SOAP vs REST API: Comparison

APIs have become foundational to modern enterprise operations. They power customer facing applications, partner integrations, cloud migrations, and internal automation at scale. Gartner estimates that APIs now underpin the majority of digital business initiatives, with API driven architectures acting as a primary enabler for cloud adoption, SaaS integration, and platform based business models. As a result, architectural choices such as SOAP vs REST are no longer confined to engineering teams. They directly influence speed, cost, risk, and long term scalability.

Despite the rise of REST, SOAP remains deeply embedded in enterprise environments. Gartner and Red Hat research consistently note that large organizations continue to rely on SOAP APIs for mission critical systems such as payments, billing, identity management, and regulatory reporting, where strict contracts and reliability are prioritized. At the same time, REST APIs dominate modern development. Postman’s State of the API Report shows that REST remains the most widely used API style, driven by mobile applications, microservices, and cloud native workloads that demand faster iteration and simpler integration.

This coexistence creates a hybrid reality for enterprises. SOAP APIs provide stability and governance but are often perceived as slow, rigid, and costly to evolve. REST APIs offer agility and developer productivity, yet introduce rapid API sprawl and inconsistent security controls when not governed properly. According to IBM’s Cost of a Data Breach Report, application layer failures continue to be among the most expensive breach vectors, reinforcing that modernization without security alignment increases business risk.

From a business perspective, the pain points are clear. Digital transformation initiatives stall when legacy SOAP services cannot support modern use cases. At the same time, ungoverned REST adoption leads to undocumented endpoints, fragmented authentication models, and expanding attack surfaces. Many organizations struggle to test, secure, and monitor both architectures consistently, especially during migration phases where SOAP and REST APIs operate side by side.

Security further amplifies these challenges. SOAP APIs often depend on heavyweight, standards driven security mechanisms, while REST APIs rely on tokens, custom authorization logic, and application level controls. Without unified visibility and continuous testing across both styles, organizations inherit blind spots that surface later as breaches, compliance gaps, or delayed releases.

Understanding the difference between SOAP and REST APIs is therefore not just a technical comparison. It is a strategic decision with direct impact on integration speed, security posture, and operational resilience. As enterprises modernize their API ecosystems, choosing how to design, test, and secure SOAP and REST APIs becomes central to sustaining growth without increasing risk.

What is SOAP?

SOAP, or Simple Object Access Protocol, is a messaging protocol designed to enable structured, standardized communication between applications over a network. Unlike lightweight API styles, SOAP was built for enterprise environments where reliability, strict contracts, and formal governance are required. It defines a rigid framework for how messages are formatted, transmitted, and processed, ensuring that both the sender and receiver follow the same rules at all times.

At its core, a SOAP API exchanges messages using XML. Every request and response follows a predefined structure that includes an envelope, header, and body. This structure enforces consistency and predictability, which is why SOAP has historically been used in industries such as banking, telecommunications, healthcare, and government systems where errors, ambiguity, or data loss are unacceptable.

SOAP APIs are typically described using a WSDL, or Web Services Description Language file. The WSDL acts as a formal contract that defines available operations, input and output schemas, data types, and communication rules. This contract driven model allows client and server implementations to be generated automatically and validated rigorously before deployment.

From an architectural standpoint, SOAP is protocol agnostic. While it is most commonly used over HTTP and HTTPS, it can also operate over SMTP and other transport mechanisms. This flexibility made SOAP attractive in earlier enterprise integration scenarios where systems spanned multiple networks and communication standards.

Security is a defining characteristic of SOAP. It commonly relies on WS-Security standards that support message-level encryption, digital signatures, and identity assertions. These controls operate within the message itself rather than relying solely on the transport layer, making SOAP well suited for scenarios that demand non-repudiation, transactional integrity, and compliance-driven security models.

In the context of the broader soap vs rest discussion, SOAP represents a contract first, standards heavy approach to API design. It prioritizes predictability, governance, and formal validation over flexibility and speed. While this model introduces overhead and complexity, it continues to underpin many mission critical enterprise systems where stability and compliance outweigh the need for rapid iteration.

Understanding what a SOAP API is, and why it was designed this way, is essential before comparing it to REST APIs or evaluating the difference between SOAP and REST API architectures in modern environments.

How does SOAP API Testing work?

SOAP API testing focuses on validating both the structure and the behavior of SOAP based services against their formally defined contracts. Because SOAP APIs are highly standardized and rely on XML schemas and service definitions, testing is centered on correctness, predictability, and compliance across every interaction.

At the foundation of SOAP API testing is the WSDL. The WSDL acts as the authoritative contract that defines available operations, message formats, data types, and communication rules. Testing begins by validating that the service strictly adheres to this contract. Requests and responses are checked to ensure they conform exactly to the expected schemas, namespaces, and data structures. Any deviation from the contract is treated as a defect rather than an acceptable variation.

SOAP messages are encapsulated within XML envelopes that include a header and a body. Testing validates that these envelopes are properly formed and processed. The header often carries critical metadata such as authentication credentials, digital signatures, or transaction identifiers. The body contains the operation being invoked along with its parameters. SOAP API testing verifies that both sections are parsed correctly and that required elements are present and enforced.

From a functional perspective, SOAP API testing confirms that each defined operation behaves consistently for valid and invalid inputs. This includes validating response accuracy, fault handling, and edge cases. Because SOAP APIs are frequently used in enterprise workflows, testing also evaluates transactional behavior such as atomicity, rollback handling, and predictable fault responses when errors occur mid process.

