API TestingTest the layer everything else depends on.
Automated testing of REST and GraphQL APIs for function, contracts, security, performance and integrations, running in your CI pipeline on every change.
- REST and GraphQL
- Contract testing
- In your CI
- QA Assessment1–2 weeks · Fixed price
- API Test Automation2–6 weeks · Fixed price
What is API testing?
API testing checks application programming interfaces directly, without a user interface: whether endpoints return the right data and status codes, handle invalid input, enforce authentication and permissions, meet performance targets and keep their contracts with consumers. Stack18 builds automated API test suites with tools such as Postman, REST Assured, Playwright or Karate, adds contract and security tests and runs them in your CI pipeline.
- REST API testing
- Postman automation
- contract testing
- API automation testing
- API QA services
Last reviewed 11 November 2026 by the Stack18 delivery team in Jaipur.Security & AI governancePricing
| What it covers | Functional tests; Contract tests; Security tests; Performance tests; Integration tests; CI automation. |
|---|---|
| Typical first step | QA Assessment: 1–2 weeks; fixed price. |
| Main engagement | API Test Automation: 2–6 weeks; fixed price. |
| Measured by | API test coverage; Defects caught before release; Breaking changes caught; Test run time. Each against an agreed baseline. |
| Governance | Human approval at 5 governance gates before anything reaches production. NDA available on request. |
| Delivery team | Based in Jaipur, India. A senior specialist replies within one business day. |
You need this when…
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API Testing, end to end.
The features and building blocks of an API Testing engagement. Each is delivered by the same team on the Agentic SDLC, with your approval at every critical step.
Functional tests
Endpoints checked for correct behaviour.
- Positive and negative cases
- Data validation
- Error handling
Contract tests
Producers and consumers kept in agreement.
- OpenAPI validation
- Consumer-driven contracts
- Breaking change alerts
Security tests
Authentication, authorisation and input attacks.
- Broken access control
- Injection tests
- Rate limit checks
Performance tests
Response times under load.
- Latency checks
- Load tests
- Throughput
Integration tests
End-to-end flows across services.
- Multi-service flows
- Third-party mocks
- Test data
CI automation
Tests on every change.
- Pipeline integration
- Reports
- Failure alerts
A typical engagement, step by step.
Senior people lead every phase. Specialised AI agents on the Agentic SDLC handle the repetitive work, and nothing ships without your approval.
Scope
We agree the scope, the systems or teams involved and how API test coverage and defects caught before release will be measured, so findings can be compared later.
Assess
We work through functional tests, contract tests and security tests, using your own data, systems and people rather than generic checklists.
Report
You get clear findings ranked by impact and effort, with practical recommendations your team can act on.
Fix and verify
We help fix the priority items if you want us to, then re-check API test coverage and defects caught before release to confirm the improvement.
How much does API Testing cost in India?
Most API Testing projects start with a QA Assessment (1–2 weeks, fixed price), which fixes the scope, team and price before you commit. API Test Automation takes 2–6 weeks at a fixed price. Prices exclude GST. Cloud hosting and third-party usage, such as messaging, payment or AI model charges, are paid at cost.
QA Assessment
Teams unsure where quality breaks down.
- Duration
- 1–2 weeks
- Pricing
- Fixed price
- Process review
- Risk-based test plan
- Tool recommendations
API Test Automation
Teams with growing APIs and services.
- Duration
- 2–6 weeks
- Pricing
- Fixed price
- Automated suite
- CI integration
- Coverage report
What drives the price
- Number of modules, workflows and user roles
- Integrations with your ERP, CRM, payments, GST or messaging tools
- Volume and quality of data to migrate
- Compliance, security and audit requirements
- Mobile apps, offline use or multiple languages
Always included
- Fixed scope and price before build starts
- Weekly working demos and human approval gates
- Training, documentation and 30 days of hypercare
- Your code, data and IP, owned by you
See Stack18 pricing or compare fixed price and time and materials.
What we have shipped, and what a typical engagement looks like.
Delivered projects link to the full case study. Illustrative scenarios describe typical engagements and are not named client results.
Lending platform
- Challenge
- Partner integrations broke after back-end releases.
- What we do
- Contract tests from OpenAPI specs, functional and permission tests in CI, blocking breaking changes.
- We would measure
- API test coverage, defects caught before release, breaking changes caught, against a baseline agreed in week one.
5 weeks
Quick commerce startup
- Challenge
- Microservices changes caused checkout failures.
- What we do
- Integration tests for checkout across services, with mocks for payment and delivery partners.
- We would measure
- API test coverage, defects caught before release, breaking changes caught, against a baseline agreed in week one.
4 weeks
Ethnic wear D2C, Jaipur
- Challenge
- A ₹100+ crore brand needed website, app and back office to share one catalogue and one record of stock and orders.
- What we do
- Nine specialists built website, mobile app and ERP on one connected foundation in two-week sprints.
3 months
Read the case study →We agree targets before we start.
Free API test review
Share your API specification. We propose a test suite.
- Coverage plan
- Tool choice
- Effort estimate
API Testing questions.
Cost, timelines, integrations and ownership. If your question is not here, ask a senior specialist on a free 30-minute call.
Ask us anythingHow much does API Testing cost in India?
Most API Testing projects start with a QA Assessment (1–2 weeks, fixed price), which fixes the scope, team and price before you commit. API Test Automation takes 2–6 weeks at a fixed price. Prices exclude GST. Cloud hosting and third-party usage, such as messaging, payment or AI model charges, are paid at cost.
Which tools do you use?
Postman and Newman, REST Assured, Playwright, Karate, Pact for contracts and k6 for performance.
Do we need an OpenAPI specification?
It helps, but we can create one from your existing APIs.
Is API testing better than UI testing?
It is faster and more stable, so most checks should sit at the API level, with fewer end-to-end UI tests on top.
Can you test third-party APIs we depend on?
Yes, with monitoring tests and mocks for test environments.
Do you provide API Testing across India?
Yes. Stack18 is headquartered in Jaipur, Rajasthan, and delivers API Testing for businesses across India, including Delhi NCR, Mumbai, Bengaluru, Pune, Hyderabad and Ahmedabad. Work runs remotely with weekly demos, and on-site workshops are arranged for key milestones.
Let's scope your API Testing project.
Tell us where you are and where you want to be. A senior specialist will reply within one business day with next steps.
- Free 30-minute consultation
- Indicative estimate after the call
- NDA available on request