APIs are the backbone of modern software development, enabling smooth communication between systems. Two terms often discussed in this context are REST API and OpenAPI. While they are related, they serve different purposes.
In this guide, we’ll break down:
- What REST APIs and OpenAPI really are with technical examples
- Key differences and why you shouldn’t treat them as alternatives
- How BoldSign leverages both for seamless e-signature integrations
What is a REST API?
A representational state transfer application programming interface (REST API) is a set of architectural principles for designing networked applications. REST APIs use standard web protocols, primarily HTTP, to enable communication between a client and a server.
REST APIs rely on six architectural principles:
- Client-server: Separates the client (user interface) from the server (data storage).
- Stateless: Each request contains all the information needed, with no server-side session storage.
- Cacheable: Responses can be cached to improve performance.
- Uniform interface: Standardized methods like GET, POST, PUT, and DELETE can be used to interact with resources.
- Layered system: The architecture can be composed of layers, each with specific functionality.
- Code on demand (optional): Servers can send executable code to clients.
How REST APIs work
REST APIs function by allowing clients to send HTTP requests to a server, which responds with data, typically in JSON or XML format. For example:
- A client sends a GET request to https://api.example.com/users/123 to retrieve user data.
- The server processes the request and returns a JSON response: {“id”: 123, “name”: “John Doe”}.
Each method does something different:
- GET retrieves data.
- POST creates new data.
- PUT updates existing data.
- DELETE removes data.
When to use a REST API
REST APIs are ideal for:
- Web and mobile applications: When you need to fetch or manipulate data over HTTP, such as in e-commerce or social media apps, REST APIs are recommended.
- Scalable systems: The stateless nature of REST APIs makes them suitable for distributed systems.
- Public APIs: Use REST APIs when exposing services to third-party developers, since REST is widely understood.
- Microservices: REST is a natural fit for microservices architectures due to its lightweight nature.
Pitfalls to avoid
While REST is powerful, watch out for these common issues:
- Poor versioning: Breaking changes can disrupt clients if versions aren’t handled properly.
- Over-fetching or under-fetching: Poorly designed endpoints may return too much or too little data, impacting performance.
- Security flaws: Inadequate authentication or authorization can expose data
- Unclear documentation: Without good documentation, even the best-designed REST API can be hard to use
- Ignoring error handling: Inconsistent error responses like non-standard HTTP status codes confuse developers.
What is OpenAPI?
Now, imagine you’re handed a REST API but you have no clue how it works. That’s where OpenAPI saves the day. OpenAPI isn’t an API itself—it’s a blueprint that explains a REST API in a clear, structured way using a file in JSON or YAML format. Think of it as a user manual that tells developers exactly how to use the API.
The OpenAPI specification enables developers to:
- Define API endpoints, parameters, and schemas.
- Generate interactive documentation like Swagger UI.
- Automate testing, client SDK generation, and server stubs.
OpenAPI in action
Here’s a small snippet of an OpenAPI specification:
openapi: 3.0.3
info:
title: Sample API
version: 1.0.0
paths:
/users/{id}:
get:
summary: Get user by ID
parameters:
- name: id
in: path
required: true
schema:
type: string
responses:
'200':
description: Successful response
content:
application/json:
schema:
type: object
properties:
id: { type: string }
name: { type: string }
When to use OpenAPI
OpenAPI is essential when:
- You want clear, standardized documentation for your REST APIs.
- You need to auto-generate client/server code.
- You’re collaborating with multiple teams or third parties.
- You require API testing, mocking, or automation.
- You’re building developer-friendly APIs.
Pitfalls to avoid
- Overcomplicating schemas: Overly complex OpenAPI files can be hard to maintain.
- Outdated documentation: Failing to update the specification when the API changes leads to inconsistencies.
- Ignoring tooling: Not leveraging OpenAPI-compatible tools like Swagger Editor misses automation benefits.
- Poor structure: Unorganized or incomplete specs reduce usability for developers.
Key differences between OpenAPI and REST API
Let’s look at the key differences between these two options.
| Feature | REST API | OpenAPI |
|---|---|---|
| Definition | The actual system that connects apps | A guide that describes how the API works |
| Purpose | Sends and receives data (like JSON) | Creates a roadmap for using the API |
| Data Format | Uses HTTP methods and URI structures | Uses YAML and JSON to define API structure |
| Tooling | Postman, cURL | Integrates with tools like Swagger UI |
| Automation | Manual setup required | Enables auto-generation of API docs, client SDKs, and testing tools |
| Use Case | Building and deploying APIs | Describing, testing, documenting, and managing APIs |
How BoldSign uses REST API and OpenAPI
The BoldSign e-signature platform leverages both REST APIs and OpenAPI to deliver a smooth developer experience.
REST API for core e-signature workflows
The BoldSign REST API is the engine behind its e-signature features. It lets businesses automate tasks like:
- Sending documents for signing with a POST request to /documents/send.
- Checking document details and status with a GET request to /document/properties.
- Update identities with PUT request to v1/senderIdentities/update.
- Automate reminders.
- Send webhook notifications or real-time signing events like a document completed sample payload.
Example request:
curl -X 'POST' \ 'https://api.boldsign.com/v1/document/send' \
-H 'accept: application/json' \
-H 'X-API-KEY: {your API key}' \
-H 'Content-Type: multipart/form-data' \
-F 'Signers={
"Name": "sdc",
"EmailAddress": "alexgayle@cubeflakes.com",
"SignerType": "Signer",
"FormFields": [
{
"Id": "string",
"Name": "string",
"FieldType": "Signature",
"PageNumber": 1,
"Bounds": {
"X": 50,
"Y": 50,
"Width": 1,
"Height": 1
},
"IsRequired": true
},
"Locale": "EN"
OpenAPI for effortless integration
BoldSign provides an OpenAPI specification to:
- Understand how to use our endpoints.
- Generate SDKs in multiple languages like Python, C#, Node.js, PHP, and Java.
- Power interactive documentation so developers can explore and test endpoints via Swagger UI.
- Test API requestswithout writing code.
Takeaways
- REST API: The system that sends and receives data.
- OpenAPI: The blueprint that documents it.
- Use REST for building APIs.
- Use OpenAPI to document and automate APIs.
- The best results come from combining both tools, like BoldSign does.
Conclusion
Understanding the difference between OpenAPI and REST API is key to choosing the right approach for your needs. Platforms like the BoldSign e-signature API, OpenAPI, and REST API enable smooth integration for electronic signature workflows.
Try it out today—sign up for a free BoldSign sandbox account and start integrating e-signatures into your application.
Share your thoughts below! To learn more about the BoldSign API, explore our developer documentation. For any questions or assistance, feel free to reach out via our support portal.
Related blogs
- REST API vs SDK: Which is Best for eSignature Integration
- API Key Vs. OAuth – How to Choose the best Authentication
- Integrate BoldSign API in MAUI Mobile App for smooth eSign
Note: This blog was originally published at boldsign.com
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