Security testing is a core component of SOAP API testing. Many SOAP services rely on WS Security standards rather than simple transport level protections. Testing validates message level encryption, digital signatures, identity assertions, and replay protection. These controls are explicit and enforceable, but they also introduce complexity that must be tested thoroughly to avoid misconfiguration or partial enforcement.

SOAP API testing is typically performed in pre production environments using contract aware tools that generate compliant requests directly from the WSDL. This approach provides strong guarantees around consistency and standards compliance. However, it also introduces rigidity. Any change to the contract requires coordinated updates to clients, tests, and integrations, which can slow iteration compared to REST based services.

From a leadership perspective, SOAP API testing offers predictability and control at the cost of flexibility. It is well suited for regulated environments and stable integrations, but it demands disciplined change management and continuous validation to remain secure as systems evolve.

Architecture of SOAP

SOAP API testing begins with the WSDL. The WSDL defines the full contract of the SOAP API, including available operations, message formats, data types, and communication rules. Test tools and clients use this contract to construct valid SOAP requests and to validate responses. Unlike REST API testing, where endpoints and payloads may evolve informally, SOAP API testing assumes that the contract is authoritative and must be enforced.

At the message level, SOAP requests are wrapped inside an XML envelope. The envelope contains a header and a body. The header may include metadata such as authentication tokens, digital signatures, or transaction identifiers. The body contains the actual operation being invoked and its parameters. SOAP API testing validates that each part of this structure is present, correctly formatted, and processed as expected by the service.

From a functional perspective, SOAP API testing verifies that defined operations behave correctly for valid inputs and return predictable responses. This includes checking data integrity, schema validation, and error handling. Because SOAP APIs often support complex workflows, testing also validates transactional behavior, such as atomic operations, rollback handling, and fault responses.

Security testing is a core component of SOAP API testing. As outlined in the SOAP API testing research, SOAP commonly relies on WS Security standards rather than simple transport level controls. Tests validate message level encryption, digital signatures, identity assertions, and replay protection. This makes SOAP API testing more configuration heavy than REST API testing, but also more explicit in how security controls are enforced.

SOAP API testing is typically performed in pre production environments, using contract aware tools that can parse WSDL files and generate compliant requests. While this approach provides strong guarantees around correctness and standards compliance, it also introduces rigidity. Any change to the contract requires updates to test cases, tooling, and client integrations, which can slow iteration compared to REST APIs.

In the broader soap vs rest api comparison, SOAP API testing reflects the protocol’s design philosophy. It emphasizes strict validation, formal contracts, and predictable behavior. These qualities make SOAP reliable for legacy and regulated systems, but they also highlight why many organizations adopt REST APIs when flexibility, speed, and simpler testing models are required.

What is REST?

REST, or Representational State Transfer, is an architectural style for designing APIs that communicate over standard web protocols, most commonly HTTP. Unlike SOAP, which is built around a strict contract and messaging standard, REST APIs are resource oriented. They expose data and functionality as resources that can be accessed and manipulated using standard HTTP methods such as GET, POST, PUT, PATCH, and DELETE.

In practical terms, a REST API is designed to be simple, flexible, and scalable. Each API endpoint represents a specific resource, such as a user, order, or transaction, and interactions with that resource are stateless. This means every request contains all the information required to process it, without relying on server side session state. This design principle is one of the key reasons REST APIs dominate modern web, mobile, and cloud native applications.

From a business perspective, REST APIs enable faster development cycles, easier integrations, and broader ecosystem adoption. They align naturally with microservices, API first strategies, and distributed systems, which is why REST has become the default choice for most modern API platforms.

How does REST API Testing work?

REST API testing focuses on validating how APIs behave under real world usage rather than enforcing a rigid contract. Because REST APIs are resource oriented and evolve rapidly, testing is less about strict schema compliance and more about verifying correctness, access control, data exposure, and business logic across changing endpoints.

Instead of relying on a single authoritative definition like a WSDL, REST API testing evaluates how endpoints respond to different HTTP methods, parameters, and payloads. Tests validate that each endpoint returns the correct status codes, handles errors safely, and exposes only the data that the caller is authorized to access. This makes REST API testing inherently behavior driven rather than specification driven.

Security testing plays a central role in REST API testing. Since most REST APIs rely on token based authentication models, tests must confirm that authentication and authorization are enforced consistently across all resources. This includes validating object level access controls, preventing excessive data exposure, and detecting logic flaws where valid requests can be abused in unintended sequences or volumes.

Because REST APIs change frequently, effective testing must be continuous and automated. Pre production testing ensures new endpoints and logic changes do not introduce regressions, while runtime testing helps identify misuse patterns that only emerge under real traffic. Together, these approaches ensure REST APIs remain secure, reliable, and compliant as they scale.

In contrast to SOAP API testing, which prioritizes contract enforcement, REST API testing prioritizes resilience, adaptability, and real world risk reduction.

Architecture of REST 

REST API testing focuses on validating how API endpoints behave under real world usage rather than enforcing a rigid contract. While specifications such as OpenAPI provide structure, REST API testing assumes that behavior can evolve rapidly as applications change. This makes testing both more flexible and more complex compared to SOAP.

