With OpenAPI contracts, you can create new API code, manage live traffic and logs, and generate documentation, client SDKs, and MOQ servers. The specification can also perform API governance checks and run API tests. In this blog, we'll explore the history of OpenAPI, OpenAPI meaning, how it works, best practices, limitations, and more.
Let's get into it.
What is OpenAPI Specification?
OpenAPI is a standard specification for creating and deploying software apps that can interact with RESTful APIs. It was previously known as Swagger. The OpenAPI schema, which relies on JSON to describe the APIs’ underlying data, is based on this schema.
What does Open API mean? Put simply, it’s an API available to the public on the internet that you can use to communicate with other apps, databases, OS, information systems, and software. Some OpenAPIs may need an authentication or registration key for use.
How is OpenAPI’s Structure?
OpenAPI format: we will not discuss the nuances of JSON in this blog post, but we will tell you this. JSON is a way to represent your API data as key-value pairs.
In a legacy specification, you must write the title and use a title style on the cover page. An API contains much information, such as operations, methods, and responses. These properties are documented within key-value pairs that adhere to the OpenAPI structure.
Although JSON is the default format for OpenAPI, you can represent OpenAPI as YAML. If you are using the OpenAPI specification as a JSON object, you can define data types. The main primitives will be numbers, booleans, integers, and strings.
You can declare data type formats by using the modifier property format. You can declare an integer as an int64 or int32 format. You can change them to float, double, or define strings as date, DateTime, and password formats.
So far, here's what you need to know about the OpenAPI structure: a JSON object is an OpenAPI specification. Your API's properties will be described as sets of key-value pairs, data types defined by the broad JSON specification.
Here is an OpenAPI template showing the overall structure and our discussion. The first set of brackets defines the document object, which has all the OpenAPI properties, as shown in the screenshot.
This is the basic structure we are showing. Some high-level sections are needed, but some are not. An OpenAPI spec or document will have the following sections, but not all of them will be included: info, servers, paths, OpenAPI, components, security, tags, and external docs.
So, in the case of the legacy specification, the underlying source code changes and the document updates. Legacy specification documents will require you to update Word documents whenever system changes are made manually.
These changes cannot be tracked automatically or reflected in the main document. Thus, the OpenAPI specification is dynamic. When you read the API specification, you also learn about the types of requests you can send out and what responses you can get back from the API.
How Does the OpenAPI Specification Work?
The OpenAPI specification provides a language-agnostic interface to RESTful APIs. Using the HTTP protocol, data can be transmitted across platforms and systems.
It enables services written in different languages to interact seamlessly with each other.
The OpenAPI specification defines how clients will engage with it. The client won't have to read any source code, as the OpenAPI specification conforms to the RESTful architecture.
The Technical Steering Committee now manages OpenAPI. The committee actively accepts community suggestions and sends release updates based on that feedback.
Consider a legacy specification document you must read in Microsoft Word format. This document provides a broad context about systems and how different components and services interact. The structure of these documents can vary. If the specification changes, you will have to update the document and manually change each section. You will also need to learn about the legacy specification to make updates.
In contrast, the OpenAPI specification is a more dynamic document. It strictly conforms to a structure but updates itself automatically, so you don't have to intervene manually.
History of OpenAPI
The OpenAPI specification was first developed in 2009 by Tony Tam, an engineer at Wodnik. In 2011, the Swagger specification became a part of the Swagger toolkit, and the Wordnik dictionary team launched it. The Swagger toolkit included Swagger Codegen, an annotations library, and the Swagger UI. These were used to create OpenAPI's documentation and generate SDKs. The Swagger Toolkit's second version was released around 2014, along with the Swagger 2.0 specification. This version came with the editor and supported editing Swagger 2.0 documents in YAML and JSON formats. In 2015, the Swagger 2.0 specification was donated.
It was handed over to the OpenAPI initiative, which came directly under the Linux foundation. The OpenAPI initiative was run by a group of companies: Google, IBM, Intuit, Capital One, Apigee, SAP, Postman, Microsoft, and Salesforce. They shared the goal of making the OpenAI specification vendor-neutral and open-sourced in its description format.
Differences between OpenAPI vs Swagger
If you are confused between OpenAPI and Swagger, just know that Swagger 2 is just an earlier version of OpenAPI 3. Both Swagger and OpenAPI use JSON and YAML formats. They rely on the JSON schema to describe your API's underlying data. But they use different versions of the JSON schema. The info block is also standard for both of these specifications.
However, OpenAPI 3.1 recently added a summary. These APIs have several new properties, such as license, identifier, and summary. They also come with an SPDX license expression. All these APIs support complex workflows across the API lifecycle.
Now let's discuss the differences between OpenAPI and Swagger:
One of the main differences is how users define centralized reusable components. With Swagger 2.0, you must use definitions, parameters, responses, and the securityDefinitions fields.
Swagger doesn’t have this, but OpenAPI 3.1 added reusable examples, headers, and pathItems.
