SOAP vs REST API — Everything You Need to Know

6 min readJul 28, 2021

When I started reading up on Application Programming Interfaces or APIs, I found several articles debating on whether choosing SOAP was the right choice or was it REST. Nearly every article I came across covered different aspects, whereas I was looking for one source with all the information compiled in brief.

Hence, here’s the full comparison of SOAP and REST API. This is everything you need to know before you decide which of these suit your needs better.

Abbreviation:

SOAP : Simple Object Transfer Protocol

REST : Representational State Transfer

Founders:

SOAP : Dave Winer, Don Box, Bob Atkinson, and Mohsen Al-Ghosein for Microsoft (1998)

REST : Roy Fielding and team (2000)

Type:

SOAP : protocol

REST : architectural pattern

Business Logic is exposed using:

SOAP : uses services interface, WSDL file provides client with necessary information

REST : uses uniform resource identifiers (URI)

Bandwidth and Resource use:

SOAP : requires more usage due to large amount of data transfer

REST : requires less usage as data transfers mostly consist of JSON messages which are significantly smaller

Security Measures:

SOAP : defines its own security (SSL and WS-Security), greater security measures taken as compared to REST

REST : inherits its security measures from underlying transport (SSL and HTTPS)

Permitted Data Formats:

SOAP : only XML is supported

REST : XML, JSON, HTML, Plain Text, etc., are supported (JSON is preferred format)

Java API used:

SOAP : JAX-WX (Java API for XML based web services in SOAP)

REST : JAX-RS (Java API for RESTful Web Services)

Standards:

SOAP : strictly defined standards, only XML and HTTP used

REST : no official standards, uses multiple standards like HTTP, JSON, URL, XML, etc.

Elements/Constraints:

SOAP API elements -

Envelope
Header
Body
Fault

REST API constraints -

Uniform Interface
Stateless
Cacheable
Client-Server
Layered System
Code on Demand

Request Messages:

SOAP request message types -

1. GET — Read or retrieve data

2. POST — Add new data

3. PUT — Update data that already exists

4. DELETE — Remove data

5. HEAD — identical to GET but without response body

6. OPTIONS — describe the communication options for the target resource

7. TRACE — performs a message loop-back test along the path to the target resource

8. PATCH — applies partial modifications to a resource

REST request message types -

1. GET — Read or retrieve data

2. POST — Add new data

3. PUT — Update data that already exists

4. DELETE — Remove data

Description Language used:

SOAP API : uses Web Services Description language to describe functionalities

REST API : uses Web Application Description Language to describe functionalities

Advantages:

Benefits of SOAP over REST API -

1. Language, Platform and Transport independent (REST requires use of HTTP, SOAP server can be based on JAVA and client can be on .NET, PHP etc. and vice versa.)

2. WSDL document provides contract and technical details of the web services for client applications without exposing the underlying implementation technologies.

3. SOAP protocol is universally accepted, so it’s an industry standard approach with many easily available open source implementations.

4. Works well in distributed enterprise environments (REST assumes direct point-to-point communication)

5. Standardised protocol

6. Provides significant pre-build extensibility in the form of the WS* standards

7. Built-in error handling

8. Automation when used with certain language products

9. Recommended for ACID compliant transactions

Benefits of REST over SOAP API -

1. Uses easy to understand standards like swagger and OpenAPI Specification 3.0

2. Smaller learning curve
Efficient (SOAP uses XML for all messages, REST mostly uses smaller message formats like JSON)

3. Fast (no extensive processing required) and better performance

4. Closer to other Web technologies in design philosophy

5. Greater variety of data formats allowed

6. Better support for browser clients (due to use of JSON, HTTP)

7. Easy scalability

8. Amazon, Yahoo, Ebay, Google, etc., use REST API.

Disadvantages:

Drawbacks of SOAP API -

1. Tight coupling between server and client applications (SOAP is based on contract)

2. Slow performance due to large payload (due to XML format)

3. Can’t be easily tested on browser easily

4. Only XML is used (JSON and other lightweight formats not supported)

5. Client stub-classes need to be generated every time there is a change made in server side contract

Drawbacks of REST API -

1. Lacks security measures

2. Lack of stateful methods

3. Hard to handle APIs

4. No asynchronous calls (REST works on HTTP)

5. No contract between client and server applications (communication must be through documentation and emails)

6. Sessions can’t be maintained

Best Practices:

SOAP API best practices -

1. Make sure process records are called in batches.

2. Use incremental processing

3. Check for Data Skew impact

4. Check for parent roll-up summary fields

5. Keep note of Operations that cause cascading changes

REST API best practices -

1. Accept and respond with JSON

2. Use nouns instead of verbs in endpoint paths

3. Name collections with plural nouns

4. Nesting resources for hierarchical objects

5. Handle errors gracefully and return standard error codes

6. Allow filtering, sorting, and pagination

7. Maintain Good Security Practices

8. Cache data to improve performance

9. Versioning the APIs

When to use which API:

SOAP API must be used when -

1. Asynchronous processing and invocation is required

2. Formal contract requirement where client and server agree on exchange format

3. Stateful operations (contextual information and conversational state management) are required

REST API must be used when -

1. Bandwidth and resources are limited

2. Stateless CRUD operations are required

3. Caching is required

Interoperability between REST and SOAP APIs:

SOAP : cannot make use of REST architectural pattern since SOAP is a protocol

REST : can make use of SOAP protocol for web services since it is an architectural pattern

General Preference:

SOAP : generally less preferred

REST : generally more preferred

Note :

This article is not sponsored and is purely based on the author’s opinions and personal experience on the journey of learning. None of the links provided here are affiliate links and are provided only for the purpose of learning.

The author is a student completing an Engineering Degree in Computer Science with Specialization in Cloud Technology and Mobile Applications.

Check out this article on my Personal Blog for a side-by-side comparison: SOAP vs REST API — Everything You Need to Know

Check Out this link for a table of comparison and differences between SOAP and REST API :