At the architectural level, REST API testing evaluates endpoints that are exposed via URLs and accessed using HTTP methods. Each test validates three core elements: the request, the response, and the state transition. The request includes the method, headers, parameters, and payload. The response is validated for status codes, headers, and data integrity. The state transition ensures that the API behaves correctly across sequences of requests, not just in isolation.

Unlike SOAP, REST APIs typically rely on lightweight data formats such as JSON. REST API testing validates schema consistency, field level authorization, and proper handling of optional and missing data. Because REST APIs often serve multiple client types, including web apps, mobile apps, and third party services, testing must account for a wide range of request patterns and edge cases.

Security testing is a critical component of REST API testing. REST APIs commonly use token based authentication models such as OAuth, JWT, or API keys. Testing validates that authentication is enforced consistently across endpoints and that authorization controls prevent access to unauthorized resources. This includes detecting issues such as broken object level authorization, excessive data exposure, and insecure direct object references, which are among the most common REST API vulnerabilities.

From an operational standpoint, REST API testing is most effective when automated and continuous. Because REST APIs evolve frequently, point in time testing quickly becomes outdated. Modern REST API testing integrates into pre production pipelines and staging environments, validating new endpoints, changes in business logic, and security controls before deployment.

In contrast to SOAP, REST API testing trades contractual rigidity for speed and adaptability. This flexibility enables rapid innovation, but it also increases the risk of security gaps if testing does not keep pace with change. For organizations operating at scale, effective REST API testing becomes essential to maintaining trust, reliability, and security as APIs grow and evolve.

SOAP vs REST: Differences 

While SOAP and REST APIs both enable system to system communication, they are designed around very different architectural philosophies. These differences have meaningful implications for scalability, flexibility, security controls, and how organizations manage risk as APIs evolve. Understanding the difference between SOAP and REST APIs helps enterprises choose the right model based on business criticality, regulatory requirements, and delivery velocity.

The table below outlines the key differences between SOAP vs REST APIs across architecture, testing, security, and operational impact.

Example of REST and SOAP API

Understanding the difference between SOAP and REST APIs becomes clearer when viewed through real world enterprise scenarios. While both enable data exchange, the way they expose functionality and enforce controls has meaningful implications for security, compliance, and operational resilience.

Example of a SOAP API

Scenario: Financial transaction processing in a regulated environment

Consider a core banking system that processes interbank fund transfers. This system exposes a SOAP API to partner institutions for initiating transfers, validating account balances, and confirming settlements.

In this example, the SOAP API is defined by a WSDL contract that strictly specifies available operations, required parameters, data types, and message structure. Each request is wrapped in an XML envelope that includes headers for authentication, digital signatures, and transaction identifiers. Security controls are enforced at the message level using WS Security standards, including encryption and signature validation.

From an operational perspective, this SOAP API prioritizes predictability and compliance. Only predefined operations can be invoked, and any deviation from the contract is rejected outright. Testing focuses heavily on schema validation, transaction integrity, and fault handling to ensure that financial operations remain atomic and auditable.

Security implication

The strict contract reduces ambiguity and limits unexpected behavior, but it also creates rigidity. Any change to the API requires coordinated updates across clients, tests, and governance processes. This makes SOAP APIs slower to evolve but easier to reason about from a compliance standpoint.

Example of a REST API

Scenario: Customer account management for a digital platform

Now consider a modern customer facing application that allows users to view account details, update personal information, and manage subscriptions. This functionality is exposed through a REST API consumed by mobile apps, web clients, and partner services.

In this case, REST endpoints represent resources such as /users, /accounts, or /subscriptions. Clients interact with these resources using standard HTTP methods like GET, POST, PUT, and DELETE. Payloads are typically JSON, and authentication is handled using token based mechanisms such as OAuth.

Unlike SOAP, the REST API does not rely on a single rigid contract. While an OpenAPI specification may exist, enforcement often depends on implementation discipline rather than protocol guarantees. Testing focuses on validating authentication, authorization, input handling, and business logic behavior across many possible request patterns.

Security implication

The flexibility of REST APIs enables rapid iteration and broad integration, but it also increases the attack surface. Authorization flaws, data overexposure, and logic abuse often emerge when endpoints evolve faster than security controls and testing processes.

Key Takeaway

SOAP APIs are designed for environments where predictability, standardization, and formal governance are paramount. REST APIs are designed for scale, speed, and composability, which makes them central to modern digital businesses but also harder to secure with static or periodic controls.

For organizations operating both models, the challenge is not choosing SOAP versus REST. It is ensuring that REST APIs receive the same level of rigor and continuous validation that SOAP APIs historically enforced through contracts, without sacrificing delivery velocity.

Types of vulnerabilities in REST vs SOAP API

While both SOAP and REST APIs enable critical business operations, the types of vulnerabilities they introduce differ significantly due to their underlying design philosophies, security models, and usage patterns. Understanding these differences is essential when assessing risk across modern API ecosystems.

Common Vulnerabilities in SOAP APIs

SOAP APIs are built around strict contracts and standardized messaging, which reduces ambiguity but introduces a different class of risks.

1.XML related attacks

Because SOAP relies heavily on XML, it is susceptible to XML specific attacks such as XML External Entity injection and XML schema poisoning. If XML parsing is not securely configured, attackers can exploit entity resolution to access internal files or trigger denial of service conditions.

