One of the differences between REST and SOAP is that REST is lighter than SOAP. What does it mean when they say REST APIs are lighter than SOAP APIs? How is JSON lighter than XML?

When a developer talks about something's "weight" (heavier or lighter), we're referring to the resources it consumes. SOAP requires substantially more memory and bandwidth than a JSON string of the same representation. To make matters worse, SOAP is an extension of XML, adding even more bloat to the entire process. To give you a simple comparison, consider these two functionally identical requests:

SOAP (Create Call)

POST /services/Soap/u/44.0

Host: mydomain.my.salesforce.com

Content-Type: text/xml; charset=utf-8

Content-Length: nnn

SOAPAction: ""



<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:urn="urn:enterprise.soap.sforce.com" xmlns:urn1="urn:sobject.enterprise.soap.sforce.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

  <soapenv:Header>

    <urn:SessionHeader>

      <urn:sessionId>[sessionId retrieved from the login() call]</urn:sessionId>

    </urn:SessionHeader>

  </soapenv:Header>

  <soapenv:Body>

    <urn:create>

      <urn:sObjects xsi:type="urn1:Account">

        <Name>Sample Inbound Account One</Name>

      </urn:sObjects>

    </urn:create>

  </soapenv:Body>

</soapenv:Envelope>

REST (Equivalent to above)

POST /services/data/44.0/sobjects/Account

Host: mydomain.my.salesforce.com

Authorization: Bearer [sessionId retrieved from a login call]

Content-Type: application/json; charset=utf-8

Content-Length: nnn



{ "Name": "Sample Inbound Account One" }

And this is with just one field. The more fields and records used, the more SOAP will fall behind in efficiency compared to REST. Most methods that you can use in SOAP can also be used in REST, and vice versa. The heavy weight of SOAP can make requests take longer in areas where bandwidth is limited, and may cause low-memory devices to fail from a lack of memory sooner. Overall, when resources are at a premium, you want to use REST.

The reason why you'd use SOAP at all is because you're using some application or language that only "understands" SOAP, or makes REST obnoxiously hard to use. For example, in some languages, you import a "WSDL" and calling the service literally only takes a few lines of code, while the same thing in REST requires importing a JSON parser, an HTTPS library, jump through some encoding hoops, etc. In other languages, the opposite is true: there is no SOAP support (but SOAP is really just a special case of normal HTTP calls), so SOAP is harder to implement and error prone, while REST would be naturally supported.