Application programming interfaces (APIs) have grown right alongside the growth of cloud computing, microservices, and AI integration. But with that comes a less welcome development: more API attacks aimed at stealing data, gaining unauthorized access, and disrupting services.
Cybersecurity company Akamai’s recent State of the Internet survey says, “APIs—long overlooked as a point of vulnerability—have become the primary attack surface” for many organizations. According to the report, API attacks rose by 113% from 2024 to 2025, impacting 87% of organizations surveyed.
Improving API security is just one of the many uses API testing tools can offer. The right tools can help you improve the performance, security, functionality, and effectiveness of your APIs. Here’s what API testing tools do and some of the most useful options for developers.
What is an API?
Application programming interfaces (APIs) are sets of rules that let different software applications communicate with each other, share data, and trigger actions. They’re the glue of our digital world, acting as messengers between the different digital tools we use every day.
In ecommerce, APIs connect platforms like Shopify to essential tools like payment gateways or marketing tools. APIs provide the language that enables these platforms to communicate and take action without manual data entry on your part. APIs are the reason developers can incorporate AI agents to autonomously handle routine tasks like customer service and inventory management.
REST vs. GraphQL
In ecommerce, most API systems use representational state transfer (REST) or GraphQL. REST is the dominant standard, used by more than 90% of organizations. It communicates through HTTP requests.
GraphQL is a newer query language that lets developers request exactly the data they need. All new apps must use GraphQL as their primary API to be approved by the Shopify App Store. Shopify still maintains a legacy REST API for older apps, but developers are strongly encouraged to migrate from REST to GraphQL.
For Shopify app developers, building apps that integrate smoothly with the Shopify ecosystem is essential, and may be required for custom apps to be approved by the Shopify App Store. Review Shopify’s API Documentation for details, resources, and tools for building compatible apps.
What are API testing tools?
API testing tools verify that APIs work as expected, communicate correctly with other apps under varied circumstances, and are secure against outside threats. They support basic, functional API testing and performance testing under complex test scenarios.
In practice, these tools test APIs by letting developers send test requests, inspect responses, and identify issues before the API goes live. Most API software testing platforms specialize in one or more of the following categories:
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Functional testing. Confirms that API requests return the correct data, errors, and status codes.
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Performance testing. Measures speed, response times, and reliability under complex test scenarios such as traffic spikes and high request volumes.
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Integration testing. Verifies that API integrations and webhooks work correctly and effectively with other platforms, including Shopify apps, external services, custom integrations, and systems via. CI/CD pipelines
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Security testing. Evaluates whether an API protects data through authentication, authorization, and other security controls, guarding against potential attacks and breaches.
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Continuous testing. Runs automated tests throughout the API development process to help detect issues and errors early on, and identify problems that arise from changes made to the API.
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Exploratory testing. Uses manual, hands-on testing to help developers discover errors, unexpected behavior, and issues that may not be detected using automated testing and standard test scripts.
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Webhook testing. Verifies that webhook events (notifications that trigger when something happens, like a payment) are sent, received, validated, and processed correctly across connected platforms.
Best API testing tools
With hundreds of API testing tools available, the right choice depends on your needs and existing framework. These six API testing tools cover the main categories: API security testing, functional testing, performance, and webhook management. Each is compatible with Shopify’s architecture and integrations found in the App Store:
Postman
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Best for: Well-rounded API testing and test automation.
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Protocols: GraphQL, REST, SOAP, and gRPC.
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Testing type: Functional and continuous testing.
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License: Commercial.
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Pricing: Free, with paid plans starting at $9/month/user.
Postman is a widely used tool for API testing that excels at continuous testing and functional testing. It has an intuitive interface and a broad ecosystem of plug-ins and integrations, including CI/CD pipelines. Paid plans allow teams to collaborate. However, its performance testing capabilities lag behind competitors. Postman has also leaned into AI, offering Agent Mode for managing multiple task-specific AI agents.
Insomnia
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Best for: Simplicity, speed, and exploratory testing.
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Protocols: GraphQL, REST, SOAP, WebSocket, gRPC, and MCP.
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Testing type: Functional testing.
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License: Open source.
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Pricing: Free, with paid plans starting at $12/month/user.
Kong’s Insomnia is an open-source platform for quick debugging, scripting, and exploratory testing. The platform simplifies API testing, and its minimalist, lightweight interface prioritizes speed. Key strengths include broad protocol support, multiple integration and plug-in options, CI/CD automation, and flexible storage (local, cloud, and Git). It’s better suited for manual testing than automated tests. Insomnia also has an AI-native protocol that enables tool-calling for AI agents.
Bruno
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Best for: Git-native API collaboration.
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Protocols: REST, GraphQL, gRPC, and WebSocket.
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Testing type: Functional testing.
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License: Open source.
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Pricing: Free, with paid plans starting at $6/month/user.
Bruno is an open-source API client that stores API collections directly in the file system rather than the cloud. It’s Git-native and offline-first, with excellent environment management. API files live alongside application code with collaboration handled through Git. For developers who prioritize privacy and local control over cloud-based editing and collaboration, Bruno is one of the better options available.
Hookdeck
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Best for: Webhook testing.
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Protocols: HTTP (Webhooks) and AsyncAPI.
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Testing type: Webhook testing.
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License: Commercial.
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Pricing: Free, with paid plans starting at $39/month.
Hookdeck is a webhook-focused event gateway that lets developers receive, inspect, replay, route, and monitor webhook traffic. For Shopify developers, it’s particularly useful for diagnosing event failures and other webhook issues at a granular level. It is narrower in scope than full API clients that specialize in tasks like REST API testing but useful for webhook-heavy Shopify app workflows.
JMeter
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Best for: Performance testing.
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Protocols: REST, SOAP, HTTP, JDBC, LDAP, and JMS.
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Testing type: Performance testing.
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License: Open source.
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Pricing: Free.
Apache JMeter is a well-established tool for API performance testing. The Java-based platform has a large user base and a broad plug-in library, including CI/CD integrations. JMeter supports customizable test scenarios and multiple protocols, making it well-suited for large-scale simulations. However, its clunky interface has a steep learning curve compared to more modern tools.
StackHawk
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Best for: Security testing.
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Protocols: REST, GraphQL, gRPC, and SOAP.
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Testing type: Security testing.
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License: Commercial.
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Pricing: Free, with paid plans that have custom pricing.
StackHawk is a security testing platform that lets developers run regular security testing before apps go live. Key API security testing features include dynamic application security testing (DAST) with broad protocol support and automated recurring scans. A free version is available, but most features require a paid subscription with custom pricing available through a sales demo.
API testing tools FAQ
What are the four types of API?
The four main types of APIs are open, partner, private, and composite. Open APIs are available to outside developers, partner APIs are authorized for select third-party developers, private APIs are used solely by a single organization or developer, and composite APIs combine multiple APIs into a single request.
What is API testing?
API testing checks whether an API works as expected by sending requests to the API endpoints and assessing its response. Use API testing to identify errors in functionality, performance, load handling, contracts, or security.
What are the three types of testing in API?
The three main types of API testing are:
- Functional testing. Checks whether the API endpoints return the right data, status codes, and error messages.
- Performance testing. Measures response time and reliability during traffic spikes and peak request volumes.
- Security testing. Checks whether the API can protect data, authenticate properly, authorize actions, and resist attacks.
Which API testing tool is the best for beginners?
Postman is an accessible starting point for API testing. It has a user-friendly interface and free tiers that cover both functional and continuous testing.