2. WWS Security misconfigurations

SOAP APIs often depend on WS Security for message level encryption, digital signatures, and identity assertions. While powerful, this model is complex. Misconfigured signatures, weak encryption algorithms, or improper key management can allow attackers to tamper with messages or bypass authentication checks.

3. Replay and message tampering risks

SOAP APIs commonly support transactional workflows. If replay protection mechanisms such as timestamps or nonces are not enforced correctly, attackers may reuse valid messages to repeat sensitive operations like payments or account updates.

4. Operational blind spots

Because SOAP APIs are frequently treated as legacy or stable systems, they are often excluded from continuous testing. Over time, outdated libraries, unpatched parsers, or deprecated security policies can persist unnoticed, increasing long term exposure.

Scenario example

In a payment settlement system, an improperly validated SOAP message replay could result in duplicate fund transfers, even though authentication and encryption appear intact.

Common Vulnerabilities in REST APIs

REST APIs prioritize flexibility, scalability, and rapid iteration, which makes them foundational to modern digital platforms. That same flexibility also expands the attack surface.

1.Broken object level authorization and IDOR

One of the most prevalent REST API vulnerabilities occurs when authenticated users can access or modify objects they do not own by manipulating resource identifiers. This is a leading cause of data exposure incidents.

2. Excessive data exposure

REST endpoints often return more data than necessary, relying on clients to filter responses. Attackers can exploit this behavior to extract sensitive fields that were never intended to be exposed.

3. Authentication and token misuse

REST APIs commonly use token based authentication. Long lived tokens, overly broad scopes, or poor token validation enable token replay, privilege escalation, and lateral movement using legitimate credentials.

4. Business logic abuse

Unlike SOAP, REST APIs rarely enforce strict contracts for workflows. Attackers can chain valid requests in unintended sequences or volumes to exploit business logic, bypass rate limits, or manipulate system behavior.

5. Shadow and undocumented endpoints

Because REST APIs evolve quickly, undocumented or forgotten endpoints are common. These endpoints often lack consistent authentication, authorization, or monitoring, making them attractive targets.

Scenario example

In a subscription management API, an attacker may use a valid token to repeatedly invoke downgrade and refund endpoints in sequence, exploiting logic gaps rather than technical flaws.

REST vs SOAP API Vulnerability Landscape

From a security perspective, SOAP vulnerabilities tend to stem from complexity and configuration, while REST vulnerabilities more often arise from scale, speed, and inconsistency.

SOAP APIs fail when standards are implemented incorrectly or left unmaintained. REST APIs fail when rapid change outpaces visibility, testing, and governance.

This distinction is critical for security leaders. Legacy SOAP systems may appear safer due to rigidity, but they can hide deeply embedded risks. REST APIs may appear simple, but their distributed nature makes them harder to reason about without continuous security validation.

Advantages of REST API over SOAP

The shift from SOAP to REST across modern enterprises is not accidental. While SOAP APIs remain relevant in certain regulated and transactional environments, REST APIs have become the dominant choice for digital platforms, cloud services, and API first architectures. This preference is driven by a combination of business agility and security practicality.

1.Greater Agility and Faster Time to Market

REST APIs are easier to design, implement, and evolve than SOAP APIs. They rely on lightweight HTTP methods and flexible payloads, typically using JSON, which reduces development overhead.

Business value

Teams can iterate faster, release features more frequently, and integrate new partners or applications without complex contract renegotiations. This agility directly supports digital transformation and revenue growth.

Security tradeoff

Faster change increases risk if security does not keep pace. Without continuous discovery and testing, new endpoints or modified logic can introduce vulnerabilities unnoticed.

2. Simpler Integration Across Modern Ecosystems

REST APIs are platform agnostic and widely supported across web, mobile, cloud, and third party services. This makes them ideal for distributed architectures and external integrations.

Business value

Organizations can scale ecosystems around partners, developers, and customers with minimal friction, enabling API driven business models and monetization strategies.

Security tradeoff

Wider exposure increases the attack surface. REST APIs must be secured consistently across internal, external, and partner facing endpoints to prevent unauthorized access and data leakage.

3. Stateless Design and Improved Scalability

REST APIs are stateless by design. Each request contains all the information needed to process it, which simplifies scaling and load balancing.

Business value

Statelessness supports high availability, global distribution, and cost efficient scaling, which is essential for modern SaaS and cloud platforms.

Security tradeoff

Because trust is evaluated per request, authentication and authorization must be enforced rigorously. Weak token handling or inconsistent authorization checks can lead to replay attacks and privilege abuse.

4. Lower Operational and Maintenance Overhead

SOAP APIs require strict WSDL contracts, XML schemas, and WS Security configurations. REST APIs avoid much of this complexity.

Business value

Lower operational overhead reduces long term maintenance costs and dependency on specialized skill sets. This makes REST APIs easier to sustain as teams and technologies evolve.

Security tradeoff

The lack of rigid contracts shifts responsibility to governance and testing. Without automated validation, REST APIs can drift from intended behavior over time.

5. Better Alignment with Modern Security Models

REST APIs integrate naturally with modern security patterns such as OAuth, OpenID Connect, and zero trust architectures.

Business value

Security becomes more adaptable and interoperable across identity providers, cloud services, and external platforms.

Security tradeoff

Token based models introduce new risks if scopes, lifetimes, and validation are poorly designed. Authentication alone is insufficient without robust authorization and logic testing.

