API
DEFINITION
An API (application programming interface) is a set of rules that lets a merchant's software communicate with a billing platform, such as Recurly, to create accounts, manage subscriptions, and process payments programmatically instead of through a manual web interface.
An API (application programming interface) is a set of rules that lets two pieces of software talk to each other, such as a billing system and a merchant's website or app.
In subscription billing, the API is the layer that lets a merchant's own systems create accounts, start and change subscriptions, issue invoices, and process payments without a person clicking through a web interface for every action. A request goes out from the merchant's application, the billing platform processes it, and a response comes back with the result, usually as structured data (commonly JSON).
Most subscription billing platforms, including Recurly, expose more than one API surface. There is typically a core API for accounts, subscriptions, and invoices, plus separate APIs for adjacent functions like commerce, revenue recognition, or checkout recovery. A merchant's engineering team picks the endpoints it needs instead of integrating with a single monolithic interface.
Why it matters
Manual billing does not scale. Once a subscription business has more than a handful of customers, someone has to automate account creation, plan changes, dunning, and invoicing, or the operational overhead grows faster than revenue. The API is what makes that automation possible. It lets engineering teams connect billing logic to the rest of the business, whether that is a signup form, a mobile app, an internal admin tool, or a data warehouse.
For Usage-based billing, real-time API calls to report usage events are often the only practical way to keep metering accurate. For high-volume businesses, API-driven automation is also what keeps Dunning and retry logic running without manual intervention.
Recurly's API documentation describes date-based versioning, so a request specifies the version it targets and existing integrations keep working as Recurly ships new functionality. Because the platform spans multiple API surfaces, such as subscription management, commerce, and revenue recognition, a merchant can integrate only the pieces relevant to its business rather than adopt an all-or-nothing platform.
Recurly's API can also handle billing information directly, which brings PCI DSS obligations into scope. A merchant that submits card data through the API is expected to complete the applicable PCI Self-Assessment Questionnaire, even when card data is only held in memory rather than stored. Teams that prefer to keep card data off their own servers entirely typically use Recurly.js or Recurly's hosted payment pages instead of passing raw card data through the API.
Recurly enforces default API rate limits of 400 requests per minute on sandbox sites and 1,000 requests per minute on production sites — production limits apply only to GET requests, so POST/PUT/DELETE calls (new subscriptions, account changes, etc.) don't count against the limit. Merchants running a large import or heavy test cycle can request a temporary increase from support. Recurly maintains official client libraries for Ruby, Node.js, Python, .NET, Java, PHP, and Go, plus native mobile SDKs for iOS and Android
How to use
A typical integration follows a similar pattern regardless of which billing API is involved:
Authenticate requests, usually with an API key or token scoped to a specific environment (sandbox or production).
Specify the API version being targeted, since most mature billing APIs use versioning so that new features do not break existing integrations.
Send requests to create or update core objects, such as accounts, subscriptions, plans, or invoices.
Handle the response, including error codes and messages, so the calling application can react appropriately, for example by retrying a failed payment or flagging a validation error to the user.
Account for pagination when listing large sets of records, and for rate limits when sending a high volume of requests in a short window.
Use webhooks or events alongside the API to stay in sync with state changes that start outside a direct request, such as a payment succeeding after a retry.
Benefits and examples
Automate the account and subscription lifecycle. Create an account and a subscription in the same call a customer completes checkout, instead of provisioning access by hand.
Build custom checkout and billing experiences. A signup flow, self-service portal, or in-app upgrade path can match the look and feel of the rest of the product while the API handles the billing logic behind it.
Support flexible billing scenarios. Handle future start dates, custom trial lengths, custom pricing, and predefined quantities without hardcoding a single billing pattern.
Integrate data and reporting. Pull subscription, invoice, and transaction data into a data warehouse or BI tool for finance and analytics.
Connect third-party and internal tools. Link billing data to a CRM, support tool, or internal dashboard so account status is visible wherever the team needs it.
Frequently asked questions
What is an API, in simple terms? An API is a defined way for one piece of software to request something from another, such as asking a billing system to create a subscription, without needing to know how that system works internally.
Do I need to use an API to run subscription billing? No. Many merchants manage billing entirely through a web-based admin interface. An API becomes necessary when a business wants to automate account creation, connect billing to its own application, or process a volume of changes too large to handle by hand.
What is the difference between an API and a webhook? An API call is a request your system sends to the billing platform to get information or make a change. A webhook is the reverse: the billing platform sends your system a notification when something happens, such as a payment failing or a subscription renewing. Most integrations use both.
Is an API integration difficult to build? It depends on the complexity of the billing scenarios involved. A basic integration that creates accounts and subscriptions is usually straightforward for a developer familiar with REST APIs. Integrations covering usage metering, proration, or multi-entity billing take more design work.
Does every subscription billing platform have the same API? No. Object names, authentication methods, versioning approaches, and available endpoints vary by vendor. Reviewing a platform's API reference documentation directly is the most reliable way to understand what it supports.
