REST vs SOAP: Which API Style Should You Use in 2025?

REST and SOAP are two approaches for building web APIs. REST dominates modern development, but SOAP still powers millions of enterprise integrations. This guide explains every meaningful difference with examples.

At a Glance

What Is REST?

REST (Representational State Transfer) is an architectural style defined by Roy Fielding in 2000. It uses HTTP as the transport and has six constraints:

1. Client–server — UI and data storage are separated
2. Stateless — each request contains all context; no session state on server
3. Cacheable — responses declare whether they can be cached
4. Uniform interface — resources identified by URLs, manipulated via representations
5. Layered system — client doesn't know if it's talking to origin or proxy
6. Code on demand (optional) — server can send executable code (e.g., JavaScript)

REST Request Example

GET /users/42 HTTP/1.1
Host: api.example.com
Authorization: Bearer eyJhbGci...
Accept: application/json

HTTP/1.1 200 OK
Content-Type: application/json

{
  "id": 42,
  "name": "Ana Kovač",
  "email": "ana@example.com"
}

REST CRUD Mapping

What Is SOAP?

SOAP (Simple Object Access Protocol) is a protocol with a strict XML envelope structure. It was designed for enterprise systems requiring formal contracts, built-in transactions, and advanced security.

SOAP Message Structure

<?xml version="1.0" encoding="UTF-8"?>
<soapenv:Envelope
  xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/"
  xmlns:usr="http://example.com/users">

  <soapenv:Header>
    <wsse:Security>
      <!-- WS-Security token here -->
    </wsse:Security>
  </soapenv:Header>

  <soapenv:Body>
    <usr:GetUserRequest>
      <usr:UserId>42</usr:UserId>
    </usr:GetUserRequest>
  </soapenv:Body>

</soapenv:Envelope>

SOAP Response

<soapenv:Envelope ...>
  <soapenv:Body>
    <usr:GetUserResponse>
      <usr:Id>42</usr:Id>
      <usr:Name>Ana Kovač</usr:Name>
      <usr:Email>ana@example.com</usr:Email>
    </usr:GetUserResponse>
  </soapenv:Body>
</soapenv:Envelope>

SOAP Fault (Error Response)

<soapenv:Body>
  <soapenv:Fault>
    <faultcode>soapenv:Client</faultcode>
    <faultstring>User not found: 42</faultstring>
    <detail>
      <usr:ErrorCode>USER_NOT_FOUND</usr:ErrorCode>
    </detail>
  </soapenv:Fault>
</soapenv:Body>

WSDL vs OpenAPI

SOAP requires a WSDL (Web Services Description Language) contract. REST typically uses OpenAPI (formerly Swagger), though it's optional.

WSDL snippet:

<wsdl:operation name="GetUser">
  <wsdl:input message="tns:GetUserRequest"/>
  <wsdl:output message="tns:GetUserResponse"/>
</wsdl:operation>

OpenAPI equivalent:

/users/{id}:
  get:
    summary: Get user by ID
    parameters:
      - name: id
        in: path
        required: true
        schema:
          type: integer
    responses:
      '200':
        description: User found
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/User'

Security Comparison

Key SOAP security advantage: WS-Security provides message-level security — the payload stays encrypted even if it passes through intermediaries (message brokers, ESBs). REST's HTTPS only protects the transport channel.

<!-- WS-Security header example -->
<wsse:Security>
  <wsse:UsernameToken>
    <wsse:Username>api-user</wsse:Username>
    <wsse:Password Type="PasswordDigest">dGVzdA==</wsse:Password>
    <wsse:Nonce>abc123</wsse:Nonce>
    <wsu:Created>2025-07-16T10:00:00Z</wsu:Created>
  </wsse:UsernameToken>
</wsse:Security>

Performance Comparison

REST is generally faster because:

1. Smaller payloads — JSON is ~30–50% smaller than equivalent XML
2. HTTP caching — GET responses can be cached by browsers, CDNs, proxies
3. Less parsing overhead — JSON parsing is faster than XML DOM parsing
4. No envelope overhead — no mandatory header/body wrapping

# Payload size comparison (same user object)

# REST JSON: 68 bytes
{"id": 42, "name": "Ana Kovač", "email": "ana@example.com"}

# SOAP XML: ~450 bytes (with envelope)
# <?xml version="1.0"?><soapenv:Envelope ...><soapenv:Body>
# <GetUserResponse><Id>42</Id><Name>Ana Kovač</Name>
# <Email>ana@example.com</Email></GetUserResponse>
# </soapenv:Body></soapenv:Envelope>

Caveat: Performance difference matters less at the network layer for large payloads. CPU cost of XML validation and signing is the bigger SOAP bottleneck.