Why REST Has Become the Default Choice

The advantages of REST API over SOAP extend beyond simplicity. REST aligns more closely with how modern businesses build, scale, and expose digital services.

However, this advantage comes with responsibility. REST APIs shift security from rigid standards enforcement to continuous control. Visibility, testing, and governance become essential to prevent flexibility from turning into risk.

Benefits of REST and SOAP APIs 

REST and SOAP APIs each deliver distinct benefits, and many enterprises continue to operate both in parallel. The value of each approach becomes clearer when viewed through real world usage scenarios rather than purely technical comparisons.

Benefits of REST APIs

REST APIs excel in environments where speed, scale, and ecosystem integration matter most.

Scenario: Digital customer platforms

A retail or fintech organization exposing APIs to mobile apps, partner platforms, and third party developers benefits from REST’s lightweight design. REST APIs allow teams to roll out new endpoints quickly, scale traffic during peak demand, and onboard partners without heavy integration overhead.

Business benefit

REST APIs accelerate innovation and time to market. Teams can experiment, iterate, and expand API driven services without being slowed down by rigid contracts or complex tooling.

Security benefit

REST APIs align well with modern identity models such as OAuth and token based access. When implemented correctly, this supports granular access control and zero trust architectures. The tradeoff is that security must be continuously validated as APIs evolve, since flexibility can introduce drift if left unchecked.

Benefits of SOAP APIs

SOAP APIs remain valuable in environments where predictability, transactional integrity, and formal standards are required.

Scenario: Financial and regulated transactions

In banking, insurance, or enterprise resource planning systems, SOAP APIs are often used for payment processing, claims handling, or order fulfillment. These workflows require strict schemas, guaranteed message delivery, and well defined error handling.

Business benefit

SOAP APIs provide stability and contractual certainty. Changes are deliberate, controlled, and auditable, which reduces unexpected downstream impact in complex enterprise systems.

Security benefit

SOAP APIs benefit from built in standards such as WS Security, which support message level encryption, signatures, and integrity checks. This makes security controls explicit and enforceable, though often at the cost of agility and operational complexity.

Why Many Enterprises Use Both

Most organizations do not choose between REST and SOAP in isolation. Instead, they adopt a hybrid approach.

Scenario: Legacy modernization

An enterprise modernizing customer-facing services may adopt REST APIs for mobile and web applications while continuing to rely on SOAP APIs for backend systems of record. This allows innovation at the edge while preserving stability at the core.

Business benefit

This approach balances speed and reliability, enabling modernization without disrupting mission critical workflows.

Security benefit

Hybrid environments demand consistent visibility and testing across both API types. Security gaps often emerge not because REST or SOAP is inherently insecure, but because controls differ across teams, tools, and generations of technology.

From a security leadership standpoint, the benefits of REST and SOAP APIs are realized only when their risks are understood and governed appropriately. REST enables growth and flexibility. SOAP enforces rigor and control. Both require security strategies that match how APIs are actually built, deployed, and used.

When to use which: REST vs SOAP API

Choosing between REST and SOAP is rarely a purely technical decision. It is a tradeoff between agility, control, and risk tolerance, shaped by regulatory demands, integration complexity, and how fast the business needs to move. Understanding when each model fits best helps security and engineering leaders align architecture with long term objectives.

When SOAP Is the Right Choice

SOAP APIs are best suited for environments where strict contracts, formal governance, and compliance guarantees are non-negotiable.

In highly regulated industries such as banking, insurance, and government services, SOAP remains relevant because of its strong emphasis on standards. SOAP APIs rely on WSDL contracts that explicitly define operations, data structures, and error handling. This predictability reduces ambiguity and makes it easier to demonstrate compliance during audits.

From a security perspective, SOAP’s native support for WS Security enables message level encryption, digital signatures, and identity assertions independent of transport. This is valuable when APIs traverse multiple intermediaries or when end to end message integrity must be proven.

A practical example is a financial institution integrating with legacy core banking systems or clearing networks. These systems prioritize transactional integrity, non repudiation, and deterministic behavior over speed of iteration. In such cases, SOAP provides confidence that every interaction conforms to a predefined and enforceable contract.

SOAP is also appropriate when integrations are long lived and slow to change. If an API is expected to remain stable for years and changes require formal coordination across multiple parties, SOAP’s rigidity becomes an advantage rather than a drawback.

When REST Is the Better Fit

REST APIs are designed for speed, flexibility, and scale, which makes them the dominant choice for modern digital platforms.

REST aligns naturally with cloud native architectures, microservices, and mobile applications. Its resource based model, lightweight JSON payloads, and stateless communication enable rapid development and frequent releases. This makes REST ideal for customer facing APIs, partner integrations, and internal services that evolve continuously.

From a business standpoint, REST enables faster product experimentation and integration with third party ecosystems. New endpoints can be introduced without redefining a rigid contract, allowing teams to respond quickly to market demands.

Security in REST relies heavily on OAuth, OpenID Connect, and transport layer protections. While this shifts responsibility away from message level controls, it simplifies implementation and supports horizontal scaling. REST is particularly effective when paired with continuous security testing and runtime monitoring, which compensate for its looser structure.

A common example is an ecommerce platform exposing APIs to mobile apps and external partners. These APIs must scale globally, handle burst traffic, and change frequently. REST provides the flexibility needed to support such growth without introducing excessive operational overhead.

