](/guide/invoicing/overview) for each customer
according to the plan model: the subscription fee can be billed at the beginning
or at the end of the billing period while usage-based charges are always
calculated at the end of the billing period. Invoices include fees, taxes and
customer information.

### 5. Payments[](#5-payments "Direct link to heading")

When an invoice is emitted and finalized, it's ready for payment collection.
Connect payment providers through [native integrations](/guide/payments/payment-providers) or
trigger payments on any PSPs using the invoice payload created by Lago.