Inconsistent or Incorrect Responses
An endpoint that returns the right data for one request type can return malformed or incomplete responses for edge cases, optional parameters or unexpected input combinations that manual spot-checks rarely cover.
API Testing
API Testing Services
Your front end is only as reliable as the APIs feeding it. We test every endpoint for correct responses, error handling, authentication and performance across REST, GraphQL and SOAP, catching status code errors, schema mismatches and edge cases before they ever reach a client.
- REST, GraphQL & SOAP
- Automated Test Suites
- Auth & Data Validation
- CI/CD Integration
0+ Years of combined experience
0+ API test suites delivered
0% Endpoint defects caught early
0/7 Monitoring & support
Common API Risks
What Happens When API Testing Gets Skipped
APIs fail quietly. A broken endpoint does not always throw an obvious error; it returns the wrong field or status code, and the damage shows up several layers downstream.
Authentication and Authorization Gaps
Endpoints that forget to verify a token, check a scope or enforce role-based permissions let users access or modify data they should never reach, often without throwing any visible error.
Breaking Changes Between Versions
A field renamed, a response structure altered or a parameter made required without warning breaks every client consuming that endpoint, frequently discovered only after integration partners report failures.
Poor Performance Under Concurrent Requests
An endpoint that responds instantly to a single test call can time out or throttle unpredictably once dozens of clients hit it simultaneously, an issue invisible until real traffic arrives.
Inadequate Error Handling
APIs that return generic 500 errors or expose internal stack traces instead of meaningful, structured responses make debugging difficult for consumers and can leak sensitive implementation details.
No Contract Validation Across Teams
Without a tested API contract, front-end and back-end teams drift apart on expected request and response formats, producing integration failures that surface late and are expensive to trace.
Our API Testing Stack
Tools Built for Verifying Every Endpoint
We select tools based on your API architecture and protocol, whether REST, GraphQL, SOAP or event-driven, so coverage matches how your services communicate.
Po Postman
So SoapUI
RA REST Assured
Sw Swagger / OpenAPI
In Insomnia
Ka Karate DSL
Ne Newman
JM JMeter
k6 k6
GQ GraphQL Playground
Pa Pact
Hc Apache HttpClient
Cy Cypress
cU cURL
Wm WireMock
Mo Mockoon
Ap Apigee
AW AWS API Gateway
Ch Charles Proxy
JS JSON Schema Validator
What We Test
API Testing Services We Offer
Every engagement is scoped around your actual API surface and how your services and clients depend on it, not a generic endpoint checklist.
Functional API Testing
Verifying every endpoint returns correct data, status codes and headers for valid requests, edge cases and invalid input.
Authentication & Authorization Testing
Confirming tokens, API keys, OAuth flows and role-based permissions are enforced correctly across every protected endpoint.
Schema & Contract Validation
Validating request and response payloads against defined schemas so front-end and back-end teams stay in sync as the API evolves.
Regression & Version Compatibility Testing
Catching breaking changes between API versions before they reach client applications or integration partners.
Load & Performance Testing
Measuring endpoint response times and throughput under concurrent requests to catch degradation before it affects real users.
Test Automation & CI/CD Integration
Building automated API test suites that run on every build, catching regressions the moment they are introduced.
Negative & Edge Case Testing
Testing malformed input, missing parameters, boundary values and unexpected request sequences that manual testing typically skips.
Third-Party & Integration Testing
Verifying your API behaves correctly against real third-party services and that integrations degrade gracefully on failure.
GraphQL Query & Mutation Testing
Testing GraphQL queries, mutations and subscriptions for correct resolution, authorization and performance under complex nested queries.
Mock & Stub Service Testing
Building mock services to test client applications against realistic API behavior before the real backend is ready.
API Documentation Validation
Confirming your OpenAPI or Swagger documentation matches actual endpoint behavior, so consumers integrate against accurate specs.
Ongoing API Monitoring
Continuous testing integrated into your release cycle so endpoint regressions are caught before they reach production.
Industries We Support
API Testing Across Integration-Heavy Sectors
API reliability requirements differ sharply depending on who consumes your endpoints and what is at stake when they fail.
SaaS Platforms
Financial Services
eCommerce & Retail
Healthcare
Travel & Hospitality
Logistics & Supply Chain
Online Marketplaces
Hotels & Booking Platforms
Startups & Scale-ups
Professional Services
Why Teams Choose Us
API Testing That Catches What Manual Checks Miss
Running a few requests through Postman tells you an endpoint works for the happy path. We test what happens everywhere else, so your contracts hold under real conditions.
Book a Free API Test Review-
Full Protocol Coverage
We test REST, GraphQL and SOAP APIs with the same rigor, adapting our approach to each protocol's specific failure modes.
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Deep Edge Case Testing
We deliberately test malformed input, missing fields and unexpected sequences, not just the requests your own team expects to send.
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Authorization Tested at Every Layer
Every endpoint is checked for proper access control, not just the ones that look security-sensitive on the surface.
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Automation Built to Last
Test suites are built for maintainability, so they keep providing value as your API evolves instead of breaking with every release.
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Contract-First Validation
We validate against your actual API schema, catching drift between documentation and real behavior before it confuses integration partners.
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CI/CD Native
Our API test suites run inside your existing pipeline, giving your team immediate feedback on every pull request and deployment.