The Modern Reality: Mixed Environments

Most enterprises today do not choose exclusively between REST and SOAP. Instead, they operate hybrid environments.

Legacy SOAP APIs often continue to power mission critical backend systems, while REST APIs dominate new customer facing and partner driven initiatives. This coexistence introduces complexity, especially around security and governance. Different testing approaches, authentication models, and visibility gaps emerge across protocols.

From a leadership perspective, the key question is not SOAP vs REST in isolation, but whether the organization can secure both consistently as APIs evolve. This is where continuous discovery, testing, and monitoring become essential, regardless of protocol.

Challenges of using REST and SOAP API and its solutions 

REST and SOAP APIs each bring distinct advantages, but they also introduce different operational and security challenges. For security and technology leaders, the issue is rarely choosing a perfect model. It is understanding where each approach creates friction and how those gaps are addressed without slowing delivery or increasing risk.

Challenges Common to SOAP APIs

One of the primary challenges with SOAP APIs is operational rigidity. SOAP relies on strict WSDL contracts that define how services must behave. While this improves predictability, it also makes change management slow. Even small updates often require coordinated changes across clients, test suites, and integration partners.

From a business perspective, this rigidity can delay modernization initiatives. Teams may hesitate to improve or extend APIs because of the downstream impact, which increases the likelihood that legacy interfaces remain exposed longer than intended.

Another challenge is complexity of configuration and maintenance. SOAP security standards such as WS Security are powerful, but they require careful configuration and ongoing management. Misconfigurations in message level encryption, signatures, or identity assertions can lead to gaps that are difficult to detect without specialized testing.

Performance is also a consideration. XML based payloads and verbose message structures increase processing overhead. At scale, this can affect latency and infrastructure costs, especially when SOAP services are used beyond their original transactional scope.

How organizations address this

Enterprises typically mitigate SOAP challenges by limiting SOAP usage to well defined, stable domains such as core transactions. They invest in contract aware testing and strict change governance, and increasingly place SOAP services behind modern API management layers to improve visibility, monitoring, and access control.

Challenges Common to REST APIs

REST APIs face a different set of challenges driven by their flexibility and speed. Because REST does not enforce strict contracts in the same way as SOAP, inconsistencies in endpoint behavior, payload structure, and authorization logic can emerge as APIs evolve rapidly.

From a security standpoint, REST APIs are especially vulnerable to logic flaws. Many high impact incidents occur when valid, authenticated requests are used in unintended ways. Issues such as broken object level authorization, excessive data exposure, and abuse of business workflows are common in REST based systems.

Another challenge is API sprawl. REST APIs are easy to create and deploy, which often leads to undocumented, deprecated, or shadow endpoints accumulating over time. These endpoints may bypass standard security reviews and become prime targets for attackers.

REST also places significant reliance on transport level security and token based authentication. While effective when implemented correctly, inconsistent enforcement or misconfigured scopes can expose sensitive data without obvious failures.

How organizations address this

To manage REST risks, mature teams focus on continuous discovery, automated security testing, and runtime monitoring. Rather than relying solely on design time reviews, they validate how APIs behave with real data and realistic usage patterns across environments.

Shared Challenges Across Both Models

Regardless of protocol, both REST and SOAP APIs struggle with visibility and assurance at scale. As the number of APIs grows, it becomes difficult to answer basic questions about what exists, who uses it, and how securely it is operating.

Manual testing and periodic assessments cannot keep pace with continuous delivery. This creates gaps between development intent and production reality, where vulnerabilities persist unnoticed.

How organizations address this

Leading organizations shift toward continuous, automated approaches that span pre production and production environments. By combining discovery, documentation, security testing, and monitoring, they move from reactive fixes to proactive control.

Best Practices to follow for REST and SOAP API Testing

Effective API testing is less about the protocol itself and more about how consistently security, correctness, and behavior are validated as APIs evolve. For REST and SOAP APIs, best practices differ in execution but align on a shared goal: reducing risk early while maintaining delivery speed.

1.Start With Complete API Visibility

Before testing can be effective, teams must know what exists. This applies equally to REST and SOAP APIs.

Best practice

Maintain a continuously updated inventory of all APIs and endpoints across development, staging, and production, including internal, external, partner, deprecated, and shadow APIs.

Why it matters

Untested APIs are indistinguishable from insecure APIs. Visibility gaps are a common root cause of breaches in both REST and SOAP environments.

2. Test APIs Before and After Deployment

API testing should not be confined to a single phase of the lifecycle.

For SOAP APIs

Focus heavily on pre production, contract driven testing. Validate WSDL compliance, schema correctness, and strict adherence to defined operations before deployment.

For REST APIs

Combine pre production testing with ongoing validation. REST APIs change frequently, and testing must keep pace with new endpoints, parameters, and logic paths.

Why it matters

Point in time testing misses drift. Continuous testing ensures that changes introduced after release do not quietly introduce risk.

3. Validate Authentication and Authorization Explicitly

Authentication alone is not sufficient for either REST or SOAP APIs.

For SOAP APIs

Test WS Security controls thoroughly, including message signatures, encryption, identity assertions, and replay protection. Validate that security headers are required and correctly enforced for every operation.

For REST APIs

Test token handling, scope enforcement, and object level authorization. Validate that authenticated users and services can only access resources they are explicitly permitted to.