Code Examples: Calling Both APIs

Calling a REST API (Python)

import httpx

# GET user
response = httpx.get(
    "https://api.example.com/users/42",
    headers={"Authorization": "Bearer eyJhbGci..."}
)
user = response.json()
print(user["name"])  # Ana Kovač

# POST create user
new_user = httpx.post(
    "https://api.example.com/users",
    json={"name": "Marko", "email": "marko@example.com"},
    headers={"Authorization": "Bearer eyJhbGci..."}
)
print(new_user.status_code)  # 201

Calling a SOAP API (Python with zeep)

from zeep import Client
from zeep.wsse.username import UsernameToken

client = Client(
    wsdl="https://api.example.com/UserService?wsdl",
    wsse=UsernameToken("api-user", "secret", use_digest=True)
)

# Call GetUser operation
response = client.service.GetUser(UserId=42)
print(response.Name)  # Ana Kovač

# Call CreateUser operation
result = client.service.CreateUser(
    Name="Marko",
    Email="marko@example.com"
)
print(result.Success)  # True

Calling a SOAP API (Java with JAX-WS)

// Auto-generated stub from WSDL (wsimport or wsdl2java)
UserService service = new UserService();
UserPortType port = service.getUserPort();

// Set WS-Security credentials
BindingProvider bp = (BindingProvider) port;
bp.getRequestContext().put(BindingProvider.USERNAME_PROPERTY, "api-user");
bp.getRequestContext().put(BindingProvider.PASSWORD_PROPERTY, "secret");

GetUserRequest request = new GetUserRequest();
request.setUserId(42);

GetUserResponse response = port.getUser(request);
System.out.println(response.getName()); // Ana Kovač

WS-* Standards (SOAP Extensions)

SOAP has an ecosystem of WS-* (Web Services) specifications:

REST has no equivalent built-in standards — you implement these at the application layer.

Where REST Wins

Where SOAP Wins

Full Comparison Table

REST vs SOAP vs GraphQL vs gRPC

Decision Guide

Need to integrate with existing SOAP/WSDL system?
→ SOAP

Need distributed transactions across services?
→ SOAP (WS-AtomicTransaction)

Building a public API (web or mobile)?
→ REST

Building a microservices backend?
→ REST or gRPC

Frontend needs flexible data fetching?
→ GraphQL

Performance-critical internal services?
→ gRPC

Everything else?
→ REST

Migrating from SOAP to REST

If you're modernizing a SOAP service, a common approach is the anti-corruption layer pattern:

# REST façade in front of legacy SOAP service
from fastapi import FastAPI
from zeep import Client

app = FastAPI()
soap_client = Client(wsdl="https://legacy.example.com/UserService?wsdl")

@app.get("/users/{user_id}")
def get_user(user_id: int):
    # Translate REST request to SOAP call
    soap_response = soap_client.service.GetUser(UserId=user_id)
    
    # Translate SOAP response to REST JSON
    return {
        "id": user_id,
        "name": soap_response.Name,
        "email": soap_response.Email
    }

This lets new clients use REST while the SOAP backend stays unchanged.

Common Mistakes

REST vs SOAP vs Related Terms

FAQ

Q: Is SOAP dead?
No. Millions of SOAP services run in banking, healthcare, government, and enterprise ERP systems. New development rarely chooses SOAP, but existing SOAP integrations will run for decades.

Q: Can REST be as secure as SOAP?
Yes, with HTTPS + OAuth 2.0 + JWT + proper implementation, REST is secure for most use cases. SOAP's WS-Security advantage matters when you need message-level encryption that survives intermediaries, which is rare outside highly regulated industries.

Q: Which is faster: REST or SOAP?
REST is typically 30–50% faster in practice because JSON payloads are smaller and cheaper to parse than XML. The difference matters most at high request volumes (millions/day).

Q: Does REST require JSON?
No. REST can use XML, HTML, plain text, or any format. JSON is used because it's lightweight and JavaScript-native, not because REST requires it.

Q: Can SOAP use HTTP GET?
Technically yes, but SOAP almost always uses HTTP POST because the entire request is in the XML body. There's no concept of URL-based resources.

Q: Should I learn SOAP in 2025?
Learn REST first — you'll use it in almost every job. Learn SOAP only if you work in finance, healthcare, enterprise integration, or need to maintain legacy systems. Basic SOAP knowledge is useful; deep WS-* expertise is only needed for specialist roles.