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Performance Tested, Not Assumed
We measure real response times and throughput under load instead of assuming an endpoint that works alone will hold up in production.
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Support as Your API Grows
We extend test coverage as you add endpoints and versions, so your test suite scales alongside your actual API surface.
How We Work
Our API Testing Process
Every engagement follows a structured process designed to validate functionality, security and performance across your API surface.
- 01
API Discovery & Scoping
We review your documentation, endpoints and consumer integrations to define the scope and priority of testing.
- 02
Test Strategy & Schema Mapping
Request and response schemas are mapped against documentation to define expected behavior before any test is written.
- 03
Test Case & Script Design
Functional, negative and edge case scenarios are designed to cover real usage patterns, not just the documented happy path.
- 04
Functional & Contract Testing
Endpoints are tested against defined schemas, status codes and business logic to confirm contracts hold under every scenario.
- 05
Security & Authorization Testing
Authentication flows and access controls are verified across every protected endpoint to confirm permissions are enforced correctly.
- 06
Performance & Load Testing
Endpoints are tested under concurrent load to measure response times and identify throughput limits before they affect production.
- 07
Automation & CI/CD Integration
Test suites are automated and wired into your deployment pipeline so future regressions are caught automatically.
- 08
Reporting & Ongoing Maintenance
Findings are documented with clear fixes, and test suites are maintained as your API evolves with new endpoints and versions.
What Is Included
Ad-Hoc Checks Are Not the Same Asset
The difference between a one-off endpoint check and a professional test suite is everything that happens under the surface. Here is what comes standard with every engagement we deliver.
What you get Ad-hoc / Minimal Testing Devlon StedyDesk
Full schema and contract validation
Negative and edge case coverage
Authentication and authorization testing
Load testing under concurrent requests
Automated regression suite
CI/CD pipeline integration
GraphQL and SOAP protocol coverage
Basic happy-path request checks
Manual, one-off endpoint checks
Ongoing test suite maintenance
Client Words
Trusted by Teams That Depend on Their APIs
We had a public API used by over forty integration partners and no automated regression suite covering it. A version update broke a field type on one endpoint and three partners reported failures before we caught it ourselves. The automated suite they built now catches that class of issue on every build.
Our GraphQL API looked solid in every manual test until they ran nested query testing and found a performance issue that only appeared with deeply nested requests our larger clients were actually sending. That single fix resolved a recurring support complaint we had been chasing for months.
Authorization testing on our REST API found an endpoint where a regular user could access another account's transaction history by changing an ID in the request. It was fixed within a day, and re-testing confirmed it was closed before our next compliance review.
Questions, Answered
API Testing FAQs
How much does API testing cost?
Most engagements range from $2,500 to $22,000 depending on the number of endpoints, the protocols involved and whether automation and CI/CD integration are included. A focused test suite for a small set of REST endpoints sits at the lower end; full coverage across REST, GraphQL and SOAP with automated regression sits higher. Every quote is itemized after an initial scoping call.
How long does an API testing engagement take?
A focused test suite covering a limited set of endpoints typically takes 1 to 3 weeks. Full API coverage including automation, security and performance testing usually runs 4 to 8 weeks, with working test cases delivered throughout.
Do you perform regression testing on our API?
Yes. We build automated regression suites that re-run on every release, so changes to one endpoint do not silently break behavior that other endpoints or client applications depend on.
Can API testing be automated?
Yes. Automated test suites are central to how we approach API testing, since manual checks alone cannot keep pace with frequent releases or large numbers of endpoints.
Can API tests run inside our CI/CD pipeline?
Yes. We integrate automated API test suites directly into your deployment pipeline, so failing tests block problematic releases instead of reaching production.
How do you report bugs found during API testing?
Every issue is logged with the specific request that triggered it, the expected versus actual response, severity and reproduction steps, so your developers can fix it without needing to recreate the scenario themselves.
Does API testing cover security as well as functionality?
Yes. Authentication, authorization and input validation are tested as part of our standard API testing scope, alongside functional and performance checks, though a dedicated penetration test goes further for high-risk applications.
Do you test compatibility across different API versions?
Yes. We test for breaking changes between versions and confirm backward compatibility where required, so updates do not silently disrupt existing client integrations.
Can you test how our API performs at scale?
Yes. We test endpoints under concurrent load to measure throughput and response time degradation, giving you data on where performance limits sit before real traffic finds them.
Do you provide ongoing API testing, not just a one-time engagement?
Yes. Our maintenance plans extend test coverage as you add new endpoints and versions, keeping your automated suite aligned with your actual API surface over time.
What does the final API testing report include?
You receive a report covering every tested endpoint, defects found with severity and reproduction steps, schema validation results and performance metrics, along with a business-readable summary of overall API health.
What support is available after the engagement ends?
We offer ongoing test suite maintenance, scheduled re-testing after major changes and a support channel for questions as your API evolves. Most clients move to a recurring testing plan tied to their release cycle rather than a one-time engagement.
Keep Exploring
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ExploreSecurity Testing
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Automated test suites that catch regressions faster than manual QA cycles ever could.
ExploreMake Sure Every Endpoint Holds Up Before Your Clients Find Out Otherwise
Every API has a breaking point, an edge case nobody anticipated, a version change nobody flagged. Thorough API testing gives you a documented, repeatable way to catch those failures before a client integration does it for you.