Why it matters

Many API breaches involve valid credentials used improperly. Testing must confirm not just who can call an API, but what they can do once authenticated.

4. Go Beyond Schema and Input Validation

Traditional API testing often focuses on structure. Modern risks lie in behavior.

Best practice

Test business logic, request sequencing, and abuse scenarios. Simulate realistic usage patterns, role changes, and repeated actions that could expose logic flaws.

Why it matters

The most damaging API attacks often involve legitimate requests executed in unintended ways, especially in REST APIs with complex workflows.

5. Use Realistic Data and Context Aware Testing

Tests should reflect how APIs are actually used, not just how they are designed.

Best practice

Use representative data, real authentication flows, and production-like configurations during testing.

Why it matters

Synthetic or overly simplified tests fail to uncover issues that only appear under real world conditions.

6. Automate Wherever Possible

Manual testing does not scale with modern API ecosystems.

Best practice

Automate REST and SOAP API testing within CI pipelines and scheduled workflows. Ensure tests run consistently without manual intervention.

Why it matters

Automation ensures coverage keeps pace with delivery and reduces reliance on periodic assessments that leave long exposure windows.

7. Monitor and Revalidate in Production

Testing does not end at deployment.

Best practice

Continuously monitor API behavior in production and revalidate assumptions made during testing.

Why it matters

Integration patterns, usage volumes, and client behavior often change after release. Continuous validation helps detect misuse and drift early.

8. Treat REST and SOAP Differently, Govern Them Together

While REST and SOAP require different testing techniques, governance should be unified.

Best practice

Apply consistent policies for visibility, testing frequency, risk classification, and reporting across both REST and SOAP APIs.

Why it matters

Security leadership needs a unified view of risk, regardless of protocol or architecture.

How Levo facilitate API Management in transition from SOAP to REST

Modern digital transformation often involves evolving legacy service architectures toward more flexible, scalable, and developer friendly interfaces. For many enterprises, this means transitioning from SOAP APIs to REST APIs. While REST offers agility and broad ecosystem integration, the transition is rarely straightforward. Legacy systems, compliance requirements, and dependent clients often mean SOAP cannot be retired overnight. Security leaders need an approach that supports coexistence, minimizes risk during migration, and ensures consistent governance across both protocols.

Levo is designed to support this journey by providing unified visibility, continuous discovery, and risk-aware testing across SOAP and REST APIs, enabling organizations to manage transformation without sacrificing security.

1.Continuous API Discovery Across Protocols

A recurring challenge during migration is incomplete visibility. Legacy SOAP APIs may be poorly documented, and newly introduced REST APIs may proliferate through microservices or partner projects. Levo continuously discovers all API endpoints across environments, including internal, external, third party, shadow, and deprecated interfaces, regardless of protocol. This ensures security teams always have an accurate inventory as services evolve from SOAP to REST without relying on manual registration.

By bringing both SOAP and REST APIs into a single catalog, Levo reduces blind spots and enables consistent assessment of how each API is used, what data it handles, and how it should be governed.

2. Unified Documentation and Change Tracking

Migrating from SOAP to REST often uncovers gaps between design time intent and runtime behavior. Levo automatically generates API documentation from real traffic patterns and runtime metadata. This includes operational details such as supported methods, schemas, error responses, and authentication requirements.

This real world documentation helps remove assumptions that are common during migration, such as outdated WSDL files for SOAP or incomplete OpenAPI specs for REST. It also makes it easier to ensure that REST APIs introduced as part of migration meet the same transparency standards that SOAP contracts historically provided.

2. Continuous and Context Aware Security Testing

Security testing is a core component of safely transitioning from SOAP to REST. Traditional SOAP API testing focuses on contract compliance, but REST API testing must validate behavior, business logic, and access control across a broader range of scenarios.

Levo’s automated testing platform supports both SOAP and REST models:

• For SOAP APIs, tests validate strict contract adherence, message structure, WS Security controls, and transactional integrity.
• For REST APIs, tests go beyond schema validation to simulate real world usage, detect broken object level authorization, excessive data exposure, and business logic abuse.

By applying consistent testing across both API types, Levo ensures that transformation efforts do not create new security gaps. Endpoints are tested continuously as they are updated, not merely at a single point in time.

3. Real Time Monitoring and Runtime Protection

As REST services are introduced alongside legacy SOAP systems, runtime visibility becomes essential. REST APIs, by design, evolve faster and are consumed more broadly, increasing the need for live monitoring and anomaly detection.

Levo’s monitoring capabilities provide continuous awareness of how both SOAP and REST APIs are actually used in production. This includes authentication patterns, unusual access sequences, and deviations from expected usage. Real time monitoring helps detect misconfigurations, logic abuse, or unexpected exposure of sensitive data that may not be apparent through pre production tests alone.

4. Single Control Plane for Dual Protocol Governance

One of the core strengths Levo brings to the SOAP to REST transition is a unified control plane. Security, testing, monitoring, and governance controls are consistent across SOAP and REST APIs. This reduces operational friction that often arises when different tools or processes are used for each style.