You also get expanded support for the JSON schema. OpenAPI 3.1 has brought in consistency when it comes to defining every piece of data. You can find these elements under shared data models located under components.schemas. Note that different versions of OpenAPI use different versions of the JSON schema.
OpenAPI 3 enables asynchronous communication, where the API provider defines operations, but the API consumer does the implementation. For instance, callbacks, introduced in OpenAPI 3.0, can be specified at the operation level and are called by the provider when a long-running task is completed. OpenAPI 3.1 added webhooks, allowing the provider to invoke a particular operation due to an event happening independently. They don’t have to wait for some previous action from the consumer. All this flexibility permits APIs to deal with operations and events in a much more dynamic, non-blocking fashion.
How is OpenAPI’s Security?
You can learn more about OpenAPI’s security by exploring the Security Scheme Object.
OpenAPI currently supports these security types: HTTP authentication, OAuth 2.0, API Keys, Mutual TLS, and OpenID Connect.
What are OpenAPI’s Limitations?
OpenAPI has some limitations. It doesn't use a hierarchical structure, and data model inheritance features are unavailable. OpenAPI can only be used to describe RESTful APIs.
You won't get any server templating features, and the OpenAPI 3.0 user interface also doesn't support referencing request body components. The IBM App Connect Enterprise won't work with parsing or mapping complex type parameters. You can't convert WSDL-defined SOAP services into an OpenAPI 3.0 API, so SOAP service conversion is non-existent.
You also don't get support for callbacks and links, and OpenAPI specifications don't let you name ruleset parameters as requests or responses. You may encounter execution errors with short numbers.
You may encounter restrictions when using OpenAPI with tools and hosted transparency decision services. Also, Using OpenAPI-based clients may cause you to encounter incorrect behaviors in some of OpenAPI's reference tools.
If you switch from OpenAPI 2.0 to 3.0, the Open API definitions for security will change between versions. You will encounter authentication errors if you don't update these definitions, especially when invoking new rulesets. You will have to diagnose these problems yourself.
Why Are Companies Using OpenAPI?
Companies use OpenAPI because it is portable and simple. It is a common language for communicating with clients and servers and is highly compatible with different programming languages.
If you think OpenAPI's documentation is unclear enough, refer to the API Blueprint. However, it's important to note that the API Blueprint is not well-known, so its adoption rate is relatively low. You can integrate the API Blueprint across your entire API lifecycle, but it's challenging because its main focus is documentation.
OpenAPI will grow in its adoption and be a long-term viable standard for describing APIs in the coming years.
Why is OpenAPI so popular? It is one of the most widely used and well-known frameworks. It also supports two other formats: API Blueprint and the RAML format. OpenAPI is often dubbed the industry standard.
OpenAPI Best Practices
OpenAPI takes two approaches: code-first and design-first. In the former, you implement the API in the code. You use code comments annotations or write the description from scratch. As a developer, you won’t have to learn new languages.
In the design-first approach, you write the description first. The code comes with a skeleton that you can flesh out. When coding the API, consider avoiding writing unintuitive or unclear descriptions.
You can use different validation tools to test your API code and verify. Run these tools as a part of your continuous integration process. You can detect any deviations or abnormal behaviors associated with code changes promptly that way.
Here are some other OpenAPI best practices that you should be aware of:
You can maintain production-grade enterprise clients with OpenAPI. Keep a single source of truth and move repeated codes to standard functions. Add your OpenAPI descriptions to SourceControl and drive great automation. You can use them to generate boilerplates, run unit tests, and render documentation.
Handwritten OpenAPI descriptions may work best for your team. They are faster than writing digital text documents, so if you are strapped for time, consider making this productivity switch. However,t if you write documentation in text files, use the OpenAPI GUI or text editors. You can also create your descriptions using a DSL and hand-tune the resulting file.
Follow the DRY principle, and don’t repeat yourself. Don’t reuse descriptions; instead, split them into several documents. You can organize things using tags.
If you need tips on external practices, refer to the API Stylebook. It’s a valuable resource that provides design guidelines for any industry.
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Conclusion
We hope our guide served as a valuable introduction to OpenAPI. Open APIs allow your users to access network-level services. Learning about them and how they work is worth the time and effort. Use them across different verticals and see the magic happen.
OpenAPI Frequently Asked Questions
What is the primary use of OpenAPI?
It’s a framework that allows you to carry data across every stage of the API lifecycle. It can streamline interactions between RESTful APIs.
Which industries are using OpenAPI?
OpenAPI is popular in industries such as IT and telecom, banking and finance, healthcare, media and entertainment, and energy and utilities. It is freely available to the public and compatible with most apps and services.
What can I do with OpenAPIs?
You can build digital finance portals, create online healthcare services, and unlock new revenue streams through custom solutions. OpenAPIs can foster more innovation for your business and enhance communications between services. They also facilitate greater interoperability and integration between different business systems.
Can I test and deploy new services with OpenAPIs?
Yes! You can also reduce the time to market for new products. These flexible and scalable APIs provide standardized access and interfaces to pre-built functionalities. You can also rapidly prototype your concepts and collaborate with other developers on OpenAPI projects.