For security leaders, this unified approach enables:

• Consistent application of policies and standards regardless of API protocol
• Centralized risk reporting and audit readiness
• Continuous compliance evidence across hybrid environments
• Faster identification and remediation of vulnerabilities across both legacy and modern APIs

5. Supporting Safe Modernization Without Operational Disruption

Migrating from SOAP to REST is seldom linear. Organizations often face overlapping lifecycles, dual support requirements, and dependencies that must remain operational throughout transformation. Levo supports these complex transitions by enabling security teams to validate every change continuously, not retrospectively. This reduces the risk that modernization introduces new vulnerabilities or compliance gaps.

By combining discovery, documentation, testing, monitoring, and governance into a cohesive platform for both SOAP and REST APIs, Levo helps enterprises realize the business benefits of API modernization without compromising security posture or delivery velocity.

Achieve Complete API Security for REST and SOAP APIs with Levo

Securing both REST and SOAP APIs requires a unified approach that spans discovery, testing, monitoring, and runtime protection. REST’s flexibility and SOAP’s strict contracts create distinct security requirements, but modern API ecosystems cannot manage these in isolation. Levo’s API security platform brings together comprehensive capabilities so organizations can protect every endpoint, regardless of protocol or pace of change.

Levo helps enterprises achieve complete API security across both REST and SOAP environments by addressing visibility gaps, testing limitations, runtime risk, and compliance needs.

1.Continuous API Discovery and Inventory

Before security can be enforced, you must know what APIs exist and how they behave.

Levo automatically discovers all REST and SOAP APIs across environments, including internal, external, partner, and undocumented endpoints. This reduces the risk of shadow and zombie APIs slipping into production untested and ungoverned.

With an up-to-date API inventory, security teams can confidently answer questions such as:

• What APIs are currently running?
• Which protocols do they use?
• Who owns them?
• How frequently are they modified?

This continuous discovery lays the foundation for complete API security by eliminating blind spots that attackers exploit.

2. Accurate, Runtime Driven Documentation

Documentation is more than a developer convenience. It is a security asset.

Levo generates documentation directly from runtime behavior, capturing real usage patterns, authentication details, input parameters, and error responses for both REST and SOAP APIs. Unlike manually maintained specs that quickly become outdated, Levo’s documentation reflects how APIs actually work in production.

Accurate documentation enables:

• Better security testing coverage
• Clearer compliance evidence
• Faster onboarding of security controls
• Reduced assumptions about API behavior

3. Automated and Context-Aware Security Testing

Testing remains one of the most effective ways to reduce risk—when done thoroughly and continuously.

Levo’s testing capabilities extend beyond basi input validation:

For REST APIs, Levo tests for logic flaws such as broken object level authorization, data overexposure, and abuse paths that emerge only under real world usage.

For SOAP APIs, Levo validates contracts, message structures, WS Security enforcement, and transactional integrity.

Testing is automated and tailored to each API’s schema and authentication model. This enables continuous validation across CI/CD pipelines and reduces gaps lft by manual or periodic testing.

4. Sensitive Data Discovery and Risk Classification

APIs frequently handle the most sensitive assets in an organization—personally identifiable information, health data, payment details, and business critical records.

Levo automatically detects where sensitive data appears in API traffic and maps it back to specific endpoints and fields. This enables risk prioritized testing and governance so that high impact APIs receive deeper scrutiny.

For security teams, this means proactive risk reduction rather than reactive firefighting after data leaks occur.

6. Runtime Monitoring and Behavioral Detection

Security does not end when testing stops. APIs in production continue to evolve, and adversaries constantly probe for new weaknesses.

Levo provides continuous runtime monitoring for both REST and SOAP endpoints. It tracks how APIs are used, detects anomalous behaviors, and correlates activity across services. For environments using MCP servers or agent based interactions, Levo maps these flows to ensure visibility into non human actors and automated processes.

This layer helps detect:

• Misuse of valid tokens
• Deviations from expected access patterns
• Logic abuse in workflows
• Credential compromise attempts

7. Unified Vulnerability Reporting and Governance

Finding issues is only half the battle. Teams need clarity and prioritization.

Levo consolidates findings from both REST and SOAP testing into unified reporting dashboards. Each finding is linked to the impacted API, endpoint, security control, and owner. Reports can be tailored for compliance reviews, leadership dashboards, or technical remediation planning.

This enables:

• Consistent risk scoring
• Clear ownership and tracking

Audit ready evidence for frameworks such as PCI, SOC 2, GDPR, and industry specific standards

9. Inline Protection and Enforcement

Beyond detection and testing, Levo enables proactive enforcement of security policies at runtime. This means suspicious activity can be blocked or flagged before it impacts systems or data.

Inline protection works with authentication and authorization models to enforce:

• Rate limits
• Access policies
• Role based controls
• Business intent validations

This layer ensures that APIs do not just pass tests in isolation but stay protected as traffic evolves and threat patterns shift.

Conclusion

Transitioning from SOAP to REST and securing APIs at scale demands more than isolated tools. It requires continuous control, contextual understanding, and runtime awareness. Levo integrates discovery, documentation, testing, monitoring, and protection into a coherent platform so organizations can:

• Maintain consistent security posture across hybrid API ecosystems
• Reduce blind spots and unknown endpoints
• Identify and remediate flaws before they reach production
• Prove compliance continuously rather than periodically
• Enable accelerated innovation with confidence

In today’s landscape, where APIs power business differentiators and attackers target the weakest link, achieving complete API security with Levo means closing gaps across protocols, pipelines, and runtime behaviors while supporting both REST and SOAP API security with equal rigor and visibility.